a comprehensive review of helicopter noise literature
TRANSCRIPT
Report No. FAA-RD-75-79
A COMPREHENSIVE REVIEWOF
HELICOPTER NOISE LITERATURE
SftwoB. Magliozzi•l Z ~~~~~F.B. Metzger"", o;: x
W. Bausch / ,,
R.J. King
/,italSit- 0.
June 1975 L
Final ReportDocument is available to the public through the
National Technical Information Service,Springfield, Virginia 22151
Preparid for
U.S. DEPARTMENT OF TRANSPORTATIONFEDERAL AVIATION ADMINISTRATION
Systems Research & Development ServiceWashington, D.C. 20590
BEST AVAILABLE COPY
N[SCLAIMEI N O1TICE
THIS DOCUMENT IS BEST
QUALITY AVAILABLE. THE COPY
FURNIdSHED TO DTIC CONTAINED
A SIGNIFICANT NUMBER OF
PAGES WHICH DO NOT
REPRODUCE LEGIBLY.
Ttci..col Rep.., flguceawien. Peg.
FAA-R r5-79\c.... .... ,..e.gi.
"S , .un~d76j A Comprehonsrve Review of , s... c.* Helicopier Noise Literature.,
B. Magliozzi, Fj. .etlgeI. W. BauschI R J /u
- 4 1~~~0 if.4 ~~~A5Hamilton Standard, 0 vWes*of Uifted Teelilge Corp. . 36317
lWindsor Locks, Connecticut 06096 Ot-FA4W--47
U.S. Department of Transportation SURVEYFederal Aviation AdministrationSystems Research and Development Service Id. 1s'_'_ Ini(4Wa.!tunjon,.D.C. 20590 _____________PRfl-W(2fllL-Af7l
This report summarizes the stateof-ttwat in helicopter noise I: inckludesa biliophy ofreorts on all compwnents of helicopter noise including main rotor, tail rotor, engine and gearbzox. Uteatuhre on hellcopm noissreduc.tion arid subjective evaluation of helicopter noise wee also Included. Capsle summaries of Importanrtrepor to amincluded which dlemribe the purpose of the report, summarizes the uimportant results.compures; te epor withothers on the same subject, and provides a critical evaluation of the work prevented. It is conc:65ced the the aval-*able prediction methodology provides a moons for estimating helicopter sources on a grow bernia. Mwowver, themechanisms of noise generation we still not fully undersood, althoughs the experinental end theoretical tools wenow available to conduct the definitive experiments and seetablish the mathematical models needed for ecetreisdefinition of helicopter noise geneation mechandILus Spectrum enalyses of helicopter ranie show that main rotor,tail rotor, and engine soures contribute sipVlflcany to annoyance. In cases where these sources have been heavilysuppressed, gearbox noise will also appear as a significant contri butor to annoyance. Therefore. quieter heicoptersmust include supprousion of ali nf thou compenents. For certification, the literature indicates th at new noise unit-is required. This unit may use the effective nercoeive noise level cocps but should include conrrctions for impul-sive noise, corrwctly address the influence of tones througisout the frequency spectrum. extenid the sp,4trm ofinterest to very low frequencies, &id correctly address the annoyance of noise comnponents below -0 Hiz. Foraassaing the community acetance of helicopter noise, modification of the Day-Nigiit Noise L.WItobWa 5promise.
Helicopter Noise Bibliography This document Is available to the public througit theSubjective Response Rotor Noise National Technical Inforinatiost Service, SpringfieldImpulsive Noise Gas Turbine Engine.loise Virginia 22151.Gearbox Noise Annoyance Criterias
* Noise Certif ication CriteriaIS.S.,..~ C...f.i~iC.,*...s W. se.t.... C1.4.1.. 4#A .4.6 P.") # Pites. [22.P..
Unclassified Unclassified 19
Fer. DOT F 1700.7 57 10.LPRODUCTION OF THIlS FG:.'t IS AUTHORIZEDVertical 1 itiv dentote,; chanpen.
Tumo " . ,.
r-..
44
"(,'II'IT
',: d,.', ~.: . i. dOi en%1 . ti I tdl aim:, r Ith po.ii. ,or-hfi p of
*...." .... .1'4 Tr'aJsp. t-•, t; in ill Ili- intaorest of infer-1. J'.1..a , "|.*. T t 1 iiL-Jd Stit es (Gov).- ic•i ti a ssiu.es rnij
* •i i:. ~r. * t L vCM t Vta 111 urr uise t he-re.cf
Ii a - -a i
I- I
a.' I 1 .11ill! lit pI -
* I I* a - -I -� a 0* a 4
-� I g a I- !:�-
=V
0a -* I*
Ici. j !� � -'* 0� a -,
13 *- a-
- - �* -
-�--- x '- � e
II
aciI-� or or ii co cc cc � ii oc ,c ci u cc 01 II
I I- . F V F �'. . , .* I I jIi�.
Il If* II !:':.
�U
I 3 7
Sdaa.'. 0 --hII�� � U
a. -- -� I..- * -- at.EE�. a--
irs --
* a* � *I�� �! Ua'a
-
a* .�- S � ala... *� �a � *�I � a* �
- - 3 aegoo@ooE �- a'
3*.� ***� *� 'U -�
4
* -I-U a'S a'-
sty'
TABLE OF CONTENTS
Page
-[N R(lC 1'10N ....... ............ ..... . *...........1
SUMA11Y .II ............*......................... ....... ..... 3
HEI-10)PTE:lt NOISE SOUIR.ES **...................................................7
InltrodIuction.......................................................... 7
Rotor Noist ................. 0 ............................. I.. 8Rotational Noise, .................... *...............*.a. aBroadband Noise .... ........................ .0.0.0 13Impulsive Noise .......... ........... ............... ... *. i
Introduction. .... .............. ............ *. .... 18
Jet Noise ............................... 19Combustion Noise ............a................. 19
Strut Noise ... ... ........................ ............ 22
Compressor Noise ..... 22
Engine Noise Suppression *.................. ...... 23Introduction .................................. 23
Reduction of Combustion Noise .................... 23Reduction of Turbine Noise 0 ag 23Reduction of.Strut Noise2Redluctionof Comnpressor Noisee .............. 24
Gearbox Noise .................. f........... 24
HELICOPTER NOISE PREDICTION *...................... 29
HELICOPTER NOISE REDUCTION TECHNIQUES ..................... 31
SUBJECTIVE RESPONSE TOAHELICOPTER NO ISEN.......T...... 35
Introduction ......... 35
Noise Rating Units for. Helicopter Noise Certification .. .... 35Background r t........................................... . 7 35New Rating Scales for.Helicopter Noise Certification 3............ 3
IAII I.E {il- ('( P\ 0ITNI S t('C)Nil'
Page
. l It V l .ut : ul: ...............................tt~tck~ronif . ............. ..................................... 34"
Vim;- t ':.r ('Ciminxunity Acc i-pt.nc, Evaluation ............... 40
S,,;t '.< €, S" . ..................................................... •41
.\IPENI)IX A -APi, .V.: II\IE\S -" .. :I.UTEI') REPORITS ........... 43
.,'r \,,s. {' C.1 11111 lh .L'i , ...................... ......... 43i-oU';- 01V1- ........i.h ...t....i.mt rh. ................ 71,,rN'u-nIrci........................ ....... 109
sRb,.trtiv. l ..- iio C suh. Sumriirivs .. .... ,...... ......... I ..... 121
R{EFU MMI 1*.,sI'. ........................... , ...... 0. ...... A ..I..... ... 1.43
r Nu'....................................... ............. .146
Ilt-Iioptcr .NotIs. Priztil'ticn ............................. 0......... L50
h+lc'.optr N•tst. 1tt-duction Tt+hrifElitts ............................ 151Suhjt'€c'ivt" RI.spon.ls4 to I Iellt.tprtr No.mt ............... .. ... 152
IIELI('PTL' .()ISE BIII.I¢(;IRAPIIY .................................... 155
iv
INTRODUCTION
The helicopter is a complex vehicle from a noise standpoint. Significant noise pro-ducing components in the system include the main rotor(s), tail rotor, engine(s) andgearboxes. Differences in vehicle design philosophy cause differences in noise char-acteristics; e. g., some vehicles use a main rotor for lift with an antitorque tail rotor,other vehicles use fore and aft main rotors while others use meshing main rotors ordual contra-rotating main rotors without a tail rotor. Differences in rotor designphilosophy also cause differer..es in noise characteristics since some manufacturersmay use high tip speed two-bladed main rotors while other manufacturers may use asmany as seven blades operating at lower tip speed.
Research to establish prediction techniques for all of the important helicopter noiseproducing components has been under way for many years. In many areas the acoustictheories relating the generated noise to aerodynamic and design parameters have beenfairly well developed and appear t. t adequate for current needs. However, as thisreport will show, there are many areas where the noise generation mechanisms arejust now beginning to be understood and othern where much further work is required.Also, the aerodynamic inputs required for the noise calculations are often Inadequatefor satisfactory noise estimates. It is thus apparent that the noise prediction method-ology is inadequate due to the lack of tools required to define the unsteady aerodynamics(i. e., fluctuating blade loads) rather than in serious limitations In the acoustic theories.Fortunately, the helicopter as a military vehicle has benefited from noise controlstudies oriented toward reducing detectability. This has resulted in a body of know-ledge which can be evaluated in terms of annoyance when helicopters are used ascivilian transports.
The purpose of this report is to provide a current bibliography of reports describingstudies of components of helicopter noise, provide capsule reviews of the more signif-icant reports, summarize the state-of-the-art based on the literature; and discussareas where further research is needed.
/
1/2
t' i i, l 'l'wLI .' ntatti.i4 -tht.i-1i" n i i h•cli,(-it, r ni.si)' , i., reviewed1. A 'as- i-Valuatci-~* Ic uii. l,,i-. . .ul.ti0isn.s ad ,J! t. ,a". :r,.iti,0a:i, hr,,:Iall,1 a,:, and impulsiv.-. eni r.e, ge:ar-
I. %. . and hlic .'ti .'" sa, pr',n. -Ii,,a antil's.l;,,,ll0v; hulicopter noise reductitun tech-1'1Lq .&; 2 .111d ,llsi,,t- ctM .',., .. -v:Ilu tit in lit h-lic,- ih.. r nijs.. A bilhllography of.,v,.*1- lOa v%.. t I- .. In 1h1.1.1 stljcc'ts is incluhal,, :ilong with capsule summarics of'impor-L.:l1| rt-pi;t-• f1",1131 lh,. Iil, z;p
fi.l(t:l 1101iNI vi)lisli.,t ,.1t it.icro. to, Ir.,luenc't .ani'd hir,,:0.lh:ind components. Thie discretetv.juiu'nc\" t',np,,nt.I. ets . 1'1," f . il tro. i as r't :tijon:al noise harmonics and occur at
::.:.i l )1* 61i .I 1 ath" p,,ass:k'" '-,ut1IwV. n t'' itit.ition.iI n iti.• i4 a result of tL-, rotating
ret''ýI fie'lai t-;a~lsea hv thtc rutur hlalcl, lo:..ling, cije !o thrust. Interaction with in-Ltst-c turbultunh., tip ' 'orties ain.• AH1? : 1 mVtriV inflow van Significantly enhance h-r-iniiifc. vo•'itc'tl of1 ro•tati:nal noi-,-. Cy;-lic pitch and fn-ward flight can give rise to a1Ma,lde hl:oding whit h -ai iv-; onc..e iMr revoluitin. Undler certain conditions this can giveris,, to inipulsiv, nfc.-i:, ch.iract,.riz67A t.o hihgh!v ,,a,.'. iag "bangi•'g bounds. Broad-b;ind randtm rois. in tht r'otor sj •€.trun, fornaerL'r i.k:dl "vortex" noise, is probably• I.a % *.. I ntVraetiti 4s th, Ill:auh.s vith inflow turleul,:nre..
In talculatijns of rotor harmonic noise, the steady loadhi.g methods are inadequate toe.xplain the high l ow..f mev..iurd harmonics. Unsteady loading of the blades isrceiuired to imiprove ifhe correlation .tlwetin calcuLations and measurements at highharn:-nic ord,-,s. In open-form :rolution,, instantaneous blade loads are computed atmany angl•ar positioms and several.radial stations (luring the rotation of the blades.These loads art- then nuneriuallv integrated to define the noise at a given f[eld point.rhis approach is generallv co ' tly as It requires long computation time. The computa-
tion time can ie significartly reduced by assuming an analytic form for the azimuthal-variation of bl•de loads (flos.d-form solution) ratherthan the many descrete poin:sr.-juir,.d for the open-f rm solution. The integration can then be done analytically.With tt.w exceptiioni, such -is for impulsive noise, closed-form solutions give compa-rable results to opin-forn solutions. Results using this methodology are greatlyimprove-ld oetr the stvady lfading formulations. However, some deficiency In highfrel'ue'ncv noise prediction remains. This has been improved by hmodifying the un-.Mttadv airload inputs to account for uwfttady vortex effects as measured in wind tunneltests.
It appears that the existing nFloi.;e Lheorie5 ar'• adequate for good prediction of heli-copter rtational hois:. '11e limitations in the methodology appear to Heh in the tefiai-tion of the fluctuating aerodynamic blade loading inputs to the acoustic theory. *Sincethe fluctuating blade loads cannot be well predicted analytically, empirical (or at leastpartly empirical) methods for estimating blade loads are required for predicting therotational noise of helicopter rotors.
Trhe origin of rotor broadband noise is probably the turbulence in the flow seen by therotor blades. Trhe prediction of rotor broadband noise based on rotor geometry amdoperating conditions using empirical procedures has proved acceptable. 'The successof such methods is misleading in that they do not model the detailed acoustic processes,but rely on generalization of existing test data. The recent impetus to study broadbandnoise is the result of reducing helicopter data with improved equipment that shows thehigher f requency components of the spectrum to consist of peaks at blade passageharmonics superimposed on a lower level of broadband noise.
Impulsive noise is generally considered to be a special case of rotational noise. Twobasic mechanisms are believed to he responsible for impulsive noise. Interactionsbetween tip vortex filaments and the rotor blades are one major cause. Compressibleaerodynamic effects are the other major cause. The major limitation in calculationsof vortex filament interaction noise is the difficulty of specifying the details of the in-teraction of the filament with the blade. This is due to the complex trajectories of thevortex filaments and the blades. The impulsive noise that occurs during high speedcruise of a single rotor helicopter Is believed to be caused by the compressible dragrise on the advancing rotor blade due to the high resultant of rotational and flight speed.As in other rotor noise prediction areas, the specification of the aerodynamic imputs
for the calculations require further work.
Engine noise research has received recent attention because of its importance inIturbofan engines. The noise components of engines identified in these studies are jetnoise, combustion noise, turbine noise, and compressor noise. Jet noise In helicop-ters is not considered significant for current helicopters because of the low exhaustvelocities of helicopter engines. However, it may become a significant component Infuture quiet helicopters. Combustion noise, which appears as a broadband noisewhich peaks near 400 Hz, is the dominant component of engine noise. Turbine noiseappears at higher frequencies and consists of tones, pseudo tones, and broadbandnoise. Compressor -noise occurs at high fr'equencies an 'd Is the lowest level componentof engine noise. Compressor noise is easily suppressed with sound absorbent ductliners.
Two approaches to engine exhaust noise suppression can be used. The first approachreduces source noise by changes in design or operating parameters. This appearspromising for futare engine designs, but results In increased weight and size or In-creased fuel consumption In present engine designs. The second approach is the useof acoustically treated ducts to attenuate generated noise. This approach invariablyadversely affects engine performance and also results in Increased weight.
Gearbox noise is not generally a problem in current helicopters. However, quieterversions In the future will require gearbox noise suppression. Significant progresshas been made in understanding gearbox noise mechanisms over the past eight years.This has included development of both analytical and empirical noise prediction
I
MI
r *;IU~t I hv !~- I;' 141inpii l ni-hofk.i are ro. hatr w -l tsyi to use. anfd ilj,,)ea r to otterlw, n.%-! mi arxac. In hv'ilk ulpl.r ippulit-ations4. A1%Ia nkcth-Wis,.on tht. other
;11 * * 1, a . I' Pit %I1 .. 1 )1 11a t.4~ 1,41 .ied : .t, j:d .1;ni;'t inn lit u~t*e anti 'it 11 re±'-uire some--..z .1 LI ri%.'-ta ive lo br .-.tsoni.,lilt agrt'vii.elit wth txpi-rmrent. It appears thait the
p! ... : 11 pIII vdU rt.",: Jlit. 11C .O' to 4-t~t Zhtt- ltv- k (if .exi.sing izearl'-oxes, % bile
I ~. ~r" ~'i~ulpr. cate lurt, art- moilrv u:~d.; ful ainia.snosine flr hiui~:: prolalemsi e gear-
;rt'.-tion2f 4~ not.-.'' for rmi. et-t he.'Iiýaopt'rs h:,,. rec-entlv received sai- at~entiofl.sIN * I 1v'4-fit ' I.) i ro(*-irs' h 1.')W av:d I~al.Ie. iajqw-'r to be *adcquale for sItudies of
- a..::::i~ .. a".t~au '. ii'- ji~ieiIri~.arv t'ehiv!c oricuend and do not appear
* A 1*.`. i.-W 4d tA\1 I,vrl4flE'nt: prograufls Ic reduce. thic flokL* of existing helicopte~rs showedthaL i'oW**1- ntwj:-I- el van lit- :atitha.'ve, hut at thei etzjwflni of f-fre lmnce reductions
.!nSi wi'a,.ist Ro s'-' ~ tor noj*es rtaluction was atwainvd b * reduzzing itip speed, ia-crt:t -.in*, rutur ~t livt A adtdini, bladcH, anti by limaited blade aerodynamic improve- -
w.ihjl*' v i-t *'-:.~rdutedt pz'aniarliv liv Irst~a~lationk of inlet and exhaustn,,ui~tqr:;. Gusarls,iix ia:,.wa was reduced( priniarily by installation of en-c'1'Jsures aroundir.ht *c.tarh'Ax an([ It. :appli'ation of thirmping mAf ri~aI to *gears and shafting. These noiseIc-*!,;' tiflinfsInuu. w..re effsd-ivt' but unight -lut Iii acc'eptable fir comimercial trans-
* W'rt" h.'Iicutii'-r I,.i'-ust of th'-ir wsji'ht and pe r."or mance penalties. Fu rther researc~ha -, ri'juirt.-d in tht' ,iwis rediuction larva to daofint- rotor- and engine configuratioins. that;s r* both quie't and cffivi' 'flt.
Sulbot i.(tvs: I'espoflsi to aireraft flaisL* must hi' considered from two standpoints: air-!1i:iff nofise' ct'rtirii'ation and c'cainvnitv rewc'tion. Inthec firpt area. P. s~cale li neededto ritva:urt' the- p.-rvis'd 1.'vel (f :an incliviidt'id aircraft flyover soitnd-- In the second:ir,., a~ roi'llfuflit.'. .ac'cptaine.e c'afrulation jp'oe'!sure 1i6vhlch a.'curately evaltuat,?s the1-.ra; te'rra effeets %in aircraft ricist- on cominhfuzities airound airports i's. required. Fornoi -z ct'rtifi-ation, setrirats U'-fic'iercles ex.iAt in the existing ratL'ig scales because ofth~e siginiific-ant Uiffr1 tln(flC(* b'LWi ..- he'li(optvr noise and noise from otL~er'type_1v M ~r-c i :aft. Mlss'd on ihe data f ro-ni the' literaturv, it appears that the helicopter noisevertifica~tiosw unit will ust' Effec'tivP Perc'eivec:N!'~ Level as the- basis for develop-mvt Reivisio'is apptlar not4ayto: 1) -,-os~e the payechoacoustic response (Noy)vu.-vvs and. ex'te'nd thvr.n below 50 H~z, 2) us. irattgrawdc duration correction as use-1mn FAR( Part %;' %i:thi-r than 10 !ogji 0t/174 1%;;nrc t is the time, in wsetonds, between,10) dBJ down pointsi, 3y irectud(' the effects of impulsive notse, and 4) :-orrectly a~ccountfL'i' th-Ve s.fi!w. Of (i:eVrtet frequency nioise be!A)w 500 Ik~. rhe data from the literature';uppcmrt t.he use of some v'u'rs-ior. of the Lcln voahcept for community aeccotance evalua-tion. The basIc unit for L~i calculation might be (111A c-irrcctccI fo.- pure tones andtIhiration as described above. impulse noisc pe.tli wotaid also be included.
5/i;
HELICOPTER NOISE SOURCES
Introduction
['he principal helicopter noise sources are those associated with the main rotors ormain and tail rotors, drive engine(s), and gearbox(es). All these sources give riseto a broadband noise spectrum extending over the entire audible spectrum and to dis-crete fiequency noise, which may or may not be detectable to the human ear. Undercertain conditions, helicopter rotors may generate impulsive noise, aescriptivelytermed "blade slap" or "banging".
Rotors produce noise due to the rotating forces on the blades and the displacement of
the air due to the blade section area. Also, at high tip speeds and/or high flightspeed, the flow over the blade section may exceed snaic velocity and a local (and thusmoving) shock is generated. Finally, fluctuating blade loads may occur due to inter-action with atmospheric turbulence, tip vo.'tices. or the flow from another rotor.
Engines produce noise over a broad frequency range The engine inlet compressorgenerally contributes to high frequencies and the engine exhaust dominate- at lowfrequencies, although turbine tones may occur at high frequency.
Gearbox noise can be apparent in the noise -lguature of a helicopter due to directradiation from the gear casing or from reradiation of the structure coupled to thegearbox.
Extensive literature exists on the understanding, description, and prediction of thesesources. Studies range from simple empirical equations showing the relation of afew gross design and operating parameters to the resulting noise to extensive openform solutions requiring detailed design information which can be applied only bymeans of a high speed computer. The state-of-the-art in source noise uderstandingand prediction has by no means progressed to the point where all aspects of the pro-blems have becn fully developed. However, .he fundamental noise problems arereasonably well understood and predictable in principle. Application of these theoriesto the design or redc sign of helicopter components has generally resulted In noise re-duction, although a deeper understanding In many areas, especially those related tobroadband noise, is required for substantial reductions without undue performanceand/or weight penalties.
The following discussion presents a review of the literature on the historical develop-ment of aoise prediction methodology, summarizes thp current understanding of basicmechanisms, and presents philosophy aid results for the reduction of heheopter noise.
7
! t I:f. (-)-' .~tainfs th~irreti frcltiuinow u1111i41)iltit.i awl thro:cliand vimiponents. Theis Clinponei uts a rt. rtis irrcd to wz notationrial nui..ie ha rn'..~nici and occur
.~:~~t j.~. Of OW W-101- lXU:4A~ge-f.iuuc l'lait: ire cvauýými- by tYhe rotatipg pres-.,ur~ I :t.i. i atistal I-v fl-.. roltor hL~aiti ioasdi.1-. -lu' to~ thL-t thru~.-t. Also, in cases wherear r~a~ .r tn uth ir-ig.9ted turltiu'ncs! Or !mtwvi n rotorm, isr with thIi, tip vcrtices occurs,
:I r'JMAZi~a Iluý-tuatjn.g Ipri 4urL fiClO rivSUlLS which k-'ar sii-t a tl inrea*se the har-Is..!i v v *n. 1!nt .,f r.)t:tti.n.Il nois'.. Cvclir pitch and forwacd flight (can glyti rise to a1jl.,s!- !..ai.1juz which v~aries omit' pc. r revcIt itai-. I :Iniot ve rtain conditi~ns le. g , if
it,'U .rwrl tnittc &,1v s such thaft the til) M'hnuin~lwr of tl.t ;auvanclong bla:de exceedsm,oMt I. ritival %.aluo.i, flus van give r irte to lanjaulshiver..* characte.rized by higbgly
:Ln:g. i. 'l):Ingir.g* so)undsl. T'he iflwi)Oi..ve no.lse is cha~ractLerize'd by sharp' pe~aks in-he:ia-u.- pr -sur, time :Rsv.lan-Itina. noke~ fi riam'ri-lv as called I.rortex'
rnolse, but in-.-k-.t.ig.it4ors now peeft-r *1aodih noibe, :-ircce vortex shedding itselfis not Illtevoed to be the principal nit*chanisir.
R-.:atjsinld Noisa* - 1; .)r to, !he iidr, (il t n. :thtAd was used exti-inelvely for pre-dictin..t tht''oii fro'rn p-.pollers. fans, aiial rotcz-s. In this. th..-oryv, a distr~butlio4 of-;our,-,-- whit L are fixv.i izL sp~ave are' *trirgvre.'u by *thMI passing~ bl:idL's. The. strengthofi the %our, es is d.-:teinminedl tL tht rotor abr-u-t an.: toýrtue assumed V.) act at ancff" tive radiu.-, t% piwally at 0). .1 time.is the actual radliu:.;. rhis analysis is valid fora st-itic. propeller and :at distance' several diameters aw~ay (far-field noise). Hubbardand Ite-g ier . ri-fineJ Oniir's fundramental equation..; without some of the simplifying.ais.'ulfpti.2nr of the firivirial paper. This ri-moved Gutin's restriction for fLr-fi1eldnoise and aillowed c'alcul~ations of noise in the' near-field to distan~es within one bladechord. of the tip. Also, the actual radial blade load distribution could be utilized.G;arrick an~d Watkin's: e.xtentied GutixV % theory to th: case of a propeller with forward,sixee.d for an observe'r moving with the san..- vcoc~ty as the scr--e (ILe., a wind tunneltest). The results could also be applied to the case of a stationary observer. providingthat the i-orrect iOistantana'ous distances wi'ri; useud und the f-requencles corrected forflsspph'r s~hift. Finally, Watkins andt lur!ingl (orn'Anfed these effects and Includedeffectsz of a rhordwise blade loa~iing. Horwever, the.se methods, which a'll assume thatthe Madire loading is constanit with time, were found to severely c-nderpredict the level.of the haxrmonics beyond the second or third.
[hei realization that unsteady Mlade loading (i. e. ,a blade loading diatribution whichVarie-d with tirniii could co'rtribute sij.'nific.inlt v Ito the noise generated by a rotorprompted an extm'n.-ion of 1(tuLin's approach and the development of new formulationsfor 61- noise prodluced byv moving sourca's-:- and unsteady blade loading effects6- 10 .
T[he approach of Lo'.-wv ind Sutton1 0 is a similar approach to that taken by Garrickannd Wnt~kins 3 , but extendled to tol~ude in-plane comnponer.ts of forward speed andazimuthal asymmetry. In this aprahteoudpese is computed at any Hield
pproah th soud prssur
poin, by a numc rical integration which utilizes, among other inputs, the lift per unit
span as a fu.cti•,n c. radius and azirmuth. In this manner any radial loading functionand any peri.;" v"aveform of the blade loading at a given radial station can be Inputby jtidicious ... c•etion of radial and azimuthal steps of integration. This approach,while havinr, tAZ'ejl'', can become expensive due to the large number of calculationsrequired in, 1ýe nunmerical integratior., particular!y when using small steps, as isrequired for calculation of the, higher rotational noise harmonics.
Schlegel, et .116 used a similar approach. They used the blade loading harmonicswhich were measured on an .rtual helicopter rotor as inputs to a modified form ofGutin's theory. They conclude that the agreement between measured and predictednoise, as reproduced in Figure 1, is good at low frequency, but poor at high frequency,probably because of inadequate definition of high frequency harmonic airloads.
so
70S46 >' MEASURED DATA
0 ZCALCULATED (UNSTEADYBLADE LOADING)
X 40"30 •-GUTIN (STEADY BLADE LOADING)
-J 20
10 "S
_0 -. 2 3 4 -
ROTATIONAL NOISE HARMONIC .
FIGURE 1. COMPARISON OF MEA3URED AND CALCULATED LEVELSWITH AND WITHOUT UNSTEADY BLADE LOADING FOR AHOVER CONDITION
In both of these approaches, the harmonic blade loading must be input for the calcu-
lation. Such open-form calculations havetwo important limitations. First, the re-quired airloads are extremely diffic..t to predict; and second, the computations are
extensive and often expensive to perform due to the digital computer time required.
Lowson and Ollerhead 7 overcame these difficulties by developing a simplified
rotational noise analysis which uses generalized !oading data instead of the detailed
amplitude and phase information required by previous anviyses. This simplified
closed form method was shown to perform at least rs well as the rather cumbersome,
open-form solutions in many cases, as indicated in Figure 2.
9
A .1, 0- 1*.-a di~n~xJ:t ~d,, t!(( eupt that rertjtir asturrpti;ýas
~*II q~i rjY iz~:tL~nWr1!4'~t~ fori'rul.,tion redu t.ci to an aral',-tical tfxp.resirano~* wt requirti ilumtiriv..1 iuitegr~1ion. Ili-; WgklfiC~ant ConClubiurzl are that the
1,!n.ru noist, in thi, dornznarit raitur n..i.%e* fta'L-h~tfinis anti vortex noise is a n,.gtl-U yi~Ic .'j e' ,tJ~ I~t~ at nori111ii optvratinAP vw itij.,nsl. Al.:io, the haurmonic- fall-43ff wiltl
* *~ t~ 1. if I.isk-alh 1)) the IA.M.dt !wideing -q.;vtra, Lig~rt will be. noise radiatio.n.ablsi Me rg* . 'If, re otatLion (i'x E-on? r~ast With .tL:avav loacding radiation results which would
'A...~. on' aiv~-, und i the tip Iftuc t is idepf-ndtnt ofthe rumber of aL~d#s,:.o* i* rrmw.ving the hirg.~e powtri l~aw ale*p4*flee'rr' n tMadv nuinlwr iad ic ak'd ( by
0 I !1 AtS.ourn oATA
10 0 GUT,?. (5?. AOV LOACDING)
0 SC141C GL (OP~t. F.IRM)41, 13
I a aWSW. & Ott1lI4AD
U)
.,C,-frIt uhoije
I0 I7 4
HARMONIC NUMBER -
FIGURE 2. COMPARISON OF STEADY LOADING, OPEN FORM, AND CLOSEDFORM THEOR;ES WIT-H MEASUREMENTS FOR A HOVER CASE
Tihvr.' are. mituatiun:i ff), which -lomehd-fortr methods are not well s4uited. B.a.alcaliyp0.4. zet he tk a re i n~ale.Ilae gti wh.vit tari:t' :iizouu rh~angtns foceur over a smdlI portion of
Ilh, r'o1or di .r. This; Ialinfgr hch~avior protduves hig~hly directionatl harmonic nofac andi- 1-1na. aaaon V oki,:w a*dI:.1: 1 zpulkve. aoine (.)r sbla,1:!a ship"') on mtost tarndt~rrl rutor hell-r1)ptiers andin xvfl n;in;gie rotor II()tz.Sill(.. tI~ ti, lusvcf-forar. olutiuns i.-mnuine that11w- ;,a rloarI I1 :arinbonvi -irc rainxuoily phamsd :and dxixt their axmplitudesn decrease expo-nionlitlly with h~armaenit' pr'!r, the nolise hi. predicted to I~e constantE azimuthaslly duringhover and syrnm(etricat azimruthally during forward flight. Irapubsive noise Is discussedin I later sectiun of this report.
Much recent acoustic research work has returned to experimental rather than analyt-ical studies. letferences 11 through 1-4 are examples of noise measurement studiesintended for verification of existing noise prediction analyses as well as for studiesof noise generating mechanisms. Reference 11 essentially verified and slightly re-fined Lowson and ()llerhead's simplifying aissumptions. Reference 12 demonstratedthe accuracy of Wright's theoretical approach using measured airload amplitude andphase data, whereas Reference 1:' is oriented towards establishing a base for develop-ing empirical formulae for rotational noise at a future date. Reference 14 demon-strates good correlation on-axis with Reference 7 and provides a preliminary aero-acoustic transfer function for rotational noise. If generalized aerodynamic inflowdata are ever developed, the transfer function approach could become a useful newprediction tool.
Existing prediction methods for rnon-impulsi.-. r,utational noise predict some decay ofharmonic level with inc-easing order. This behak'ior is predicted by open-form,numerical integration of dit:tributed loads methods as well as by the simplified, poiatload methods. flowever, improvements in data an-tlysls have shown that blade passingharmonics may extend into the mid-frequency ranpt, as shown in Figure 3 (fromReference 7), and that levels frequently increase with harmonic order after an initialdecrease for the first few harmonics. Consequently, agreement between predictedand measured harmonic levels deteriorates with increasing frequency.
IJJ
.. .. ... . ... . . .. .. . . . ... ... . .
o ...... .... ... ..i 7 i ; . ....... .0 . ..i ..................... ....... ..................W `-TI.....i..'
... ..
.J
.. .
A. 9 It 4'= Us - ,r 4B• • ,t
FREQUENCY- HZ
FIGURE 3. TWO-HZ BANDWIDTH ANALYSIS OF UH-IB NOISE SPECTRUM
Some preliminary studies by Sikorsky Aircraft15 have shown significant correlationimprovement by adding vortex-induced unsteady airloads to the airloads defined byLowson's "loading law" decay approximation. The unsteady vortex effects are basedon wind tunnel data measured with hot wire anemometers. Figure 4 illustrates thatthe unsteady vortex effects enable a closed-form analysis to predict tLh basic noise
11
S:: : ... .I'..~ I ,,', ,,'., .)11,,, 0 t', IWl,. W t , W,. I , infd I('- Ll, .is . It is lieu.I .d tO --u t
. .' . h. I |to?' U1.I :i'!'. "j gh'.x ,hvvts coul•d Ibe ih..v.Ioped with. .: t i i t t ...: 1., :,tII lullS ;il' ItII) v,' di.,'uratiubns, tcoupled with noi.se
" TI uz.::z: it .,lj,,. : : I,,.'m :W xr,.'. t i ol itht" h rat.tr. 0,, t th,. te isting noisc 'meIthod-. • :'.-,r r.t..t 0:n iv., i!% ,d.,qu:it.l: !r qijc p)( r edi ction of helicopter rotor. .*.', 0. ! :5-a.., , :,)i :1ir t tos i h. III :th e i,.thn' im r bM lad Ioading inputs
: .I v i ; ,I I, 1 ,t w -.t ,,-h•o,'k. A.s Shi.- , #-I AI;, 1onchudel from their-, 0 3. I;.1 III J,'I - " VVII hllt ;zAi~ii and ins:sUl t'vlstent; was. oIt-uintd at low
,... "h ,11c, ;Ilaput ,da:t we're :adeLquat", hut poor agreement was,': .. .. . * ,t . .' . :',',i,:'.c; h:, .1," lacIk- & :i w i.xlyvamic .at:. The .its.,tio.' Is further
-, .. , . i; pr 1.... , :, .... i I .,+ fi.i I h eld around a rotor during all
J% ... A. ".P i,.',,!,!, * . 111 sls, js:rtLIt ul:,r v I;: t : tort.. ca;t" f t.an:h_:: rotors which I.ttr-s;'t .!.. It. If , 1' it Li] l oAtir.s which aIre iih thu nain rotor doIu,3l tiwash.
-CALCULATED WITH UNSTEADY VORTEX
"~ •.- --- CALCULATED WITHOUT UNSTEADY VORTEX0 MEASURED
<. 70 000 C 0+ 00..
_ 3 0 0 00 0O0= oOOoo
0 -000
-; \h 30
1,10 1* 1• 0 20
IIARMONIC ORDER
FIGURE 4. CALCUI.ATED ZFFE'3T OF VORTEX INDUCED
UNSTEADY AIRLOADS
1"
F-
JBroadN.and Noise -opinions regarding the origins and behavior of broadband noisevar ' sjmnewh:it among investigators, but there is general agreement that turbulencein the flow seen by rotor blades is the basic phkysical mechanism responsible forbroadbaind noise. Turbulence in the boundary layer also causes noise, but at a negli-giblV small amplitude compared to blade interaction with incoming turbulence. Thefrequency distribution of the broadband noise is determined by the, velocity of the bladeand by th sescloftetrune 1 4 . Principal areas of uncertainty concern the
efft'ets of velocity on the intensity and frequency distribution of broadband noise. Re-cent experimental work by Leverton and Pollard 1 6 fails to show the accepted Strouhalfrequency scaling with velocity for full scale rotors. Ffowcs-Williams and Hawkings17
make a convincing, case for broadband noise varying with velocity as V8 at tip Machnumbers above 0. 5, instead of the V6 dependence in common use as reported byWidnalllh'.
Much of the recent impetus to study broadband noise comes from improved d ata ;.ro-cessing techniques and equipment. Narrow band analyses of rotor noise have showndiscrete frequency components extending well beyond 150 Hz, which historically wasbelieved to be the transit'on region between rotation.* I noise and broadband noise fortypical helicopter rotors. This means that significant rotational noise contributionsare included in the observed noise behavior and in the broadband noise predictionmethods that have been developed from experimental observations such as the wellknown Widnallib correlation of Figure 5. Work by Lowson~et a114 , and by Leverton
40 TI)Wfq 'r',ý !ft/sec) ELtICOPYERS -SC0 ' t4 Huhti"rd and 269I43
V $91 0300 U: :alT 650 U 450 um.) TR-62-73
35 * F68 60') TCA(C - _ __ - -
* 613 A ?OD-~ *692 9 8C
* 805 91CCStuckey ar1, Goddart
3C
D.1
FIGURE 5. WHIRL TOWER AND HELICOPTER VORTEX NOISE.
13
I I.1 I- I!%!.~ I hat It.1 IjW I I-tLIUent-~v biroadbajnd tw.ise v'juit I Le dlWe ret~n in
I t. :arn.orv., the- ip.:I Iiint :i.2 IVI-IflItII .111 j31. i1 L. tAe( hroai(dIand It i?1i and i~pectrum,
it.ivn -i-Ai -;n 'ito l*n t trx iii u;p'raing 't,. ond itiwzs isi misikeudiIM. Th.±se pre-t :~ I~ ! : v' a~'a ,a~~aI*I' ~~t:~.te:~ ~t t:iav,- 1):,nif or pos.sibly 1/31 octave
1 .- is~ for~ Vt I' :, -.1 1*. to I,,, but h, -wt int-thuds alo not ra':i II- trot Iv the detaileda. I'L. pr .'v- tl it von! uIbuta to Ola total i j~iaI . Conwq"uentlv, it is hot pre-
.4:~tipri'a. auil. a Iai-.tjl,.o nai ro-w I~andI e:tiniAe of rotor noise based on.;L.-': ~iitti1t ~trI( *,i afrr -(I n1.azx1iu preap. qrtiev of ;I ri*lti ;;..stem. Extensive experi-.1 HI :;aI' tzaIwork. it ill flt vds to bc 'lont' to isolate!L the specific mechAnIsms
* ~i~~ Ijo~iI':1i IroAua' niis~.t' aez.. to rteuIj.vti set-ul i v h ii on models.
I I..p '' ir.~i.svu:- -pan1 infi'j:tt.'s thait 'h't:ailtd pretictirion nm'.thods are not available1.uw'ýof, v*t il1. I, tuiwff un(cour-ifi:&g eurredmtiot.9 using measured inflow
:.I~t..,n,.t inl avus eq iiu~atjions. ft predict~ broadbandn fan~ noist' at low speeds, butto;; I,;i n%)t :I v.,-tho~t suittable for ht-Iiioptiri !JrLedi( lions. M'Jthrd,!ý in genera!, haveI'vlit-d imon '*t;'v ia hnroI i'ie da~ta from full 41, ale rooors to ektvelop empirical methods.In thta::e such :as the* 'Sh-lilgul" iquations for broadband noise6 gross geometryIndt .pcralinig condition ifil.ailt ch-ird, bl~ade x!eu, tip) speeud. and rotor thrust) are tVa
* :'a.,ic pair:irter'vr-. *hVh form of these eqjuations wasi rnJified somewhat by MunchJL9
r*, .ul~tain the:fo.. f'ritIAlow.
1') ~ LO [13 Ic* lt A ( IAG J-) I", (CO5 2 0 00.1) 'Sje19. 4 (1
f., I- ii .vt - 211) l.(X; (T) (2)
:~ ri-an~ezIi'~tis vasa'.r to use ý.inet it wwi,i thc basic pa'rameters of Uip speed,Vthr I, aiistanev, r', blade arva, 11, blaile r~diiUS, It, blade %thord, c, elevation"1F4', 1.aril ýpvtrufii .;haipe' (orri'r-(itinf, Sj. Values -if Sj for thie j th frequency bandI hy Munach arv shown in Vigrure! 6i. The' Iit n, fg. Ns the. center frequency in Itz~
I-, a v. %kth Pi-,rure' 1). This flit~thlol p~rovides i~stima~tes of oc tave band levels In fairly.,0'u.i :agnreH'nuant with aacvtwo. hbani tvi'.t data,. but -,univ rotation~al it Is crintributions -ireinvitili'4I in !!)is br',:idI,:iiul nois.e" as dsuw- previou!:ly.
.J-J /S-0
Li 10
0W
J -20W
z /.30 I.
.. L LJ. '
32 16 6 4 a I 2 4 8 16 32 64 128
BAND CENTER FREQUENCY RE PEAK FREQUENCY, FS
FIGURE 6. ROTOR BROADBAND NOISE SPECTRUM SHAPE
Empirical broadband noise rilethods tend to be most accurate for a moderate thrustcondition which typically is near the design point for a given rotor. Predicted over-all broadband levels normally fall within i 3 dB of measured levels. Accuracy de-creases rapidly, however, at low thrust and at high thrust. Problems are compoundedby blade twist, which leads to recirculation through stationary rotors (i. e., when theblade wakes are reingested by the rotor) with attendant noise increases during opera-tion at low blade pitch. At high thrust, blade stall and complex unsteady aerodynamicevents in the tip region of the blades contribute to rapid Increases in noise. Figure5 illustrates the noise behavior discussed above.
Impulsive Noise - Impulsive rotor noise generally is considered to be a form ofrotational noise. Narrow band analysis reveals many harmonics of noise that decayslowly with harmonic order, while oscillograms of the acoustic pressure characterizethe noise as an Impulse that occurs at the blade passage frequency of the rotor. Hell-copters with tandem, overlapping rotors are prone to generate impulsive noise, buthelicopters with 3ingle lifting rotors also can generate it.
Two basic mechanisms are believed to be responsible for Impulsive rotor noise. In-
teractions between tip vortex filaments and rotor blades are one major cause. Com-
15
* ~~. . . . ...~l. hia 1. S't.-s -1, vI :111 dematron~.tr:,te with1 their
* .-a:'.1.n :orlI. i..,raaiwo an 'in ala i f :1 hoverinig. rotor. Of tlhd two
h ~. -. ~ ~~ I~n an t~yaai~s h~a h~~ a a ~*n~ m.~:It(.(]h irnnortant rolte that
'**%~n*****vvor *.nviiii IiAI."*~~.- ina zipul~si~ e n ;I gane r:ation. :Anilvtical nwodels of11 . :~ * c. ai~ mv' ~'~nilsal ipaI Ul~ifri-rives 21,. 22, 2 1j whic1,a IIpIaI
prv~**4:i' 'Ing, s~r~i Ij.. .Igri~t. 'jtudi lavi.1it& wIith measiured. %tt .ie~a~fl.ni
- a ... *ýJ rl *,.wj.. agrt-non fo I n, -tia.I~itA rotor cix-rutin,." in
1'. in;. 1 ' .111~. Iii :~ast ;sr l14Ie liteS it) I'iti :at ing (tho magnitude nf the uncounter
t. *n- v nt tiLia iv'flt. Iii 'artex fiair-on~nts fS rut h ry(ifplex trajL~c:ori2s.
. itha:~~ -.h 'i:4 1' .1 vn I- CJ it -ti tIn I MA-iiviit ion4 Itll ut sti Lnladv ;aidl vorte*x verv dfi-.*U1 it ,,)~a Ill .1-.1Ion lti ssi, n 1ist rib-a ion 1 a1 vtaa mtx uu rt velueity andl the rleeav ofOw.i U bit' u 1 tiifleit. isdjffivul it. as~t-,v- expt-rimeitntaulv as wull as :analvticall V. AiLrthtlr roweifpliu:Ltiin :to if.,- :a'istiv prteditction probIlemI is the sptrating point of the
.4 ill az.! it-:z :eer-a'!% ai.anaic rev.Ibon:-.e -hi r~aetuiistivs. a s pointed *eut in R;ferenve 11.
I I~~~ i n- lsit- I ron'. tanfl'!in roluar hehelispter, involve.s. main'1 fat tars. TypicallY, a
~'pn,~ ;h.d thn o ~ hn ehi-(.iLle Abjow some dc-grev of overlapping of the rotor discs.
Thilnsa. 4e~trLdJ .nust s milpulkive nlaaske from iwt, inr-thanisms. The. inaor one JLi blade-A urzt'x ini-rarntiun, '.Oiarv tht* tip vortives from uric r'.tor pags through the other rotor.TUhe intier:&cttuai te.af oc-cur onl aithur the forward rotor or the aft rotor, depending on.- e-iativs, LI aaIani .I ifti rsiirsa zawal oil tht* flight coundition. The scrond eause of impulsiverwoi -. ira candcicm roto: - with ovi-rlap is valiesd rotor/'Iownwaish interaction, The down--wash tof omne~ rotor p:i~.;*#s tha ough the aothwr rotor in the overlap region. causing apuls:itivc ne -p -aalo uh~aang# iii loading oin the rctor blades. This loadinggi Ve rise it) &mpulsive floisu. B~oting Vertol Company has conducted numerous studies(if noke generation :and noise~ reiluctIon for tandem helicopters that established the im-ptrurtwe( of rotor/'vo)riex inte raet ion and rotor/downwash interaction. Substantive datagi-ner~altv are proprie~tary it) th~e Vertul ConipanY, but soman.q~aantitative -trends aip pre-.-wiltedl in Ittclerunve 21-P whic-h doc-unients aI study of vivil helicopter noise. this studyvonc-luiles that (he only wav to elimninatf- impulsive nolse .1rom rotor-rotor interferenceis~ t-) elininate tavfrl~ap andl to control the vtnrtival separation 'of the two rotors. Figuire7 ks t~alkasn from~ Ranfisrtnen 21 to illustrate haiw separating the rotors Influences noise.
a hte :Ajilitv to pditnoike from tanahnim rotor helicopters with overlap Is not. we 1l(~~~lI :t.a in * pan Iiii r:,turv, alt hough praapriet a ry imethodiology may exist in some
viinilri~nhis. II principle, if data :ar(n avaihlable fro~m te.4t or annilysis to relate vortexI nI r~it lah rt-ligth and ilt)wflwasl vI eiLt to a 4*oifigrur ation, analytical miodels ejxist
to #,'5tijfadt( than noise vavi'f',rin eauwscd by ptilsative changres in airloading on the rotorslarlesi(.
fimrpulsive nokva th~at occurs during, high speed cru ,Ise of single rotor helicopters islielieved to Ihv vauseil by c.ompressible drag rise on the advancing rotor blades. Therotor noise of ;I largen single rotor helicopter (Sikorsiky S-6;5) was studied in Reference #23
I;
si
S .... ....... .4 . .l 4. . .
;i- ,• : 722., ,1 ft/ser- bANe..
- ~REA VY @7'- :A" %. I ROTOR
-N0 SE4
j.I 006"
I .• IiI •
P,
- BLADE -O.2 .0 " 2.0 3.0 BLADEBFLOL FCWARD VWIFTl'X AFT BJ .LE VERTICAL SEPERATION A8CVL- VORTEX FT./.lAJDE CHOD VORTEX
FIGURE 7. EFFECT OF BLADE-VORTEX SEPARATION ONIMPULSIVE ROTOR NOISE
during a program of simultaneous noise and rotor load measurements. Results showthat during high speed cruise, unsteady airloads alone are not enough to predict rotorrotational noise in front of the helicopter. Arndt and Borgman2 6 present a model fordrag rise harmonic noise based on profile drag on the blades. Profile drag Is shownto be a significant source of harmonic noise at high forward speeds, a source thatwould not be reflected in airloads from aerodynamic pressures measured on the sur-face of the rotor blades. Lyon, et a12 7, approach the problem differently by tailoringthe thickness distribution in the tip region to reduce noise near Mach 1. 0. Resultsfrom both approaches are similar, since reducing blade thicknesp -reduces nois-e (anddrag) and reducing drag reduces noise. In practice, Arndt and Dorgman's approachis fairly straightforward to apply if airfoil lift-drag characteristics are available.Available rcsults from unpublished Sikorsky studies show fairly good agreement withmeasured data (Figure 8) when noise from compressible drag rise is added to lioisefrom fluctuating airloads.
Drag near the tip of a helicopter rotor bladc during high speed cruise !s difficult tocalculate accurately. Torsional blade bending modea combine with flatwise and edge-wise bending and with rigid body flap and lead-lag motions to influence local angle-of-attack, drag, and noise. Obviously, unsteady aerodynamic response characteristicsof the airfoil also influence the drag and noise. Consequently, it is Important to
17
7 comp M~JTE7D WIHDRAG RISE NOISE
I -CcThWUTI*.D W."THOUT DRAG RISE NOISE
1 3 5 7
ROTATIONAL. INOI5FW HARMONIC
FIGURE a. CALCULATED AND MEASURED EFFECT OFDRAG RISE NOISE AT 180 KTS CRUISE
t.:ij**h..! fIi- S a I.' i'.Isv 11101t. isi not ne-cvssaIrily in .ccuraite representation
.,z ~ ~ ~ ~ ~ ~ ~ (j** t ~*!ii'i:t011Uti r,.-' w rira, uluing high speed cruise. The simplem~ dvtshv ~~mpov ;Iz~*fl~g( Iw ~vfle~tjji~teI i~I teasure'I noise atnd is useful
to~r thaut rea:Iw'n. More c()flIitlence ~toe bile (I-velUoiQ( in the ability of either virndt
:,no Il'rgmn':rs mtvthout or Ixotn'-; nme .thod to pri-diet high speed impulsive noise levels.
I-li~t, it-sts ocr -xin' tuntitl ~imuilatiumn- amre nevded to estabilish this confidence . W to
-I :..;vv. .u rtefineit priut-itiofl nit-Ilue. It is t(nceivabite that more sophisticated expe~rl-
-1tudivit, will find that vxi-t ing nioslvis have producdre~rasnableI csti~mates of t~he
- v;o'usti% proper ties without coirrectly modeling the actua~l noise generaitng pro-
;es:4v VI Afttuat ion AnI51i:II to Ot- cas (:if b roadbanifd rotor noise). letafled-estrimates
.1t hi..h ptidimpulsivie nut. e mviv tOwni reqjuire in vnti rtly nlew :inalvtleal1 approach.
EngJ4ine' Noise
!h! r"' ,'ucti' ,i Go-i~t-raulv:, 11le!iv'cItiptr. are powo'red'by hi mtrnaii combustioin u'r.:,ines which
li tI e)'id~pewi try till.n~ 111:611 d UII I ;torI S ; and avcvss.orii-s thrnLu,~h vairion-v
.,Laet-l's of skiftiiig. amndr'~e: Althoug~h tu:trlv lit-lictupte'rs utilizred re~riprinx':ting
vmh~~~iflts~~~ eityurn l:ifl :1:I.wrIlitulohu 'nginen. Th~~elr~re, the dis-
c.ussiol (if engine noise sources in this zetport hans Isen limited to tilrbosh-aft engines.
Turbine engine noise sources fall into two general categories: those originating out-side the engine and those contained within the engine. The first category includes jetnoise, while the second category includes combustion noise, turbine noise, strut noise(turbulent flow interaction), and compressor noise.
Jet Noise - Jet noise originates from the momentum exchange between the higherrelative velocitv of the exhaust gases and the ambient air. This momentum exchangegives rise to turbulent shear stresses which in turn produce pressure fluctuations anda radiated sound field. Thus, jet noise is gcnerated entirely downstream of the engineexhaust duct. Lighthill's equation 1 , 2 is generally recognized as a valid mathematicaldescription ot the phenomenon of jet noise. In Lighthill's equation the far-field soundintensity of jet noise is shown to be proport"onal to che relative jet velocity raised tothe eighth power and a characteristic dimension (usually the exhaust duct diameter)squared. As is indicated in lighthili's equation, the let noise is a strong f'Mctio 4 ofthe jet velocity. In typical helicopter application, the engine exhaust duct velocitiesat the exit are relatively low, since exhaust diffusers are used for maximum powerextraction from the engine. Generally, exhaust velocities from helicopter engine tall-pipes are less than 300 ft. /sec. At such low velocity, the jet noise levels are verylow and will not contribute to the overall engine noise until the other sources are ex-tensively attenuated.
Combustion Noise - In turboshaft engines for helicopter applications, the combustionnoise is the dominant source. This source of noise has been "discovered" fairlyrecently and was in the past associated with jet noise by investigators who found adeviation from the classical eighth power velocity dependence of jet noise (Lighthill'stheory) for jet velocities below 1000 ft. /sec. Bushell 3 , in 1971, presented evidencethat the low frequency noise which was unmasked at low engine exhaust velocities wasassociated with turbulence, internal struts, and flow through the combustors. it is notsurprising that this source of noise has not gained prominence until recently, as itgenerally appears as low frequency broadband noise peaking in the vicinity ofL400 Hzand is thus frequently confused with jet noise. -
Combustion noise is produced by the unsteady combustion process in turbine engines.Because the combustor airflow is highly turbulent and the fuel injection system intro-duces variability in droplet size, the combustion process Is, therefore, unsteady witbtime with varying heat release which in turn produces pressure fluctuations within thecombustion chambers of the engine. These pressure fluctuations propagate down-stream and give rise to a sound field.
Ho and Tedrick4 have concluded from extensive analysis of noise measurements madeon small turboshaft engines that the combustion noise is the most significant sourcefor these small engines. A simplified procedure for predicting gas turbine exhaustnoise related the overall sound power level to a noise factor based on the combustorinlet temperature, the combustor discharge velocity, and the effective diameter of thecombustor. They identify combustion noise with a low frequency hump, characteristi-cally at 125 Hz.
19
V
.. , t l £ioll W "i z o'i. * hcy :ativiiiiied iit) (I.-rive i ntndifled noii, fn'ctur by* n~ial ,iA1 ljz adh1 hi:i!hm pt titictihc, va tu.--tu-ailr ra~tio, con bu torei rs
A shb* lit vat iatl.ln ot eq. :n~r ~uation Ds offered :)y Nvitzvl7. in -Ahich the presd1u.-.-ilit It i!ii.'i.- tilt- L. :1 1))%- il:-tvtl-:it tilt 21 . U p(,wt'r and the- con.bustor inlet-tern-
P.*Cl:%*J1-t-o-:iZ 1J-.,i% .1t-tvivil-raiture racii dep'nulndene is oroppeil.
I ~e~t~t~ so IV W *'i-r4.tt o'ther fuorms. of varying con .iixI~y for the predlcticactwl~i%.iustioarahi t UI nci- tFJ I'.jlu-se $L~1 to hav- W~ voramon~n , 'wever, th.-it the Impor-
t-tnt a-irarnittt-r. are the. all- ruW raite, comibustoir exit temperature, and comnbuator*.- it pre~sure.
Tht.- .d~ovr citt~d provedure'4 alli relate tht. over.1il sound. powvr level to the com~bustionproev.-s.q A proctedurvtfdoes Iinot appe.ar to exist for coinpvttng the combusticn noisefirtcttivitv p~Attrn ur ,pet-trum shaIpe. In the reeently Vablished report describing EAlinterini predriction int-th'j-l for low'~ !rf ;uvcwc core e*nglne noise to be used by the NAUSA.1irer.-ff Noist:Pe Iii~~ctionf (flic~e, fluff, t-t al , SUgge3tedi using Demi and Peartts 1
itirectivitv vurve b~ase~d on measured! ifirectivities from .ieveral engices. Also, they.&,ree with Dunn and Pearti's justification for adcpting tilt SAE 12 spectrum for In-flight jet noise on the bas~is !hat jet noise anti low frequency (ore noise are d'ficult to,M!Patrate.
fIowever, K.14in, .et a11 f romn iinalyslds of engine data. have concluded that tbt, direc-tivity puttern of comblustion noise depends in the engine exit geometry. Thelir cdatadoes not show as steep a 7eduction in the forward quadrant as dces Dunn and PearV&a,:idthoju,;h bloth plavv tbi' jwak at or~near P-110 delyffes from the inlet. The Kazin, et al, -
ia..:ippear to rx, Ynore consistent with Strnhle's ;work14 , who concludes that the 16wirerjuency cenmbustic.n noise should have only weak directional tv.
Ilnrillv, Ka'.n, et al. and Picke't" conclude that the combustion noise spectruJm shapeWiii close lv follow the tut bulence %pectrum at the -entrance. to the combustor. Kazin's1Iatai reveal 'a broad peak centered Atbout :300 to 400 lIz, which Iis conpsistent withM-iihvws and Pe.caeLchioll', ;and ve rtainlv inure intufflvely statisfying-than arbitrarily:i;sigflifl it a jet nioise spectrum.
In sum.-Pary, it appears that vornbustlon noisL processes a're not aa yet fully understoodand the noise prL~diction nmths)dology Is not fully developed. However. several semi-empirical procedures have Ilesn deve~loped wh~ch give reaBoflably good agre-.ment withavailable test data. In pt~rticutar, the procedutre presented by Kazianet all3 , (similar
20
in part to that recommended by tiuff, et al11 seems appropriate for current noiseestimates due to its relative simplicity and good accuracy.
Turbine Noise - The noise mechanisms for turbine-generated noise are similar to
those for c-oripressor noise; i.e. , fluctuating blade forces due to rotor stator inter-
action and turbulence in the flow. Turbine noise generally occurs at a higher frequencythan combustion noise and includes tones and pseudo-tones as well as broadband noise."iT'e fundamental frequency for turbine tones is generally above 4000 Hz due to the high
rot:ative speeds and many blades of the turbine.
There is considerable broaderning of the "tones•, commonly called "haystacking".
i'his phenomtnon has been found to depend to a large degree on the relative axial loca-tion of coaxial fan duct termination in turbofan engines (Dunn and Peartl 0 recommendthat the turbine tone noise level predicted for the 47T6D engine be reduced 10 dB aorthis engine, where the primary and fan flows mix internally) leading to the conclusion
that this compoernt of turbine noise is strongly influenced by propagation through theturbulent exhaust flow. Also, since the flow leaving tMe combustor is highly turbulent,random pressi~rc fluctuations give rise to random perturbations of the vane and tur-bine blade loadings. In the ease of the vanes, this phenomenon will produce broadband
noise, whereas for the turbine blades it will generate narrow-band random noise whichappears as 'hay,.tacks" at'blade passing frequency and its harmonics.
Essentially, no analytical formulations for turbine noise exist, although the mechanismsare believed to be simi'ar to those for compressors and thus compressor noise method-ology can be adapted to the turbine noise case. However, there have been several
attempts at empirical correlations of data obtained in turbine rigs and full-scale en-gines. Early attempts by Smith and Bushell 1 7 related the peak broadband noise levelto the total mass flow and to a local speed of sound and blade relative velocity cubed.A similar relationship is given for the tone levels with the addition of a stator-rotorspacing term, although large scatter in the data detract from the usefulness of the re-lationship.
Dunn and Peart10 present a turbine noise estimating procedure which is eimilar to thatof Smith and Bushell. They show somewhat better agreement with data, primarily by Ivirtue of selecting comparison data only from limited turbofan noise measurements.
Kazin, et a11 3 , have attempted to derive an analytical turbine noise prediction methodbased on noise generating mechanisms studies for fans and compressors. Although
the procedure is claimed to accurately predict turbine noise levels, it is of limited
value for general use due to the detailed design and operating parameters required forits use.
Since it has been demonstrated that the noise generated by turbines is related primarily
to 1) a work parameter; 2) a velocity parameter and 3) blade row axial spacings, therelationships of Dunn and Peart1 0 appear adequate for rough estimates of conventionalengine designs, as their relation includes these primary variables.
21
tA,. 13 .'Ick
r * 1. aw i:: v..lC
*~ ~ ~ ~ ~ ~~I w :a I;~ 1l 4..vl' vi ival':.i.wl nn! .. A-r ~tI.. . ... ,..~ i.: ~.*I .~ a. fit ~ 14)a'0 IsO fl L'XpL'ri-
* . .~a. .e 3;,.. ..... .%* ia !3.' .I:g I3v'v. (lain sho w tol..i ve ) try,
a .d:.-aI- . ::a-l i 3m~ d)~ * ~ III.:13.s . In.O"'i bllonips in the frc!(uency
r.*~. t * ~.* :a~~ ~r.' ,~:U1I't~.I :3 in' ~flucncic's were
.,I t : -... ti l Ol* In lte OJ!':;: of fillinpre.-iscr nos m t s1 , 0
a::a~iA..a.a -. ::.a il* ~ noirt. mýIvie~ni. ins :are rotor/st~ator interaction*azl.I ~ tur. it. na.- A: ~ilt j 1a:aItl i. M. Al i ', att .. upls-roflW tip ~~~s orrs
~kJj ':;t~ I... u.h l. I.Ilael,".j~: lit Ow qe**.~d 1'uadran:t ai Wvell is in the iWet
Ii t3*n~r4 ..3.) i.. 1: - ~I:. I. :aappiail Iproliv 1 it-mkvul Wallijn- n'itse theory. n:i :i~ ~ iiI~t~'~~~*l( ~[. , ly I u- .Oul PXeIIt~;utln~s thL.4') to the case of*.'.3)*~flil3.3' :i~! 33.- . Ii: avva 3Iu s' tice aTi FiiIt-i-inifl ti)the baiSicecltua-
-- Ia i oi. ill 'SA :a I: 'l Cit., V. l~e l~i t,-3 -lta.1 I . ) g. t s~~I.I Il i ir. to .i ntludL* effac~ts- of un-.' .I.I.vaisr t-jkii .-,ti,- I.,~ w-'Ie '- grin; upp.l h-.min slatlir rows aind( turbulence ingestedI~.3 i. *.~m *..-Nafi I'ia iz I.- . unwk , ollil. ;.ddit-onal dtetails, such as
xil.-JIP'jla .1 'Aand %;sil ult' ana:~'trdd w~hvr E!ifilI as, ,,uc~h Los itiffusion thrrugh the
a '.).r:aIk:313i v g: Ip a l * U:~: " rifqii- h' Ir motaia inlputs 1.c., (i-titt&lded L.ign aInd
r 0u i:1 ..h3.: tOri.ieS t~n :arv g*333*r:a liv ;tvatiiabIe it) the astal~IIIuser, anti, there-
t~n; i rt~iI tnst3lbods;3y is-,* it ieele'opi-O. *Ihvx faaiilte the neiss:W to svra~.L :lI l3~*) .*a] i . jm.h~ . . lit -bA I'j...n -n d .a iv . -e rI llt ailva vni3 flh31I4 f i5.ofl -iimplu relationc.hips,Sfh Allval-'1 whic'h frtquir'(5 ojiii input p)owiar or prex~gure rise and discharge flow,
lij. *W .whi..0i;a"InI oios iunvolving ina:ifv jI r:m(turs,. such as that of Smith Ind
IloJ :11 wahich incl]ude.:: Indepundfl3eflL cLItn'ions11 for tonei an~d broadband componenits,rov,' -st'ttrar 'wparations, andl h~igh Mach numbei .dow effe'cts.
'lii:- procediure h.- b..-q iound to cirx3t: itec l! .w'zh tUr.~.i;k4;n .:at:irz .At r*ipplicatwl to the. uf ain Vtngint. lhn ~rb~c~~tr.::; Grta~ jXAi'zi-
hirodoo-tiiwtm. - iiicaillv, there~ :zr' f'xi a ptrs;:Lehe.s Lo rc'lucirng the no-ic~ trurn. turI~zne'*~. s i'lLit ll.ý ,ppronavik ini tý. irvdcie t-L- mi it-t tb- srurct hiv c~h.vs'4 .11 det fixI.4z
-or oix-ratis),. ~:f~*~r; I 13I l'tt(I';, L-111' ir %1L~d1,'a teelinOI',g%' h:.nA~t***; ld W~ith-
out rv.g' :rd to) nuj~ist at~~nd 1(, t!..refor., (cIflgý! in v-rg~re r..~~lparaint~cr!sfor reduringtn flt uis, 1A -:' s 'zi.xs ge.l-trzally i:Ut in ' h orn. los's in pi:rforrnuac.ievithevr as~ iriivasud~c %i:i:,ht a~nd :.izv or ic:atdfut-l :.0.nsumption. T1he siecond a.-sproach is in tho u9t- of ~avoustivalI~. treinfud "Ict.3 t..% :W!.*rnuaUn ~:d seratedi noist- Irv-visvous dibsip:Itioni This~ secon'md:p*.'.::n i.d 'e l -df-., t~ :nF;.iA pten..) -
Mm:ICT 'andI al-:.) r.'-'ults in j-- r. .:-*if we:ight duea -tt tiL, au.aJed mutcrials.
* jeluctjion of (onih-usi. 'in Noire' - In order to araintai.. lho mame powe~r output, theet::*iL(;,V through flth! omfnaitor ha,; it,.**t~i~d P. .r-e-nr, the combustor diarwitmt., rcanf ix: incr::zsel so th~tt the combjustordis-hargeý velo'-h; r:in he retiIeed to. ai Itiala.flow rate. It is for thi.i re'ason th.-It an annular combrastor Is cjuicter than ;i can-type.combustor and thu reverse :anrnultis roxbustor is tho Liest coinflgurrit on from an aeotus-
* heal point (if viw.Strahl t t su-gests that a drop in comibustor flow turhule-eeintensity would cause effc- tiuto nc~kse recductioni. However, actual comb~ustors .Iep'.nduponv a high turbulenct: leviei tor flame .Atniilization as wrell -_-. for bu. cevr perfoiri~:nace.optimilzation, HO somv fx-rforfliaflve petnatlt would hec evcpwtvc with reduced noise.
Moderate redu~iutl.n ')i engine exh:iust nflile has buen demonstratutd using :I(oUti-Ai litint'rsin the X1791i) uflgineli. Conventional tre'atmlent concepts were uhilzel anIti required lariebUaeking depth to attenuate the. low frequency tao1ie components. This results In signift-cant Weight :and space p~enalties. lBowes.- showed substantial reductionin tungine ex-hauust noi.;e by thoe a.ilditiozn.Of L long tre~derl tallilpipe which rediri'tct-ethe tuxiuSt
alip~ltly Upward awayv from listni~tirs andl thus a*.4n benefited1 fromn dirvetlonalitv effm'cis.lie due~wn n, hitowe-ver, indicate the incurred w.-ight And performance penaflnties.
It-itduio i'nn ofl '1turIine N~sism - l~W examining the impo~rtant jparam.. lrs governifig tur-bine noisie, it was futind that inc'reasing the 4paa'lng hettween ftlit. :ttor and atator siuigt~is the nmos't :ait railvv imethod for redutction of noise at thet source... Although this thui~aincrl!:uiu the !mvn;:th of the h~aft. the ansIlaoei:litt-t pformanve losms ii very Mlight.
P'ropi-r seI-ectinon of htadde and vane cousits- has Im-fcn itemonsivrated te, ri-due. flt- no1 isefrom turbofans 1)y pushing the. interaction rnodea; into cut-off. Tian asmect, of the Tyle~r-Sofrin *theeory-t% should! be eqiually' :pplieabllt to turblinesl. Another coti.4lvtcriot isflithe
23
* * . ~.i. .a. 'a a .*i.at.. ~ : fl~ati.~l I.wevtr, con.~.ithIra-.
* ~ : . ~ Lal ;~.' I. ~.A~4It. Ow11 l.2urlir.e At~ige Ouca.h
~~i ~ -. A .. , .L*I I .t .*... .. Ili,- taAaai f -Ul:r.-ant. sx1:yc. This approach is
* , t~. *ai' .: ~ ta!dI-. tha, -1,, .i truaiin.~iL ro"% ... d th r-luc d.
* c,- - I' t** !aa~Itan .. d-a I' .pj q'i LIC. A., iS tbal± case for
.~ ~ - 44 * . f ;A- ;If i t f. it a-!.'jp iA~twt~~4.n s~tmt nloise* *..t:.1a. .. . .. *.' ; r.,.t . Cie *t no;se -*cifiicaliy,
a*trulgif 13 .1 I.di Lw . 'I L ,Ii t1.. v*~ ~~:,:eat~ili- 04e Struts inlow- vvi'..it', .avi:w r:;tI,k-r thm.~tah~.. a:! ut 1: . i re bult in k-wer -noise. Simnilar)--
It :"I *.t AJ i: 3ai1.t1 .il l~ A 'Ir..,. 14ill a-LdUCt* tIajjL~tr,;jqi£ *.te~i JUUisL.
N;e~z'~ai I!.. )I thv tltw Livtsr the strtit wmay actur, i c'hange la th..* ~1t1i:;I~i;I~i; ;t;; £j:~;1; *Ait h t~ fitw. air za£I.Ir.4ý twist to the st zut may resv :tAt ?"All .... I %rdflit troanilju~itin and Itirnilnt nnise will also attenuatet~t II144.tf'41 I',~i r,'Iit f Itai* *li:.ta.:aa'' U1I I it. ctiflnum fllt.lht uf Qbi tr*-Ž;t-
a': n a . ' aL .11. 1-1 to! I - *I.1 ~t1 ..-1 Ow1 r.Ltv imt- bu il n.;4)f Ow~ three :m urv(e..S
Rtlaa'ict-tin -if v ~u . -, Mall. ý-.twlivs. havis Il'4iil rcof4urtt-d Ito alle'viate the."hail i - -t 1.91.1 st.a1,''s inl turhad-.inis t ý'9 . The rviiuuit Irmni these. -itudies art, eqjually
**'I. i ~.i~'1. I :~~('sL'oF ati:~ eaip Isos SignIfhvant refluttion can Ix.- obtaine'dIs-, 1i:( t~i it'!~I I spavihg Itl4Iiroitiar amnd -;tataur M tkfl(I toy rclt-Iung the ro tor
*i;;)r-.;.vJr fl'ijist is i~s,spvvi:aIj WO1 3il at.'IlU.Ii-te( lby :ari)11tical luilins: ;ni's~rials -dnce theI jla:.tj *.ai ;1 ri'l tistialI .~ . . it, I raIewI lit, nc:!. it prnipg~atinrg :1 ..w)t Ote flow,%fill t!wtet- irni tnpe'turairv is az.::r ;qnii~a ,wherv 1a'%;.; ex~~tje iaz jiitterial than th-ni.' iv-0
iR lifeit e.j .iau (I:( blot I ctiJI' ni e vXIa1:0t, ita, i1 the . for engine a'xLaus't treait-
f.:Il.)x.~jg is limIiiittalI, vilrv~~ .1- ill lt~~ Jt'I~i:i''.'It' frel it.eauy :ilnals nevur-rin41 A: 4-:101 temth bi .,,,'t*(r aist:AliiuaI,) frai-uatinry'k~I hii I 'Iaflit-1aii~ :;~.d-n. I'haw-
.n01r.1 ut timex*, 11:11, V.tlabit '-iaithhatiifile, which ari*t. g.*nerally lnxliznifivaint rvlative W(
tih :t- at m.eshing frequenci;s. Mesh frequency noise is ra(oiated to tl-.c atmospherebý lh- casing or the stricture to which it is attachcd. The r~diating body is drivenby the dynamic svswn' comprised of gears, shafting and bearings. The dynamic sys,
t.:m is .excltodiby !he rn.ihing .)f gears, which is Imperfect In all but ideal cases.lmnIM rfect mieshing induces :an oscillating force as well as the intended constant forcetra n smitted to the mr:nia gears. This oscillating fcrce.is the cause of gearing noise.Both the generation of mesh frequency excitation and the path It takes to the final radia-tion point must 1w considered in predicting and r(-ducing gearing noise. Both analyticaland empirical solutions have been developed for gear noise prediction. The analyticalform of solution, hov,ever, not only predicts noise levels, but can be used for Identify-ing means of noisc suppression at the source.
Empirical methods are gener-ally used for pre-diition of gearing noise emission. Thereare several practi.al reasons for the use of these simplified methods over the highlydutailhd analyses now available for transmi•ssion noise prediction. The lirst is thatthe analytical methods requirer a detailed knowledge. of both the design of the trans-n..,sion. and characteristics of the system, such as bearing load deflection character-
istics. The second is the tact that aircraft transmissions are designed with subst-antialcommonality in terms of loadings, speeds, and material-', Also, the normally coin-plex casings and airframe configurations do not lend themselves to dynamic analysisat gear meshing frequencies, thereby adding a significant unknown in terms of soundoutput on top of the problem of computing excitations andemissions from the basic.gearing.
Excitation of gearing svstems at tooth-mesh frequency can be determined through theuse of computer programs such as those descrifxbd in Reference 1. These progr"mshave been used in several studies which demonstrated that a reasonably accurate pre-diction of tooth mesh excitation and resultant system torsional response can be made."Thcy have bxeen improved and supplemented with lateral bending'anrilyses of the gear-ing system elements (References 2 through 5), but have not been integrated into a totalprogram which is capable of accurate neise predictions. R should 6e- noted, however,that the detailed analysis of References I through 5 has made it possibLe to attain noisereductions by shifting resonant frequene'fes of saomie components out of the normal
operating speed range.
The disadvantage of the detailed analytical approach to gear noise prediction character-ized by these and other programs Is threefold. First, the detailed inform~ation on gearquality ..nd the dynamic characteristics of some elements of the gearing system are notgenerally known and must bc estimated. This immediately transforms a rigorousanalytical solution to a semi-emppirical one. Second, the complexityof these methods
requires computer programs which are difficult for most engineering organizations touse without extended study. Third, the accuracy of the programs attainable at theprese.'nt time Is limited.
25
.;. .n .akn v~to Ox i anai tival procedures, tli-ire are grap~hical methods .ivail.labl!Jr 0.,- esliiw:.At'n of nlwsh frequenev excitation Wfich .iccotult for the impornant para-
:;.'LL~IwiLb~4pov.'cr trasmitctd,- tooth, loadwa,, pitch line velacity, toothl prcflletritooth protile roughrnLss, tooth spacing error, tooth alignmient error, p.th
c,)fltaict ratio, approach awlii ceess angle, prc,;surv an~gle and backlash. It Is felt thattrus peof pr-Aiicticmn, p~rLs:t:nlttd in Ittferentc 6i, is valid in estimating this excitation.K-ii-ve'r, an vajCi:allv important part o)f tw! :.!.i estimation proceS3, that of translatingthe e-xo~itji- )n iitar radiatcd noisev, is ,iuljjtct -., large vrror.
1' :-ansmissionl', and helicopter main tran~smis sions In particular because of stringent~e4tlini~t.&aiufs, are cornprised of many coinple x components which do not readily
lend;. *L.m~ivlces to dyN-amic analvsis at ine.'hing frequencies. The casings are probablyti.e ':.!t.fliiult part of the transtnissi-n to anal, zv U-cause of their complex shapes"'tl %ag~ ~a z% ing cross sieations. hlighlyN detailied arialyses. auc asth ntel-
i:*.pplro)awh, are netcessary to dt.fine impvd;Anc-:s and miode shapes.. Lacking 3uchanfll. SvS, empirical or statistical means are used to cstimate the casing's effect onradiated tLaisc.
The casing Bs tlec single- most important clement in the-chain of events leading to gearmevsh noise emission by '.irtue of its influence oin dynamic element mounting Imoedanceand It-i uLLtimate radiation of mesh frequency vibration as noise. The fact that nojI~z:-c tlcail anal,, sis exists for il-,rminlng its dvilarrnlc characteristics makes the emupir-ical approach to geartx~x noise prediction necessary for the present. although suchmethods are somewhat inexact.
Helicopter transmission. are de'signedi to transmit a rated power with minimum weight.Thbey are manufactured %ith a high de~gree of quality control and tight tolerances tomaintain safvty margins required. These requiremvints, along with similar reductionratios from engine to rotor on most helicopters gives this family of transmissionsenough comrnonality to allow a good dleal of generalization and an empirical method-tobe u~sed in predicting ermitted noise levels. A method such as this Is found in Reference6;. In tilis methudA, the rrvinufac~uring cha-racteristics of a gearbox are-used to classifythe .11d qs the sound ipowf-r le-vN of twnot-w Is plotted as a function of transmittedpower. Figure 9 shows the sound power level versus transmitted powuer curve fromReference 6. Since helleopter gearhoxexs are manufactured to high accuracy standards,their noise sh~ould lie In the vlatia B or C area ef Figure 9. Levels predicted In thisway appear consistent with unpublishied Sikorsky danta.
Meference 1; ak()o provjdt.es soni)c empirical inlformalftioni on the noise reduction that canh~e :a-hieved with various modi~fication~s to gearlaoxens. '1hcne are shown in T~able 1.(Note that the recluct bati for each variable ark- not necessarfly additive).
In sumnmary, significant proqre.49 has4 twen made in understanding gearbox noise mte-chanisms. 'l~his progress has included the development of both analytical and empirical
26;
160 I IllII i 6ýnd
are Ofg f•iid
C Reijt of eaxremoely W•h moan ioauring accuracy and
|. CIs C: 'l;gr, 'o•.! ,ctur•ng U¢"..,ce.
Closs D Nor'- -l qac u lity revqitd.I
"C 1u E: Gear •h-,s with high noise levels "at are easily
crec red by i, creairog the monufoct44mg q .ty. D
so I30 CC
1,20
110
1050 10 CI W 1000 5000
FIGURE 9. NOISE QUALITY CLASSIFICATION FOR GEARED SYSTEMS
prediction procedurea which can be used for new gearboxes. Empirical methods :re
relatively ca3s to use and appear to offer reasonable accuracy for gearboxes such as
the lightweight, highly loaded, close tolerance aircraft units used in helicopters. Ana-
lvtical method:s, on the other hand, require a great deal of detaihled design information
to use and still require some empirical corrections for reasonable agreement with
experiment. However, the analytical procedures do provide Insight into problem areas
and likely noise reduction modifications which.can not be determined with the empirical
methoda.
27
/
~4 n
r-..-. rr; ar !c LJ
•'.,,
i-t
j , - -', : °.
| . i, ~ a:.. .,
3. ...,
- I , - . $ .
3 ... ... I
* :.-4.-I
( . )
".:1 * *" :t , t• •,,2
- ).
24.-.. . , . .1.
• , ,: i*. m. . I .~.* •i i|
-*
.. . a e . -.
j j, g .:ll ,. II~a a k. * I j .I 12
3...,.,...
. i * 4 %*t I s , l , . ' .t •b
*i 11
• . .* .. . a.If ... . ±. . .*
,-I .. ".*" , i s ' ,•' *.Ir..
.* . .. ap
la.P3.I',.,
... J , .,. ~. -- lI" a.l'l"* i" I~t.a li 1
3.p-
; | I II,|,i a
Des~pite all of1 th.. work that has been dofle to dtvt-lop prediction methodis for the souircesuf V. STO *I. noise, alitemptb to formulate comprehensive metthods for prcdh~iizgn, thenoise fromn a eurnpletet vetacle have occurrvd oak; re-cently. The two m. jo r studies thatipecifit'aIlv :scr'hliapirare. reported in Refurences I. and 2. Boath studies dealwith nrdst- lruw. main rotur. tail rotor, and engines. Noise from grearboxes is ignored,which is a legitiniate simplifivation in most cases, especially at distances typical offlig4hts over porwhited areas. Re~ferenlce I consiaers the special case oif tilt-rotorvehl'dcLus, but uses Htht s~ame oredietlor. method a,4 is used for helicopters.
Both studies use the dlosed-form rotational noise miethod of Lowson and (iilcru-ad3
as the biest practical tool that is presentlY aV.'iil.leM. The selection of loading Uarn.onicdiway constants, called "loading laws". is Ihasid .)n acoustic test data. i'XcitIA~r ret:-
crence specifically duals A ith the effects of rotor-rotor inte rference on tail rotor noise,*since. relattively little information is available 1r. the liter;.ture. Broadband rotor noise
is predicted with emplrlc(i-at it, -ods. Although differtent studies are referenced Indeveloping the broadband method. both vehiclu nloise rtAIieods use forms of the so-called Scheh-gul ecluatlcii4 with a dlirectivityvcorrection as jpropbsed by Lowson and()llerhead. in ltt-ft-rence :1. Engine noise pred1ictlon also uses empirical proceduresin each methodl. A sample of the agreement obtained with the method. of flefderence 2is shown in Figure 10, below.
-95
90
85_j- MEASURED
IL- CALCULATED
75 I.A A A I I -A j.-
0 02468a 1Q.12 14 161Is20 2224 26 21330- TIME AFTER TAKEOFF . SE.C
FIGURE 10. TAKEOFF NOISE CORRELATION
The agreement between measured and predicted noise levels Is quite good and is ade-qiuate for us%! in stutiqs of community acceptance of noise using tone corrected per-
* edved noise level, lE1a. 1. Similar correlation has been obtainted betiveen predictedanti measured A-weighted sound pressure level , SPL(A). It is linporiant to note,however, that the referenced 'ehlcle noise prediction methods have demonstratedgood agreement with gress characteristics of the nolie, namely PNI. andi SPLIA). Cal-culation of more complex measures of subjectivc reponse Which may be needed to as-sesls tone content and impulsive noise require revisions to the referenced methods.
29/30
fl'.1.l( PT'(), R'.l NOIS.E jjf-H['C'fION TECHINIQUttES
o ri t,', 4o h.l i..pt,.r nuis,, rt-luires that all ol the s(,urces of roi:-e, including i nainrotor, tail rotor, engine', and to a lesser extent, gearlox be :considered. Studies offoist' sour,.,.s and. ih,.ir pri.ikction for .:ih of the.s. components ot dhe helicopter in-hc,..rntl. :adh'Vss fil. h t 4 14.1 rduc.tion quo.Ution, hint.e the irfiuence of .,perating ant!.on,:i.ur:ititin pa.n'iviers on nokise gem ration is part of any noise prediction technique.
i ,tl.r svetins of this rcpor! :4hdress the n:jise prediction techniques in detail. 'Th-Cre-1.;r ., in this -ii-ction orlv thi tioi:;e reduction tcchni';ues investigated experimentally
%%ill !,. discusz.-
()f li:'•-t intt-erst atv the noise rteduction 1xit.ri-wents conducted on the lIughes O-tGA,
the. :,korsk- ýS113) arin the- Kaman liil-.131. "h'l"i-t;A is a light observation heli-4 ý,)tcr of 951 kg 210.1 l.,rs j t.i4ibht with a fiur-hiaded main rotur and a le'r,
bladed tail rotor. The 1ll-11113 is a lar'ger helicopter used for Air Force Rescuemio.sons of 3175-4:30-t r.g (7000-9500 lbs. I gross %% i-:ht.with two meshing twit tadiltdniain rotors. The SlfalD is a large troop transport tpc helicopter of 70-0 kg 1h].511lb-. gross weight with five-teiaded main rotor anti fi'i-bladed tail rotor.
Anl'.: :3s of the ( )li-i;.\ no4).. signature as shown in Figure 11. from lReference 1) clearlvindw'atehi that main rotor. tail rotor, engine exhaust and gearbox noise all contributesub.stniallv to the total noise. In order to suppress main rotor noise the design tipspeed was reduced from 6;-i- it. :rsec. to -13.| ft..sc. In order to maintain performance,five main rotor ld:'hs wlre used instead of four. The main rotor tips were changod
from the standard r14.t.I:..Ular tip shape to a traipzoidal shape with a 2 degree twist."lTo !i1•p')rss the tail rotor noise its speed was reduced from 3120 rpm to 16:30 rpm.'o maintain performance, a lour-bladed rotor 14'. larger in diameter than the stan-
dard rotor was us.od. T'he angles between blades were 75 and 105 degrees instead ofthe conventional equal spacirig. Aibo, high lift eamheted airfoils were idsed insto.ad of¶ - the standard svmmuitricva airfoils. (;?ar'box noise was suppressbd by use of lower
pit( h gears with hi-ht.r contact ratios. These gears were also machined to higher-accuracv :.nd had lx"tter surface finish than the standard gears. . Damping materialwas applied to the w,.bs of some gears and to the core of some drive shafts to reduce
ringing nois|, resulting from gear clash. Modifications to the engine as well as exter-nal muffling was used to :uuppress the engine. rhe basec engine modifications2 consistedof i) shot p'-ening the first itaqv turbine nozzle to create a :ionic inlet block; 2) hal.maningall rot:nting. ompon.*ntst i to cu.,r than normal toltehr-aces to reduce vngine casing vibra-tion anud .3) clipjpivg .. 'v al s:tagis of compre;sor vanies to Increase blade./stator spac-ing and thus redluce- inlet .iren noise. tlss: engine changes resulted In an exhaust peakreduction of 2 dill. The ,irwine exh:tuSt inuifler consisted of a tuned douhle expansionreactive type muffl,:r exiting ;nto a large tun, -1 resonating chanmber". Engine inletnoisc was suppressed by lining the inlet fairing and plenun chamlxr of the test vehicle
with 1-inch thick oro-n .ell polyuireth:ne foam. Peak attenuation of engine noise wasfound to be over 30: d1l for this system1 .
31
"r':Ac .arly test Lczfort.; on the lIi-4:3I indicawa that the rotor engine and gearboxnScu!:r:Lutc'd to thu !oise signature. Enginh. noise con.ponan*s are inlet radiated broad-ba~iii fUw noise and discrte tone compre..sor noise, case radiated mechanical and.jnhbustiun nodise, and exhaust radiated broadband flow noise 3 . Inlet noise was sup-pressed by a revers-' flow inlet duct, as shown in Figure 12, with a multi-layer :e-activý, liner. Ca,:e radiated noise was suppressed by Installation of vibration isolatorsbetween the engine and its supporting strueture and by a high transmission lose enclo-surt- around the .n.ine t omp:trtment. Exhaust noise was suppressed by the exhaustduct shown in Figure 13, which includes a lined absorber section for attenuation of
nghIne and in--duct gener:xted noise and a diffuser section which allows for uniformexpans*onn of vxhau.;t gases to nearly zero relative velocity. Additldnal reduction isachii.ved by directing the exhaust nearly diretctly aft as opposed to the downward
directed exhliust ofthe standard aircraft.
it was found tLit the vibration isolation and installation of an engine enclosure were noteffective In reducing the aireraft noise signature. The Inlet noise suppression waseffective, particularly the suppression of the compressor blade passage tone. Reduc-ticn of as much as 10 dB In the mid-frequeacy range was achieved with the exhaustmuffler.
Many, changes were made to suppress gearbox noise discrete tones at frequencies equalto the gear clash frutquency and Its harmonics. These changes included the use of agear set with good wear patterns tand minimurm tolerance, plating of gear teeth toimprove surtace fitush, the use of high viscosity oil, mlsphasing of right and left drivegears, elastomeric !..olation of the planetary ring gears and Installation of externalsound proofing. -Octave band analysis did not show any improvement for theae changes.Hlowever, the changes did re:ult In a subjective Improvement as they reduced the levelsof the discrete tones in the spectrum. The external sound proofing was not effective inreducing aircraft noise signature.
Rotor modifications included increasing the diameter from 47 ft. to 50.34 ft. , Increas-ing blade chord from 15. I69 inches to 18.69 inches, thinning and-drooping the leadingedge, and slightly tapering the tip. These modifications caused a reduction of higherfrequency noise components, but an Increase In low frequency noise. Reducing the tipspeed from 540 to 4f2 ft. /ceC. reduced :,ise throughout the frequency spectrum by 3dB. With the reductions achieved, the rotor was still the dominant noise sourcethroughout the audible spectrum.
Initial analysis of the S!,21 .,. dlcated that the total etera-l noiac spectrum Is domi-nated at various frequencies by the main rotor, tail rotor an] engines. Main rotor andtall rotor rotational Poise at multiples of 16. 9 and 100 liz, respectively are dominantin the low frequencies with a mixture of retor and engine noise contributing to the midand upper frequencies.
32
A .1w. aonola
I, is, -,
-10 M - 10 SAI
M^11 A19, I
F sminan
C;A' I G.
?AIL NOIPE - A&ELL1 ~~~~/ IN. 4r,,,J 11/2 Is. smCELLs n CL
3/4IN NUITC. flIN. 3.".FBRLS
~~~FIGURE 1 3. OEALNIEXHAUSSN IUR 2.ILT SILENCER CNTUTO
IN HOER (RONTVIEWAT CNSTRCTIO
*main rutor noi.-, was treated by reducing tip speed from 662 to 597 ft./ -et. and cha:.g-in; from 5 standard i-;quare-t:pped blades Go six twisted trapezoidal tiu blades. Thetall rotor was treated by reducing tip speed from 657 to 442 ft. /sec. and by doubling.the anaber of blades from 5 to 10, Further attenuation for cruise flight was gainedby mondifiing the aft vertical pylon to a cambered airfoil configuration, thereby reuiov-ing some of the anti torque load frornn the tail rotor in this flight regime.
l'h11 1AIC;.ines were attenuated bv inlet and exhaust silencers. Although the silencer per-ref~innce, was not measured, on the engine, tests with no flow showed peak insertion
loss uf approxinmaiely 25 dB around 1000 liz.
X comparison of roi.se generated by the standard and modified helicopters showed thatnoise is-at.tnuiated at nearly all irequencles with the most noticeable change occurringat the tail rotor blade pa'.,.; frequency. Tail rotor noise was reduced to the pointwhere it was almost ir •i dlcant for the modified vehicle. Also, high frequency noisecomponents were rec!,ced by 3 to 10 dB over a wide frequency range.
Although it could not be shown In the 1/3 octave band spectrum plots, the character ofthe noiseu'was entirely'different for the original and modified aircraft. The standardSH3D was easily identified as a helicopter by its characteristic main rotor rotationalnoise and tail rotor "buzz". The .modified SH3D sounded like a low speed muffledturbojet during flyby4 .
Noise reduction methods described above for the three helicopters involved in the quiethelicoptesr program were for the most part, straight-forward techniques with proveneffectiveness. Rotor noise reduction was attained via reduced tip speeds, increasedsolidity, and limited blade aerodynamic improvements. Engine noise reduction wasattained primarily by muffling. Gearbox noise was reduced primarily by shieldingand damping.
The techniques employ .d were effective, but reulted in performance reductions andweight increases in agencral. They mrove the helleopt.ra' op•ratlng, parameters awayfrom those which were orig-inally setected on the bisia of performance and economicconside rations.
Further research Is requlrcod to define rotor and engine configurations which are bothquiet and efficient.
34
SUBiIECTIVE RESPONSE TO HELICOPTER NOISE
Introduction
For more than twent\ vears efforts have been made to develop noise rating scaleswhich accurately predict the subjective response to aircraft noise. The difficultiesof corducting meaningful tests, where the results are determined by listeners judgingvarious sounds, has led to c'onsiderabhe confusion about the relationship between onerating system and another. Also, there arc two distiact objectives which must beconsidered in developing the rating scales: 1) a scale to measure the perceived levelof an individual aircraft flyover sound which can We used for noise certification and2) a c.)mmunitv acceptanve cah'ulation procehLre which accurately evaluates the longterm effects of aircraft noise on communities around airports. In the following dis-
cussion, the work on various units for noise ct.rtification and community acceptanceof helicopters are discussed. Then, the direction for- stablishing better units forhelicopter noise assessment are discussed.
Noise Rating Units for Helicopter Noise Certification
Background - At the present time, most noise rating methods are based on PNdB ordBA. PNdB Is a computed unit based on sound pressure level and frequency for one-third octaves or full octave bands of noise. The dBA may be read directly from theoutput of a sound level meter having an A-weighting network. Several researchstudies have been conducted to establish the relative merits of these methods as pre-dictors of amnoyance. Pearsons evaluated subjective response to recordings of bell-copter noise in comparison with transport aircraft noiset. He found that PNL wasslightly more accurate than weighted sound pressure level such as dBA, and that adjust-meats to PNL for tones and duration did not improveits accuracy. Hecker and Kryter 2
determined that tone corrections below 500 liz reduced the accuracy of various unitsand suggested that the use of tone correction for low frequencies be deemphasized.Ollerhead3 studied the subjective response to low frequency high intensity noise. Theannoyance curves he defined departed from existing curves below 1000 Hz. Figure 14-(from Reference 4) shows that this is significant, since the large amount of low fre-quency helicopter noise is the main difference between helicopter and other aircraftsounds. Sternfeld, et a15 compared response to simulated helicopter noise, tilt-rotornoise, and jet transport noise, and found little difference among peak values of PNL,dBA, and dBC as annoyance predictors.
The work by Ollerhead 4 , 6, 7 Is considered particularly significant in establishing thestate-of-the-art in noise rating scales. In his work, a fairly extensive experiment wasconducted with a large number of aircraft sounds including turbojets and turbofans,piston engine propellers, turboprops, and helicopters. His most recent summary ofthis work6 contains some surprising conclusions. First, It was found that all ratingscales are equally poor In rating helicopter noise. Second, an integrated duration
35 ("
4I
0]
-30t
!-I
-40 1I
(c• Jets•.• -20--.:
-410 .I ... I 1 ! I
.063 .125.25 .5 1 2 4 8
Frequency -- kHz -
-10
(b) Turboprops and Pistons -J -20
-30
-40 " 1 1.063.125 .25 .5 1 2 4 8
Frequency - kHz
0
-110
(c) Helicopters -20
-30
-401.063.125 .25 .5 1 2 4 8
Frequency - kHz
FIGURE 14. "TYPICAL" 1 3 OCTAVE BAND LEVEL SPECTRA FOR DIFFERENTAIRCRAFT CATEGORY SOUNDS
36:
correction (as in FAR Part 36) is particularly beneficial, probably because of the longduration associated with some of the very low speed flyovers. The duration correctionbased on 10 dti down points (i.e., as 10 logjo (t/15), where t is the time in secondsbetween 10dB down points) was sigrificantlh inferior to the integrated correction.Third, the simple energ), summation process performed by the weighted sound pres- :1sure level circuits is rather sensitive to the particular choice of network. Thus alinear (flat) weighting function overestimates the perceived level of an aircraft sound,A-weighted level underestimates perceived noise, and D-weiglhted level (based on the i-.inverse of the 40 Noy contour) shows a very small mean error. Fourth, the ton!- cor-rection used in the EPNI. proc,.durv does not perform as intended, except when appliedto turbojet and turbofan sounds. It is recommended that the tone correction be elimina-ted !ri" tones identified betow 500 11':.
In anoth¢r reci-nt study, Sterafelh 5 found that helicopter annoyance was under-e-,timatedby .44.1 PNdP compared to jet t:ansport noise annoyance. For example, rotorcraft noiseat a PNL of 94-96 was rated equal in annoyance to jet transport noise at a level of 100PNdB. Leverton8 has studied helicopter noise extensiW'ly and finds that existingmethods are inadequate for rating helicopter noise. This is true for low frequencyrotational noise components (including tail rotor) aa well as for impulsive noise.
An additional source of inaccuracy of existing Perceived Noise Level and A-weightedNoise Levels is their inability to rate impulsive .,otor noise. Relatively little quantita-tive testing has been done to define human response to repetitive acoustical impulses.Munch and King 1 l surveyed the literature during a study of community noise accep-tance and found that the presence of impulsive noise increases subjective annoyanceby 4 to 6 PNdB. Consequently, considering the findings of Sternfeld1 2 , the annoyanceof helicopters with impulsive noise is likely to be underestimated by 8-11 PNdB com-pared to the annoyance of conventional transport aircraft.
From the preceeding discussion, it is apparent that existing methods-of rating hal--copter noise are inadequate. Shortc6niingsEarLse from the frequency range of the noiseand from the characteristicsof the acoustic waveform. A new unit or new units arerequired in order to accurately predict subjective response to helicopter noise. Of theexisting methods, however, no one unit is clearly superior to the others.
New Rating Scales For Helicopter Noise Certification - Based on the deficiencies notedabove it appears that a new noise rating unli is required. The new noise rating unitoutlined below is intended for noise certification testing of Individual aircraft. Itshould be emphasized that instrumentation and data processing for such testing are elab-orate and extensive compared.to facilities for monitoring and evaluating communitynoise levels. Recommendations are made In a later section for a community acceptanceunit that parallels the certification unit.
37
M 0.4. :: t Ii~ vf!~s c:cal~wit Liflit ';itU. *.. av-.A.L ki.!
~~e .i.h~i*.~Crsonst, curves thait e~tw*Ld. Lelow,50 liz aad cover
- .,,,t~~* *i.) *Z. 1:rc .t M~~~~~ I'All Pal E A1 rathtcr tha~n ceorrectivlls
till Itl.. !1;11t ,dt I '-L 'f- Li±: it) dli *l;.r polints,
3. j,.ri~ . 1AIi(altj fM i t:'. 1.r'.:t oi if:,lub.iVL nloise..
C. ~l t .;.~:( ,li-:-rt frrquenc~ius t~hat ad.e~cjuutei/, represent human
11 at a :d' ,k~~ to -;n-c-it\ ho Id:., urit will LK: .ce 1I:~. Ps.ehoacousttlct4~~~~~~.1h., sl4*,u~~1~i ~*ui.I Otiaif~icu1lies, s*;itL sU1i mi~ul.LtiUf at IOW
kict:qjve' teS.-;. II *cuILr the~ i.se of actual helicopter fly~n ers (as opposed to r'e-alr~n!ifi(I ., toa-: Lpc s~ ure dthtat i of the- spectrumi chiracteristics and psycho-
I:41:L (!*(-L.t l .11 re accraktt presenited to the listener. durntfts proram.
Commtunity Ac~ceptant.e Calculations
t.i:r.,ua Tl- t nsI~. ;.~e~vt: o~f noinec~ rit'-ria to which a Lclicopitt.r wllI W. sub-;j( .cld :tii.c Vretifaevatz'n .. cd(oiflfiuniiU acceptaince. Certification criteria define thenliru-e Ui.11 t;*.(- V.hivitc will IM~ alloviet to pgeneiratLe for typicat a keuff. landing, and
:im .. t.p4eratiorls. (ommzunitv atrviptaifce criteria relate'this i er~tlficzAitin noise to'V01i1i1ia.11ljty Ii~ 6l..Iylf' the toital t.ffet' tsof opcratting IY:3nIV t~vptN of alrcratft for
rnuhtipli* Ilight~s at vairi',u- tix~otvs of the day owv(r or into various I)I of the community.
jlit. iI.-terfl~na' 10,t Ofl:I~:dt comintinitv ;icreptance (if tioise throughiapplication of.,.t iv. fh(:l:I 1:,r-.-wuir. 1-'ir.inidunition ot ai large nu ' r.,xr of eI.!mvwixts. It involves
'?-!1Ilii: Lilt! Ia161t i1-v f~u liv mvuiv lu of v.IrviagAircralt tvpt-s using znarny- ,1~1j~.;vh "~ab~o~ path1 )i .t rive ..I. .a Iil:a* expio ure numbewr whith Is de~sc:riptive of-
.:i Kff~lof Iurso --;.i::. Tlhd.s 4- neft ifI-i alao influencce-Il y the' time (it day at
Oduih [Ill. it- 4si' orrur, I he 1%i ' . oaf coniaaaunity in which thily occur, aund in nlihflV cases,th :,nIIIaItit foaIs; le-vels gazw crat.* by soures othe;r th~an airt-raft in flt! area. Thefol lowing disvusaton va::h',ate-s tin randidaule imncthi,'I for ratittoj~0~:!; t of ioiweunli ,..1~~tvc; ths bivna' thimi-4l~h It "it-licptc~r ni'E!,4.
TI1Mle 24 It"JUI- till rcF,: t'- ru.-pOt liyl~jt, or~a~ and He rniOOedI, staaitt; nr~iyv thti far-tilurs cgain:,aalsa. *t in Va c'EIjUS ( OfoanaunltitV uiso r-t lug Tit(ih(osbI. Till wm!o o#t 1. as1 theUnit I 'r ctilnamo'ijritv auco 1.1anck! vvaluaution of liel ivr.Iars it: reuttnueItyl I lintierkeutter
.111 -:t(.5flftdI I:i1)i:L it ill liuadas dvt-uneijflilItr.itiofl of tlt. ;.41.1,ita't neu.So* In thec voni-
3 1'4
TABLE 2. FACTORS INCLUDED IN VARIOUSCOMMUNITY NOISE RATING METHODS
41I 4i ii A) il
FACTORS $ > o
00 4 40 0 o
Modo 4u wd Vin d-A Level)- 44Compsit 0os aR 0B C Ca im(m
R0in FAR 0~d O- Leve0 0 0ommunityj Nois •E dB-AergEqialn Eeve 4 Energy
torec4)st 4 EnrNAME H U E-E 4IZ8C < 4CJE-4H U
London Guideline dBA •N/Level
Composite Noise CNRC dBA EMaximumRRating CNRA PNdB w 4 4 Level
Community Noise CNEL dBA AverageEquivalent Level Energy
Noise Exposure NEF UNZd TotalForecast Energy
Weighted Equivalent WECp!4L EPNdB AveragePerceived Noise j j 4j j EnergyLevelI
Noise Pollution NPL (a ny j jverage
Level Energy
Day-Night Level Ldn dBA A • verage
I ~EnergLocal "Nuisance" - maximumOrdinances or Level
SPL
Single Event SENEL dBANoise Exposure /Level
39
1'41Itt tII ult. di.,iriijution of noise± mizd number of flights per hour. Tlit*!d I.~t "it that of~ Wis~v r lB for ni ht time o artnon may b o mU
liee ra bea to malC. A10'1.L (3'ti.c- OWmpldint.; are. associated with interruptive. factors such ast v t:ccnt L d Mh.itr~ whlie nigrht time complaints niny be asiociated with
01- U1P I !,V t*Viti.)j3 -it SIccJ.
in -tn:)1h,-r *recmnt rvport bv Munch and Kiing t L the Ldjn conccpt is. endorsed with someia!. :111,0. I hey r-etimtndn~( thait a ptfraltt of. 5 to 10 d13A be adde'd to the. single
t'.*n V1 'i~ 11l-t: vNuJr4- leVVV ISE-:NF 1.) for a..a irvraft producing impulsive noise. Thisis: 'in: rinit with the lli:nterkevuu-cr arid Sternfuid1 0 fMAdlLý's. Mlunch and Kingk 1 aisorvivoinnit-nd the ustl of tunie cirre~ti1ons to the SENEL as calcutaied for Tone Corrected*.y-c~eivt-cI Noise L~evel, but univ applied to tcnes above 500) lIz. This is In agreement
v. ath (AlerhvtO.a.
in ,uflitnLi-y, it appoarh that Ldn with significant modlfic'atalons is the choice for corn-*miunitv ac'eptmnct- ev~aluation 'if helicopters.
Nia nits for Comnmunitv Accept~an'ce Kvaluatlon - As statc~d nIerees1ad11
(:rjli i.Mnitv :eeetarxu criteria ir-unst inelutk-t-lie aunbicmt notse riwlirotmnentj and shotuldbe_ reasonably easy to use. Kt is-elear 'hat existing weighted sound pressure level andiorceived noise level are equally good. (or equally bad) as predictors of annoyance andlt-.f('i.,nmmes 10 :and 11 revommiiend use of Day-Night Level (Lazn) balsed on dBA as a(-ornfunitv :acceptaflct' unit. Thel Lcln unit recotnniendedIn, Reference 11 uses theS-NE 1. unit, dilA vorrectc.1 for pure tones and dluration. Of cou 'rse, there io noreason to ;:s~u.1ie that a nvw -xvighting network or a new EPNI. procedure couldnut be used~i in Jpl:Iee of dBiA to Wiprove the -accuracy of the 1*da unit. The new networkWtOul( includek revi .Nel. exterglted low frequency characteristics patterned after the sub-jiective respotrise! re'sults discusse~d eatrlier. It Is possible that a revised N-weightingnetwork (the N-weighting avalo is somt-times referred to as the 1)-scale and 1istheinverse of the Ifi-noy vontourl would be .preferable to a revised A-weighting network.Nala uralilv, inmpul:we penahitue:- and tonle co)rrie'tions paitterced~ after the new certificationanit wo)uldI he usriI in thi- uvw community avevpit.knev unit.
*l0
CONCLUSIONS
In general, it is concluded from the study reported here that significant further effortis needed In all areas of helicopter noise prediction, reduction and subjective evalua-"tion to approac. 41.. , .. a .... achieved in turbolets and turbofans.The single area where the state-of-the-art is nearly adequate is in the turooshaftengine. Here, because of the interest in core engine noise of turbofans, substantialprogress is being made to understand the mechanisms of noise generation and developnoise prediction methodology. It Is true, however, that this new understanding hasnot yet been incorporated in any existing turboshaft engines. Therefore, the resultsof the learning from the current work will not appear until a new geueratlon of enginesis designed.
Gearbox noise has been studied both experimentally and analytically with some success.It appear that the tools for prediLtion must be tried in a quiet helicopter design toestablish where th current methods are deficient.
In the rotor noise source area, existing prediction methods appear adequate to estab-lish general trends or gross properties of the acoustic field for most common heli-copter configurations. Tandem, coaxial, meshing or variable geometry rotors mayrequire further study. From 2 more basic aeroacoustic standpoint, it appears thatthe basic theories now in use should be checked carefully against noise generated byhelicopters in flight. This will require measurement of aerodynamic inputs for thesepredictions. The oubjective of such a program should be a careful study of cause andeffect in rotor noise generation. Tail rotor noise requires this same attention, partic-ularly the evaluation of interference between the main and tail rotor.
While it is not likely that a commercial transport helicopter, designed with communityacceptance as a goal, would ever produce impulsive noise, work is required to definethe design boundaries which will insure that impulsive noise .s not produced.
Noise reduction of complete helicopters has -only been demonstrated in ways that reduceefficiency. Increases In weight for the modifications to date have been unacceptable ina commercially configured vehicle. Work Is therefore required to develop noise re-duction techniques with minimum Impact on perfoa mance.
In the subjective evaluation of helicopters, further work Is needed to improve theaccuracy of the existing units. Improvements to the EPNdB to account for the differ-ences between helicopters and other aircraft are required. Some of this work mayalso be applicable to community acceptance evaluation procedures.
41/42
APPLIDI.X ACA.P:,ULE REVIEWS OF SELIC[ED RElPRT¶
Rotor Nolie Cap-;ule St.;-Zries
.A 'ndt. R. E. A and B:rdr-ntia D:. C. , "Noise , adi'tiuin from ilei•c:o;ter Rotors (jIerat-i.z at Hn!.:h 'Tip Mach Number". Paper presented at the 26tn Amuial National Forumcri ihe American Ihiiucopter Society, Washingtcn, D. C, * June 1970.
The purpose of this paper was to present the resultz; of an investigation of high:,iach nunmber effelts cm the noise generated by helicopter main rotors and ti, reviewthe role ol drag divergence and biade thickness in the noise radiation foom rotorsoperating at high tip .Mach number. A matht.matical model for rotational noise wasdeveloped based on an adaptation of the Gutin theory to the case of non-uniform inflow(more specifically for the particular case of non-uniforrnity due to drag divergencecaused by operation of a rotor at a combination of high tip speed and high forward.sipcid) and utilizing publiLshed drawg data for symmetri..al airfoil sectious operat:ngthrough their critical Mach number range. Application of the mathen:-tl'cai model tothe case of rotors tested in the Ames 40-by-s0-foot wind tunnel gives good agreementwith the observed tremendous increase in the Ievel of the higher harmonies for a smallchange in tip Mach numixer.
Su.rnmarv
The paper reviews several classic approaches to the calculation of lift noisegenerated by a rotor including those of Gutin ,Garrick and Watkins 3 , Schlegel 6 ,Lowson and Ollerhead7 and Loewy and Sutton1 0 . Although each of these approachedthe problem in a different way, the results in general were not satisfying. A briefreview of other sources, such as broadband noise and thickness noise, completes thebackground on helicopter main rotor noise sources.
The mail purpose 4•f this paper was to reviewthe role of drag divergence and bladethickness in the noise radiation from rotors nperating at high tip Mach number. Theapproach taken was to modlify the Gutin theory for non.-uniform inflow and consider aparticular case of non-uniformity, namely the drag divergence due to the operation of
a rotor -at a combination of high tip speed and high forwaird speed.. -
A Fourier series expansion of an assumed pulse loading is used in the developmentof an expression for the harmonic thrust and torque coefficients. Following a develop-trent of the velocity potential for acoustic radiation based on Gutin and applying severalsimplifications, the rms value of the nth rotational noise harmonic Is given by theexpression
- )nu W ( rcos 6 4 b bM-- sin
n b•an M. J bnj e
*The nvmbera refer to the entries in the appropriate section of the REFERENCES.
43
where b number of bladus
W - rotational speed of rotor
r distaoce to observer
a, speed of sound
. Fourier coefficient in blade loadingJ
T thrust
angle between thrust line and observer
-- Fourier coefficient in blade loading
Q torque
M - Mach number based on effective radiuse
R effective radiuse
For uniform loading, all components are zero excepi for ao I and Pia = I whichreduces the above equation to the Gutin relationship.
The drag rise experienced by the advancing blade of a rotor wben the forward speedis such that the tip Mach number exceeds some crit. .1 value is a form of nmo-uniformityin loading investigated in the next section of the .- ,pe " %fter drawing a simplified ex-pression for a drag rise coefficient, CD, It is expaL~ed !nto a Fourier cosine eriesand the results substituted into the modified Gutin -; 'a for rotational Cibe.
As an illustration of the sensitivity of the drag Increase to Mach number and theeffects of tapering the blade tip, Figure 1 shows the calculated drag rise coefficientplotted as a function of the rotation angle (where 90 degreee Is perpendicular to thedirection of flight). A large increase in drag is shown for a small cnpge in Mach num-ber.
In closing the discussion, the authors present a few sample canculsUmsn for com.-parison with measurements conducted in the Ames 40-by-80-foot wind tunneL Two
- comparisons, here reprodiced as Figures 2 and 3, illustrate the comparlson betweencalculation and measurements for a relatively low tip speed, where drag divergnceeffects are small, and a,' a higher tip speed, where the drag divergence effects becomesignificant for both a standard tip blade and a tapered tip blade. Altbouh the resultsshow a large discrepancy in the lower harmonics, the tremendous ineresse in the higherharmonics (about 20 dB) for a small change in Mach number is well predicted by thetheory developed by the authors.
The authors conclude that drag divergence cdn be important for Uip Mach numbersabove 0. 85, sources other than rotational noise contribute to the higher harmonics,an improved analysis of vortex noise Is required, thickness noise is Important only forthe lower harmonics, and the use of tapered tips appears to be a good way to reduce the
noise at high tip Mach number.44
'i iTAN.OA T.-
'4 /"
• .i'Jt~.AN•GLI
FIGURE 1. DRAG INCREASE DUE TO COMPRESSIBILITY EFFECTS
SOVI IAL. LL.." L
;*"A A:. tA12 S.
0 ACe xT UAI.
':I.IAL LrbtI -" p I.XPV..0I.SE• Op eioar0ctfr-n.
tL" A A.
':~ I TbI•
rIf ~
,A; IS1 OA .16xP4e l16 L .1 r
I .A 1..as0.120
f 11 " M1
FIGURE 2. SOUND PRESSURE LEVEL FIGURE 3. SOUND PRESSURE LEVELSPECTRA, THEORY VS SPECTRA. THEORY VS
EX PER I MENT EXPERIMENTSTANDARD TIP S LADE TAPERED TIP-SLADE
(Clomprislon With Smnlll:jr Pape'rs
hi.3 plpo'r pr.!;ents a maihematical model to explai.n the substantial increase in
the higji'r harnioniuc uf rotational noise oh:served in holi,.opter main rotors op4'rati•g
at ; m rcbination of hi.'h tip spi'ed and fo•nvrd lilht. vhe analysis presents a cloted
form s;olution has',- oi Q i -u m;.p4unltionmt of -a periodie change I bil:ide loading due to
,ompr- .4sbilitv exffe:t't e xp*rienced by the bMade advancing into the flow.
Others have attempted to vxplain the increase in the levels of the higher harmonicsdue to non-tiuiform ltdi,'4 of the rotor blaidrws. Schielog-, et all' uiect a similar approach
in extondt-g ( ur in'.- :tn:i mlvsi, ,ir,:tly to the .:t.-, of non-tintform Wlade loadir. Th]ir
expression, however, is not in closed form and a computer solution is presented which
requires blade loading as Input.
45
Comparison With Similar Papers (Cont)
This paper approaches the problem of impulsive noise due primarily to a fluctua-tion in lift noise, in contrast to Lyon's 2 7 analysis to explain blade "pop" (i.e. , soundgenerated by the compressional wave patterns that are produced at speeds near Mach1) in terms of the fluctuating thickness noise caused by the periodic change of therelative tip speed of the blade advancing into then away from the inflow due to forwardmotion of the aircraft, or the blade/vortex interaction work of Widaal12 2 , Leverton 2 0 ,and Filotas 24 . It is interesting to note that both Arndt and Lyon show comparativelysimilar agreement with the same test data even though Arndt attributes the impulsivenoise to fluctuating lift and Lyon attributes it to fluctuating displacement due to bladethickness. Neither Arndt's nor Lyon's analyses show excellent correlation with thetest data, primarily due to the neglect of other sources, with Arndt underpredictingat low frequency and low tip Mach number and both tending to overpredict at highfrequuency and high tip Mach number.
Evaluation
The approach is sufficiently simple and stralglt-forwardto be readily integratedwith other, established rotational noise prediction methods. Compressibility effects,however, may also result in other noise sources, such as the so-called Imzzmaw whichhas been observed In supersonic tip speed fans. In this case, the rotating shock be-comes a source of noise in itself, as well as causing a change In blade loading. Fur-ther, periodic blade loading may arise due to vortex interaction. Thus, afthough thetheoretical development presented in this paper may be a valid model of the noisegenerated by changes In. blade loading due to drag rise, it in itself is probably not acomplete and sufficient description of the sources of helicopter rotor impulsive nol.This is, in fact, supported by the comparison with test data which shows only fairagreement in absolute level, although it does show reasonable agreement with the trendsin noise level with tip Mach number.
46
(,uxV. It'. "Suhconmmtte'e Chairman's IMnort to Mexhbershin on Aerot .stamic Sources
x ±•.o.t,. :zi.e, Pce wntvd to 21th.Annual Furuim, Ameri:.in Helic;•ptzr S-ckletv,M.l 1972.
lPurt)ose
vias rMp;i.rt.was prepared to summar!ze deiberations of the NuIimc SuL'ommittee'uf the Amerikan lelicopt-r Sot'it-t', pertaining to no ,ie irom low dice oadail.g air' raft.11,. :'bconmmte ttxc irtmi'td existing knoi'wh: about the aerodvyarnic sources of
nol.c and the ability to prodi.t noise, anti Alio couma'ered the ari-as wherc additional.i:,•ic: rct*:statin ia rLcquirt~d.
Noise is defined in terms of mechanisma rathe'r than subjective characteristics ofthe noise. Regarding :aeqluacy of theory, existing thc'ur!es or new analyses usingexisting knowledge could predict noise if adequate werodvnamictdata were available.Lark of awh .data is the principal shbtadt, paftkula.-l-•r tall. rotors. In "dditi'-.the report "identifies advances in teSt instrumentation that are required to pro--,;-milss-rg experimfental data. Research programs arc recommenrled to deveLk,, general-izd rotor noise th~eori-s and basic experimental aerodynamic data. Specific areasinclude dynamic surface pressure measuremebts onihe rotor blades, determination ofwake system characterisdics, and Investigation of flow field characteristics.
C.ro"arlsnn With .:imilar Papers
Thib paper Is Intended to summnarize, the state of rotor aeroacoustic knowledgeas of 1972 in general ttrms. In this regard, it differs from surveys nriente- toward
specific Investigators, such as surveys by lubhrd2a and by Mor3ey'9.
Evaluation of Pap.r-
1 The Subcommitt*'.,s fijidings apply to thte present state-of-the-art and offer Houndgeneral guidline0s fur continuing research.
47
Filotas, L. T., "Vortex Induced Helicopter Blade Loads and Noise,,' Journal of Soundand Vibration, Volume 27, Number 3, 1973, pp 387-398.
Purpose
The author seeks to model blade/vortex interactions and provide the Fouriercoefficients of airload to be used in t•h3 Lowson a..d Ollerheadý expression for rota-tional noise. The resulting method can then be used to define effects of blade/vortexinteractions on rotor impulsive noise.
Summary
A model is developed consisting of a finite aspect ratio wing and a series of Infin-itely long, parallel vortex filaments. Spacing between vortices andthe height of thewing above the vortex filaments are adjustable, as Is the angle betwee th. wing and afilament. Linearized aerodynamic theory is applied to detarmine the transient winglift response to an encounter with a single filament, an! the total respoese to a com-plete array of filaments is obtained by superposition. The response Is expressed Asharmonics of loading which are compatible with the acoustic analysis dt Lowson andOllerhead.
This model is used to calculate noise for a simple laboratory represeatnion ofblade-vortex encounters consisting of a wing mounted in a wind tubol with upstreamgenerated vortices convecting past the wing. Calculated sensitivity of the noise toaspect ratio and vortex separation Is presented. Aspect ratio is shown to have a smalleffect, while vortex separation and sp.-.ing strongly Influences far.-4eld noise. Noiseis inversely proportional to the third power of wing height and is greatest when thehorizontal spacing is about five times the height.
Comparison With Similar Papers
Other investigators (e. g., Wldnal12 2 ), have used a wing and vortex filament modelbut the present paper extends this approach to a finite aspect ratio wing and cyclicalloading rather than a single encounter. Subsequent work by Widnail extended the presentapproach and obtained good agreement between measured and calculated acousticalwaveforms for a one bladed rotor.
Evaluation of Paper
The approach appears to be effective based on preliminary results by Bausch1 5
and Widnsi12 2 . If efforts to parameterize blade-wake ez'counters are successful,impulsive rotor noise from this source should be fairly well defined.
48
* ~,e.It. N., l'.:b:.
A\ i~uzil Nalwaal~ Fi tninifl, .ri..:. in 1, Iiit.AV.'r vlv,~ I' v;rttr~ in No 0 ix: 1'74.
I1w, rt-posrt 'Ivs' t-iI.: a~:i to m:cztý.ji- icut',r noise t, d high frequernev Wu.de I adsSirnUL. azwe:uld, ~:1111Ift, v--1'1.:1 .. 9'.1:rIt' AX ia IAtvvenf izieasured and prL-(heted noise.E ffc t~z 11 t-korthiw st a. *.:' 1..3* -t1`;' * :111;1 Z onadii p i. e orref
S umrn :. r
F1.~ 1 tul r'ti*j1 1:.cu aud Lxaltul iv-.1 r',ttionalnoise. liest :i.rver.wint 1 .. .. ..... w ~~(horaw.ise, kIia, whiltele*at satisfaketorrvui: . .- *Li:war.hrie distribution.Pha:s~ingr of the ii;ia'. Irt ,. w:a: r.r-at! !' ~--w ' the CACkuuhte. level of thefundamental* noise. f:r~n In:,aiiir. It~~i nn tivt the contribut ion of.the aft.FY Tof 6t hte YI:a.ý I-, ih- 4. ti% wt .L.:0ir.4 o-'t-tficlit.r tendled t. worsenagree~riwzf Ix-tween pr.*'.z#;t% 1 fli I..:;:1"'t~ d ' 1:' 1.ejr;1.qonies. Airloads base~d uax theforwa&rd 4**0 tif uINt d~.:i I.: ti.,!u,*i*1 -.0a.h L... t!?EI* .-,;t-nfLa:ntt thdtn .airloacls tiased on theentirte Owiril. N.pi~i.v *.**--t j.f r-n hizl- 411 (riA l e:ii4ioeffwivnts tsendeil to grosslyover-estimati*te Ineit.,.lwri..i i eisl
* * ~~~Compari.son With S; ~: :a.
Cuprr'Iiati-in r ij'4ht! -'.a*..-; 'is IAx 1 c1.i::e1i w-t I iiu~jfljri tf IIIfviC?us work regardingusefulnless of voneleeW~I :i.* ..: 'io aw~iin s iu *lviI-dwise) for prl:'icvting nloise Irorna hovering rotor. lti*' rm(i11. ro*ý.ults agrevt with tother investigators that reetingrutarchordwise Ionduing is .iwt %,,,.,w%1 :ipparomirwiticon ror isse in the acoustic model.
Evadu:,tion of IP.ijw r
T'he study~ is u'ielul :i :a :t. *.( Of 'siyrk~livnzCel iiuiso andh ujeirssid daitax attire~dunder onit .ro)[hul voni. [it i -i'% 'I 1..4': 11*tlts iflusrt. r~if ltt good loadintg da.ta ~ed
91!i C.O5t eIV'lat t,:i ;i:, I1.1n..L -t V.!1 :avoustid tawl vui:ivs is used. It niav the~nlw.coneludeuI that. the 1IhJl;.&!iIA aat PIre:.entl.l is the we~akest com~poneint of rototr noise
Hubbard, H. H., Lansing, D. L., and Runyan, H. R., "A Review of Rotating BladeNoise Technology," Journal of Sound and Vibration, Volume 19, Number 3, 1971,pp 227-249.
Purpose
The authors seek to provide a general technical background related to noise fromrotating blades, and to present a bibliography of recent (post 1968) work In the field.
Summary
A brief discussion of propulsion/ventilation concepts Involving machines withrotating blades is followed by a description of aerodynamic sources of both rotationaland broadband noise. The Importance of unsteady, periodic loading is noted forrotational noise, while the need for a statistical random process approach is noted forbroadband noise. Presently, much broadband noise prediction work is based on grossphysical properties of the rotor system rather than on the underlying physical mechia-isms. Effects of ducts enclosing rotating blades are discussed qualitatively, notingchanges in source amplitude and directivity. A comprehensive bibliography is pre-sented for 1968-1971 dealing with propeller and rotor noies, compressor and fan boise,and duct acoustics.
Compzrison With Similar Papers
Conclusions and recommendations of this paper are In general agreement withother surveys of rotating blade noise technology.
Evaluation of Paper
The discussion is useful for an overview of the noise problems for rotatIng blademachinery. The bibliography and referencea represent a good cross-section of signifi-.cant information in the subject areas noted_. - - LI
'C
~ H. ~. * 1 ~ .ienE o~f a i en'u:for IWA.~rI.i'3Z. Preddofý.lo isd E;ectronic
Snhssa) Mtlricsj'.ter itutur XjisL, USAMI TehiARpr 7 .6, A. lrh1573. J
''iksi report (k~~Ut~he devetapit~ntv of a method for predicting both broaidbandand rotaiticn~a[ rm..or ilmz.a* andl f~jr siitht-sizing the acoust~c waveform for d~ae In human
Sun, tivirv
An LdIakmorate. tbu w ed.o v- pr..t-if .tili,.irn -in -r~pir.cal data base to predict, rotornuise. Cox re-latjonjis::;hown f.ar two lt-wing configurations anid one Bell canfiguration.-Predicted and nivW:asuraa i :.pa16.:1 ir i v.ut
C~nmpirisaon With Siroiirl'aj1 PNa1
The praest~nt stui~v is- amni jut. 1r h~aving- NW the niolse prediction and analog simaula-
tiOn cornbine'a. ofsrtniifý pr-6 tin P'' ccurac y ar ear to be related to Inade-quate input data, ai pri-iuih.in~ cinnnionZ to :ta1 prt.siaflt me~thods...-
The deavelopmiret o~f a mI.*thod I') PN.:k'irt the acou~stic waveform of rotorcraft is*highlv-dteirablva, baut it i., pirvinture t o a (:ept tht! subject method As a djesign tfoci.Correlation rinu:;t he -de iniAist'r~atd for multi-bIluIo-d rotors in hov'er and at hig~h for-ward speed. If %roaod ri-saalts are aulitaiitad, liaja. methud- should becomne a useful desigatool.
Leverton,, J. W., "The Noise Characteristics of a Large'Clean' flotn.r, Journal ofSound and Vibration, Volume 27, Number 3, April 1973. pp 357-376.
Purpoge
The present study seeks to measure the noise characteristics of a full-scale, two-bladed rotor installed with the thrust axis pointing down to avoid recirculation effects,and to compare meastircd results with trends given by theoretical and semi-empiricalprediction methods.
Summary
Three separate cumponent3 of rotor noise are identified: rotational (discretefrequenzyj noise, low frequency broadband noise, and high frequency brordband noise.Variations of rotor noise with thrust, tip speed, -and elevation angle are presented.Leverton's data seent to depart from rreviously accepted behavior of broadband noiseand overall sound pressure level with both thrust and tip speed. Rotaional olse Isnot treated in detail. The author hopes to develop empirical formulae for each noisecomponent in future work.
Comparison With Similar Pape !L
The present paper is one of a limited number of reports on full scale rotor noisewith potential for defining noise directionality a& well as acoustic saUvItie3 tochanges in operating parameters.
EvIluston of Paper
Results are uaeful In compat lna the three source regions, but more InvestigationIs required to establish that the presented tbavior is not influenced by the test standconfiguration. Broadness of rotational peaks and behavior of SPL with thrust andspeed suggests that the inflow might be tu'bulent rather than "clean" as the author hadhoped. If the installation Is responsibie for these acoustic characteristics, the generalapplicability of the results might be limited.
52
.1 ~~ r. N -ý Pak l:L*jrt 1: _.~ ~ .xa,1 1;:~lt
,tI Aiss u ,; 3 riJt-'r:,;t~n to define~ wh~iai. ~:`n.;vn abtout biado slap and to altt-n,:tx~ fraulaite critc.riai for ZLC ovvcurr-ni.t- Haid AIa.kp.
A re~view (A a,-.aiiahle Littvrature lexi:L Mth l1 t 1 . o tdlentily ir~turactions but-weena.~r L~:i: :ad strong tip voriivos :1:4 thal Tfliii, a unit of blade s.ip. A "Blitcle Slap,
l-wI;- i~i ý:.-Vvtlaovi whkh jpt iri to a~rrec wit.4 ma .H1:dule data for tan~demn rotorV'L.hidev_ ,ti for fi-w-WailA~ An!t rL-'tr " The intt-nft of blkde slap iioite.4 pvidicw'i. to Vary as thc s:ix~th puwvr cot fl,..: rolaitum-0a Qi oLd
('ornj;:.rj!i1 With Similar Imi.1rrI
Titis Ipalp'r Isa one oflit tk* ':riir effo r L. Ilo t~ itdy Mat.1 I- .stat) (i mpul Aive rotor noise)-. ~ ---- --- -- causucI by bltuila %vort.*-x intertetion~s. It ý:crntaia test daita from'experirnents conductedI
-a p-i, - -. Aa~ I f (b1 ;i;w _p-1 u- -:u r v F C *h:f tf ii hi rii- Fpt ýiPfr r: I r iti cu r tr a a z I h -,ql i-W Srr~'fhe*st ti~attt ouli lx- useful to othiwr invvstaj;itor~.'
jI~il~ r(!u.au in* survE:. t:g.(jn.iilAIj~ nwv!t.:uuij,fli:; Ct'spalAblki! for IJladL slapanid Iztade/vofrtex ;zteAct 11,01:4 liv (ch kt ii he a sirntifhvant eaus. Atte'mpting to atpplythe. bjlade. :iIap [a-r 1-:ritaeria lIt. hia'h :;I..1ightg cd.1 Angle. roto~r helivo-Fitu.t-i is~ notconsidert-iar to hea rc.:al i:Iie, ijoc'e:'nlr.ili ii fc~art- lik-&'iy to s )Int roll the.i in -
Pulsive.a 3u~
Le•-erton, J. W., tHelicopter Noise - Blade Slap, Part 2: Experimental Results,N'ASA CR-13H.: March 1972.
lXirpuse
°1 his report presents the experimental results of the overall study, including asubluctive evaluation of the noise and a revised "Blade Slap Factor" design criterion.
Sut. .na
It is shown that the occurrence of blade slap generally increases peak-to-peakrotor noise by 10dB. Blade slap components of noise are seen In nar'owband spectraas long as it is subjectively detectable in the original noise signal. Model testing isiouad to give data as informative and valuable as that obtained from full scale testing.L inated subjective reaction data indicates that helicopter noise withotl blade slap mustLt: approximately 6 dBA louder than helicopter noise with blade slap in order to beequally annoying. A Blade Slap Factor (BSF) criteria curve Wi presented. although re-sults may not apply to large, multi-bladed, single rotor helicopters.
Comparison With Similar Papers
T*he present report completes documentation of the study reported In Part 1,NASA CR-1221, 19C8.
Efaluation of Paper
The collection of noise data for full scale and model hardware to useful. Subjectiveie.iults are too limited to be accurate but do give a broad-brush feel for the subjectivevffects of blade slap. The applicability of the blade slap factor criterion needs to bedu nionstrated.
A- ,
5'
I~. W r *2 WW_ ýý, L'i73 61l-i2
1113IMit~;Wr :cjunp~lrus broadhand noise generated by ra-meA rotors'zin-d full-sc'ale~rtutk.:r,. ISiuth lOW fLi !jUtVflV' :ihd dih irequi:~nev ibroadbhand nois c oxnpimcnts are con-
'I ar-:iivlfl noise dat are :inal-j?.cd in~ tz~rnis (a Io%% **frequera'v broadlhand wadst. :n.:slLA-jh:ut! FWV broduimial[~ nijise. for bo0th fulI-.-!ahe and n,odeA rotor syhtemq~. ui
spi-vtrii fvr Ot!e twoi w.stvinfl: are similar, except (or O.Pctcd frequenoy Aluft:s bctwuen,.v.i tand I lll Scale. Solni.tivity (if low fritquenv'y brea-lImn'1i noise to vefc-vity ifi from
th.- .Aixtl it) tile pog~l)ttwer fnr ful~l ý:valt', ctintraste(l with the fourth to sixth powerf~jr modl " a' T*rt:~ Lehavior Is aiiffertinnt from other invetaitgators rcrorting avolucityN 'Jiluarf-d uhapCndiiete at (ronntint thinzvt Flet-pinvence of noise frequency on-idw-lty Iis fournd to vary in I StrouhtaI fitshion for inotio rotors contrastcd with no
eloar N-*Lavior f~tr iull -;ialc ro~torsi. Thinx! full-scale ruesults disagree with results
I tiigh fr-tqfut-uV brai~l.l and ii it., i!; found til fI it- 0t;rly lrindi~ptdi~iet uif thru.-t Ait c~on-~.t~nt ~ iiji t i-, r ;l4 tI~efouth ;r*-ver (if tit) -Spieed A Comnstant thrust, alth-ough t'h-e
i'i:lxiiyj.,i- I.~) 1ilron.-Av oin meIiieu reuiivi lov:lt ,io rulative Nto limit r(obir. Thev ilzeh.an-
av.n rt-iins hle fuor b Ilds)niw is not vilearly inf'Iriterntooi. Ilighi I ac' uentv brn~alhazulP-E gene ~r~illv ides- not iaunt rol Olhe overall noisc le-vel, but it can lx, a sigrific antfaictur in iuliwi-t ive i-.it ion to) Oth nol.is.
A-. ~ *.fae.ay thev aut ors. fill he uloject resu~lt; alitfe a froain ttione of previotis iua't sti -Iratirs ri-gra ruing' OW he "It' ll m %#It ' aloitv kmo noc.l so ifijiltude .,nd frelpiviuauw. Tlie pt r'setntpap'*r uisl inhiI boti mo I*I.IS andl itill :;ale data, wtilev mouiot -ither 1-:pers ame rucstricti-4l
tO ueor Ow he tlir.
'l-u' u -. 1pjimulall utuly pe rvI~l,-i .1 u.'-f'ill I cx fill ~iifiler *~:rh nlafol:.v"f.* eur~ffizalý iio'eh1:11IIIi :!' wil: !bp~~i il .pi ifriiin ,0w-i o n
t11ll siuahi Iug-Iot-'a'ur.. 11-i.'1 I u.'sua I ~ miy'tol 14athe A141.tulae SAouhi,'it lie rvictA toI1*
III-6.1-11111t.~~~~~~~~ ~ ~ ~ ~~~~ 114 IiA111'11milmtit: lm ilfl- i i-e-1
Loew•v R. G., and Sutton, L. It., "A Theory for Predicting the Rotational Noise ofLifting Rotors in Forward Flight, Including A Compariaon With Experiment,"Journal of Sound and Vibration, Volume 4, Number 3, 1966. pp 305-344.
Purpose
This work attempts to provide a method for predicting rotor noise from unsteadyairloads. Noise calculations using the developed analysis are compared to availabler! easurements.
Summary
Expressions are developed relating the noise field to oscillating pressures Imposedon the air by rotor blades. A swept area representation is used in conjunction withspecified chordwlse loading distributions. Limited comparisons of measured and calcu-lated noise show poor correlation.
Comparison With Similar Papers
This study is one of several that demonstrated the importance of unsteady loadingin the rotor noise problem. The prediction method Involves a numerical Integrationand therefore is slow and cumbersome to use, as are other methids using this approach.The correlation between predicted and measured noise is somewhat worse than resultspresented by other investigators.
Evaluation of Paper
The technical approach and final prediction method are similar to those of otherpeople studying rotor noise in the same time frame. The relatively poor agreementbetween predicted and measured noise is probably a result of inadequate blade loadingdata and questionable noise data rather than severe defects in the analysis.
56
r " q:;(11 M. cV. cnd O'lerhead- J.'B., f!ehcn;oter Rotor Noi.e," USAAVLA-i
Tit t.6-,O, January Vitb,).
Pairrnose
Objectives of the reported study are to analyze the problem of helicopter rotornoise radiation and to develop analytical expressions for .calculating noise from rotors.Existing theoretical and experimental information are the starting point for the study.
Su.mr'.mary
Discrete and broadband contributions to total rotor noise are described, and theimportance of discrete frequency noise out to several hundred hertz is noted. Experi-mcnt',I data are reviewed and general trends with tip speed and thrust are noted.Analytical expressions are derived for a simplified closed-form acoustic solution andan "exact" solution requiring numerical Integration. The simplified solutlonis nearly asaccurate and much faster (I. e., requiring much less computer time) than the exactsolution. Design charts are presented for estimating levels of iotational noise har-monics as functions of equivalent Mach number and elevation augle from the rotor disc
Comn.rison Wlth Similar Papers
This study is one of several conducted during the mid-to-late 1960's concerninghelicopter rotor noise. It agrees with the others regarding the Importance of unsteadyloading. The priasent study is unique in the development of charts for estimating rotorrotational noise.
Evaluation of I'aper
This report is very useful, both for a technical overview of the noise problem andfor the simplified predictlun method It contains. The concepts of airload exponentialdccay laws, random, phaslng.-and spanwise correlation lengths have become wellaccepted since they produce reasonably gdod noise predictions from manageble inputdata. Banic shortcomings of the method are its Inability to simulate acoustic radiationfrom highly unsiymmetrical toadlng on a rotor, and its Inability to model the effects of.iubtle chanrges In "iIrfolls, planforms, etc. Much more basic research is required todievelop) the a•rodynamiIc data base and aeroacoustlc transfer function In order to remove
preRdictlio Ilu iltations. The subject approach and t, implliled metiho will remain popular,at htnast utill !he ne:c .:.a ry reatnarch Is done.
57
Lowson, M. V. , Whatmore, A. R. , and Whitfield, C. E. , "Source Mechanisms for
Rotor Noise Radiation," NASA CR-2077, August 1973.
Puroose
The work was performed to investigate sources of subsonic rotor noise. Varioustheories are reviewed for discrete frequency noise and broadband noise. Theory andpast experiments are compared, and results of present tests of a low speed fan arediscussed.
Summary
Fundamental theories rel-t1g to noise from turbulence and unsteady coherentloading are discussed to lead into a comparison between theory and experiment. Parti-cular emphasis is placed on velocity dependence and frequency dependence for dipoleand quadrupole source models. Theoretically, broadband dipole noise will tend to varyas thd sixth power of velocity while quadrupole noise should vary as the eight power ofvelocity. Existing dlkta, including that produced by the subject work. do aot resolvethe dipole versus quadrupole question.
Major conclusions are that discrete- frequency noise results from Inflow distortionand large scale inflow turbulence, low frequency broadband noise results from smallerscale Inflow turbulence, and high frequency broadband noise results from a mlf-inter-action at the blade tips. This last source of noise is not Identified I& past liratAre,aceording to the authors.
Comparison With Similar Papers
This study is compatible with other literature on aerodynamic sources of noise.It Is somewhat unique in having hot wire anemometer data (rotating and fixed probes)to define the input flow field that produces the noise data.
Evaluation of Paper " -
This paper Is useful in establishing firm theoretical and experimentsl foundattonsfor basic noise generation studies. Promising results for the discrete frequencyaeroacoustic transfer function and for broadband noise correlation help direct futurework. The quadrupole vs dipola question needs further Investigation.
38
°.2 ::1, it.,: 1L., M a i' ; , -W .1) .1 .. .L •. "r, % t. . ........ of !iH =•:rR t r"i~
, -, ;" Not -iv." J::urnai uf tl.-t Acouutlcal Scci'ty of Arercic, Voixne 53, Ncimbher-. -j,:,, pp.0 -•l•
In order to reduce noise at lugh forward speed, the author seek to develop a caltu-".IXIUn (.thod f-r generalized airfoil ,hiclkness and lift distributions that are predicted
i,) 6, .-.ss noisy at Mach numbers approaching 1. 0.
"The present work extends earlier efforts by the authors to relate noise from thetip region of helicopter rotor blades to blade thickness and blade lift. The contribu-tiox o" lift to noise is shown to be much l.ess than the contribution of thickness, soL.: ,:,j.h-i is plavced un rnirmizling thickness noise radiaion. Some candidates for lownolse tip distributions are presented.
Cum•parison With Similar Papers
'Fhe Stubject paper is more abstract than most, since it devclop;s generallzud thick-ne-,s and lift functions that can be satisfied mathematically by many different designs.Oth-.r papers tend to concentrate on reducing comp-essle drag cf specific airfoils bychrn.ir.g ,:wcp. thi..kncss, and angle of attack.
F .ld.•ton off Paplr
"The, results ippvar to v•- Valid In a i;athcmatical sense, but the practical validityo; the :ipproa,:h must A- :;.:'mnistrated by t%&! design and test of airfoils based on thismnethod.
Morfev, C. L., "Rotating Blades and Aerodynamic Sound," Journal of Sound and
Vibration, Volume 28, Number 3, 1973. pp 587-617.
Purpose
This paper is written to provide a survey of fundamentals of aerodynamic noisegeneration by blades.
Summary
The author traces the historical evolution of current understanding of the noisegeneration processes involved with rotating airfoils. Early work on propellers ismentioned and advances Into unsteady aerodynamics and cascade theory are noted.Noise generation and radiation from rotors in a free field Is emphasized along withthe effects of ducts on the acousti- field of fans and impellers. References and inextensive bibliography are presented.
Comparison With Similar Papers
Historical development is traced somewhat more extensively than other papers.Results of specific investigators are discussed in addition to gensralizations regardingnoise generation and propagation.
Evaluation of Paper
This paper contains a useful overview of acoustic technology for rotors and fans,and useful bibliographic data for more detailed study In specific areas.
60
-. ,rS. ., , .n, .K. , a.nd Evans T, ). j, "'•rai natton of the Aeroiw;ainargic'"..c .. :x f 'o-x,,' . ,,Sh ,,. From L:ttinr Airfoils for A.pticuirion to th.i Analv-
--A lit...corr Nji:-."' n. •tr A!eplid Scence Assoclates, [ne. , IRASA Report
'l!.k p:r'..ent stud, '.':ih Undrtaken to e:,:..rinw.-ntafty define the characteristics of
vort.x shedding from ailrfoils in a. wind tunnel as a foundation for understanding wnd
preeficting vor!iwx noi.-ce of helicopter rotors.
* :ummarV
A;rfoils were tvsted in the rnited Aircraft lIc:search Laboratory acoustic research
turflei to gather blade surface pressure data and corresponding noise data. Surface
pressures were adversely affected by the transducers on the airfoil. Presumably,
noise data also suffered. from this effect. Two values of Strouhal number were found,
but reLpeatability of results was found to be poor.
Conurarison With Similar Papers
Present ruesults do not comip:re well with other Investigations.
Ev-Iuation of Paper
11ennistcneies in the t.est data m-'"o it difficult to apply the results of the study
to helicopter noise.
61
Schlegel, R.G. , and Bausch, W. E., IlHellcopter Rotor Rotational Noise Prediction
andi Correlation", USAAVLABS Technical Report 70-1A. November 1970.
Purpose
The program objectives were to measure airloads and noise simultaneously andto use these data to evaluate correlation between measured and predicted noise.
Summary
The rotational noise prediction method reported in 1966 by Schlegel, et a16 Isextendied to use higher frequency airloads and to use any arbitrary chordwise dlstribu-tion of airload. Good correlation is claimed for the first 4 harmonics of noise. Cor-relition generally Improves when the measured chordwlse loading distribution Is usediastead of a hypothetical rectangular distribution. Source motion terms appear to beimportant and should be included In the prediction method.
Comparison With Similar Papers
Results of the subject work generally agree with other reports In that high frequencyairloads and chordwise distribution were found to influencenoisesigniftcantly. This re-port summarizes high frequency differential pressure data mes,-ired on the rotor blades.Such data generally is not available elsewhere, especially for a tiight vehicle operatingat high forward speed.
Evaluation of Paper
Although the modified noise prediction method produces better correlation than theoriginal method, the need for high frequency airload data to calculate noise makes themethod difficult to use. This is a common problem with all existing methods that pre-dict noise by integrating over the rotor disc. Since the needed loading data rarely isavailable, the added complexity does not generally result In more accurate p.e•dictiona- -than closed-form methods have demonstrated. The aliload data could be useful infuture etudies.
62.
* :..I.L&It. dr.:.i~.l, i F hta, . ,a~d~ rR. ,"Aii1:("a.fN.;a C1u-r.P "act a .,r,. U.So. A Pac't Anv C ._earch
- i)urham Riepnnrt D2IO-10550-1, Novebrner 1972.
"ihs p:iper prosviLn results of a study to develop an improved version of Lowsonand Ollirlcal's novise prediction procedure called IERON I1. Experiment, analysis,
and correlation art! presented.
] S'.-; nn.:. m ry
A noi:..; prediction computer program that predicts the acoustic pressure timehi-.tory, from which noise harmonics are extracted by Fourier analysis, is duvelnped."iTh,.s Lasic computer prograni requires detailed input data to descriWe spanwise anti
chordwisv loading djsi.tribution as well as azimuthal loa|ding dietribution. Hypotheticalmiputs were ushI and sbh)wed insensitivity of noise to spanwise'distribution. Amplitude
aad phase of loading harmonics were found toaffect noise significantly. Based on thesensitivity study, simplifications were made to the noise prediction program to remove
ut, need for- c(nnrplicar-d- inpAt data.- -Simpiifying-assampti-is -of L6wsoni and O6ferhea~dare validatud.
C,,mparisi;n of mudel and full scale rotor noise harmonic spectra shows excellentagreement one diam,-ter from the rotor hub. Scale. factors believed to bxe critical arethrust coefficient divided by solidity, C r /6, and tip Mac:h aumber, Mt. Broadbandno:,iise u.io:e. not scale as well, with model level. being lower than full scale.
Ei:periznental investigation of acoustic sensitivity to airfoil sectlon and planform
,,huwed no clear cut improvements over the total tip speed-thrust ranges considered.Some noise reductions were noted at lower tip speeds (650 ft/aec).
Impulsive hover noise of an Isolated rotor is thought to be produced by shockformation (-r movi-nvrit on One uppe•r surface above ift -- lvergetic•.: These shooks arc:attrihutcd to th, passage of a tip vortex close by the b.•de in question. Blade loadingand tip spei are belihved to bx- Ihm: Important parameters than the airfoil section liftdiwV,:rg.'ii0; boandiary. Ability to predict the occurrence, and amplitude of this noise is
lifiitfd by a lack uf ad,.pluate information on vortex core size, strength, and locationrelative to the blade.
Co•.-rjr-'rinon WI1h Yimiilar '1p1:1rf.I'
The Mkalylical approach paralhlels that of I..wson and Ollerhead7 .• The present
p:aper choks many 4f the si rnplIfving amsumpt ions used by lowmon and Ohlerhr~ad todicv,:l-o th,!ir A;mplifi.-d, vlosed-form noise prediction mi.thod. Tl'hso ansunmptlons
63
Comparison With Similar Papers ('ont)
are found to be valid, and the number of IoadLng harmonics is found to be less thin themb (1 t )0 specified by Lowson and Ollerhead. Experimental data for similar rotorswith from 3 to 5 blades are presented, but no attempt at comparison with other studiesis made.
Evaluation of Paper
The paper contains reassuring validation of the simplifying assumptions of Lowsoaand Ollerhead, and some additional simplification are presented. Test data containedin this report might be useful when comi*dned with data from Leverton and Lowson for
noise mechanism research and verification. f he role of oscillating shocks In single
rotor noise deserves further investigation.
64
A. V.____ _________ NtV.Son Efet of Ground and Side Planes on,
P -L.4 I,.t .iJ to, NASiA CR-13'230;R IM"
m, :iuthor.1 nL'ek Lw SM~ULat the effacts of rotor/airframe interactiona on radiatednu1,t- 10 ie its ol a si.Jnpil eywdel.
i,-sa ically, sid4eplaneis irerase lower ardor rotational harmonics significantly forjutlie- j'rropvil.r -,'op~ai~aton5 lese than~ 0. 25 prop~cler diameters. Grou~nd Flanes
Vvtrv -,:10:-w to the rotror cain devr'Žase rotational at'ise lad Increase thrust cutpat
*iiw subjtvi t pa.per Is uaiiiue in deaaling -with side planes- and ground pianes represent-in,-, f-:;elajg,: structure. Other papu'rs dleal ýýpcvlif~ally with guide Vanes and slipport...trut, clcountercd in (omp;'ssors and ducted fans.
rhL acoustic effects of the side plane-rotor tip separatic.; .Ire useful for designoft turboprop, jpr(.p-fari, prop-rotor, and propeliler instalilitiouai. The eff4 :et of tileground plane i~l not bv.ileveci to be applicable to rotor-fuselage Interactions for largedilamneter rotors.
W_ a.l, .•. E.. •"A Correlation of Vortex Nise From Helicopter Rotors", Journal of
Aircraft, Volume 6, Number 3, May-June 1969. pp 279-281.
purposc
The work waa dune to see if a genoral collapse of noise data coald be obtained
on operating condition and geometry of lifferent rutors.
Summary
Data from several references, including whirl tower and flight vehicles, collapsedto a band approximately 5 dB wide. The collapsed data show a general trend with the
mean blade lilt coefficient squared (CL 2 ) aear typical design point and devilUon fromL2 for both highly loaded and lighty loaded rotors.
Comparison With Similar Papers
This paper takes data from several other reports. Parameters for the collapse,such as thrust, tip speed, and CL, are those commonly applied for so-c.alld "vortexnoise".
Evaluation of Paper
The data presented in the subject papet are ,iscful for a "first pass" estimate ithe overall level of "vortex noise", with quotation marks indIcatLng that this Is thepopular name given to noise above 150 Hz by researchers through the mid to law1960's. The data also are useful as a reference for measuring bi much nois re-duction is obtained with new noise control rotor systems.
66
~* r ,riiov vf.re'hi-iop for :,o!2e fromi Wadth-vorte~x
indAuc~L. '~v ftl ill~t~ w,-L~~gO1 I foll fdIJ *''I A -( U ild Coin-pairison f r.. :-~~,U~~~v£2~ (.,wtI~ ;jj~ -blic.4d rotor w.Nith pr dictc .1 wvi~.-w~frms qh(,wtd gn,:sti alf t
mrnift.
This~ ;ipatr is wij vf several d!ealing with rotfur noiS,, -d~u( to blade, vortex inte'r-J~1 ;.t:~.1!Li mcp',. r.:%ttn L v-\tf'~~ ah'nimi xa;t, houw.ver, -;Inco~ fprediict.d .-iunI poer
so-U1.id ilr(.Ptivit.- , a&nd :ioIund aqwŽccruiU ;&r. prv,~srawel, Also, theŽ comuparison with-TP.1 1:1.~1,1 IL-1ui' lddi!ionali crfPdil'Ality to the *!- al~ ~ts4.
Ev~eallstiun '). L
flWit.I su iot p qw.r Jprt'-.4fl a~. fairly cornplit! oiaI~ s~f Ihadv.-v )rtt-x ifatc~raciml j.
It .,houla~ Ie~p 1w 11:11G -1diii.Vr I£k I :1.4 sa rt~illr p(Illit. rctin whiri hto tXplurv .'ffc,-t:-. c
umif-ad' OnMIAicalmi~-L,#if adcvortx ii-r
Wright, S. E., "Spectral Trends in Rotor Noise Generation", AIAA Paper No.
73-1033, Presented at AlAA Aero-Acouutics Conference, October 1973.
Purpose
This paper was written to report trends observed la studies of measured noisefrom fans, propellers, and rotors.
Summary
The author's analysis indicates that the "mdnimum" moise megerasted by a rotorshould depend only on thrust and rotor "self n•ise". The euor foek that only thieminimum noise is readily predictable, since so-called "exests nWs" Is oascedby so many environmental variables. Strouhal ecaling of bresasead frequmecy isobserved, and a data collapse to presented. Time depeadme wof pmrated mss Lsnoted to be on the fifth power of the velocity.
Comparison With Similar Paper.
"Wright's results should be checked for comoatibility with rsold imk by Laveukoalland Lowson 14 regarding noise mochanlems and rotor sooustic bshauier. Be* ftaqeydependence and velocity depeadewe are Ia dispute anong tuvstigetsrs.
Evaluation of Paper
The results presented in this paper are useful a" a base for fordw uea INnoise from fans and rotors. In particular, the data sbould be ussemi Ia trying to deftieffects of velocity on noise amplitude and freq•as•y.
66
- . 1.. .. .2 r5ultttll for. :s on ro2tor
t I.
4rituts,,, v~m-
ii 1% t -,. .1. t''
Iii ~ ~ ~ ~ ~ t rot~ .:.b.. . d~ at ional aoimt gt'ncrat Ion of
.44
is'' "t.eCr :e Sizimartes
Eatoc ti. fJ. 1 ;,I .- : . 0 1 ';airt.b'ir-, J. A., "Designing Small Cas TurbineEngines for Low . ':.Nn-;-- !ea!, EN'aaut" AIAA Paper No. 73-1154 Presented atthe CASI/AIAA Acivr.4utic. Nieetirtg, October. 1973.
Purp3.se
This report outlines wc.rk being, done at Pratt & Whitney Aircraft of Canada,Limited on the control of noi.ze awn unmissiorns of small gas t.rhriLe engines to meetFAA :.nd EPA regulatioas. Design features contributing to tne low noise signaturesof current J''1i5l and PTi ,-ngines a'c discussed together with some early resultsfrom programs to minimize nise from advantcwe PTI; turboprop installations.
Summa ry
Although the P*I i. cngir.c was Iesigned before many of the engine noise generatingmechanisms were fully un,'cratood, it does incorpor.-te advantageous noise reductionfeatu.res. The free turbine elixninatLs the clutch requirements for helicopters andallows for selecting speed for minimum noise. Moreover, the gas path configurationis diff':rent from the conveo'ion-l s ngine. This generally results in a buried engineinlet with a multi!%icity of riglt angle bends which effectively impede noise trans-mission. An example is shown which illustrates the effectiveness and importance ofinstallation ducting on inlet noise.
The measured exhaust noise spectrum of the I'T6 in octave bands is relativelyflat, with appreciable low frequency noise. This noise is internaily generated andbelieved to result frots the interaction of turbine flow turbulence with the exhaustduct. No attempt is made to separate combustion noise from overall noise. Over abroad range of powers and power turbine speeds, the noise output correlates with aV6 relationship where V is the velocity at entry to the exhaust ducts. However,different exhaust ducts produce noise differences of 4 to 5 dB.
A broad correlation of exhaust noise from different shaft engines. suggest thatengine noise levels vary proportionately with shaft horsepower (SllH). individualehgine power/noise variations are less consistent as the PT6 follows a (SHP) 4 whileother free turbine engines vary from (Slip)I. 7 to (SLIP) 5 .3 .
Pratt & Whitney Aircraft of Canada, Limited Is engaged in further work on engineinternally weneratid exhaust noise including the effect of exhaust duct geometry on theoverall generation and railation.
Comp,.r1son With Similar I'apern
Thii report Im of much n:,re !himiod scop, than the reports resulting from theAir Force sponsored Turfoshaft engine study at Ailleaterch 5 . Also, the DOTsponsored program at (;.a-,ral Electric" 3 dhscrlbes a more In-depth study of noise
generation mechanisms than found in this report.
71
is zi iinuited iiL.U~stc a of Ugw noiii of small ma.b.t~d ~;~~g•
r ii:.~. ::;--iotnt t-rfecns of it.Iaonare clerricretratad, jicibeit~~ ~w it's*t.( ;d- zicrn~iation rupov,, ;d. Chi is 11--.--t- cf
C ~ ~ti1 ct-nis-uti ucwift;AA v 4tLer .i~in ioin;ýe corktral or predcutlbio.
72
Grande, E., "-Core n. Noise", AIAA Paper No. 73-1026, October 1973.
Purpose
This paper a-;.,w.sss sources of core noise! i. a turbofan engines. It is concludedthat combustion e i:-; the dominant contributor to core noise, although turbine noisedue to is.teraction wiO h combustor-gernerated turbulence may be aignificant. A corenoise prediction prncx-,dure is formulated which considers the noise generation in the•combustion chamber and the noise transmission through tne turbine ,tnd the primaryexhaust nozzle. ('otnp.ar=.on of the predicted and measured core noise leve!s for onelow bypass ratio mnd one high bypass ratio turb,,fan engine shows satisfactory agree-ment. TM! wo'k on pA':diction method& of core engin.. noise, though not dlrec*edtoward turboshaft erngines, i.i ot interest in hlidcopwt ;oIse prediction and will yediscussed below.
summary
Core noise coroslsts of numerous and only partly identified sources of noise in-cluding:
1. Combustion noise
2. Low frequer.cy noise generated in the turbine as a result of Interaction withupstream turbulence for the combustor
3. No•se generatwd in flow passage discontinuities such as turbine exit struts
.1. Turbuhenve level and swi I in mean flow upstream of the nozzle exit
Combustor noise has been assumed to corstitute the major source of core noisein two separate prediction procedures by Gerend, et &08 and He and Tedrick4 . Gerend,et al express the core noise as {auctions of combustor exit temperature, turbine Inletarea, and turline pressure ratio. Ito-and Tedrick express combustor noises as func-tions of temperature rise, combustor flow, and fuel air ratio. These prediction pro-cedures suggest that noise generation Is dependent on the coinbustion parameters up-stream of the turbine islet.
The remainder of this paper Is imited to considering combustion noise as a
source of core nol)is.. 'I hr'e (pseparate problems are considered in attempting to pre-dict the core noise resulting from combustion. These are:
i. Noise generation in combustor
2. Nulso transmission through turbine
3. Noito transmlsslon through primary engine tailpipe
73
IT~ *ftL. -J the %"xtaust nuizzl int nuisvlO tr:,n:.nisaqion is aproximm~ieiy rnodeledthu radci'nL fL :.tn tllei open~z itŽd ut a uniiorrm circukir pipe. ai~ing
*r~t :.!.L i!Iii3i.iUfl"t'IMolza it i .- dbA)'.f tha1t Iwfri.quýzncy noiste t;ians.misioa* .. e vh.%iL Ziu.t nzI. varirhs ifiver,.ely with naizzle tem;"ý(rature.
~ iuf r~ovnerati-.r. is cixaxrniicd iy =-AldJcatimbf of the theooreti.zal model'A r-.t L.% L t~ rnditi:i~Lc with ictiaciial rt:.sults (A tuo iJ rodrl~k4 . It 1,j
* .,.r. ; nnpirira. s l:or ,ru_-;A!!%on ~aFrias WulY with thu. modified theoretica: modelfor~ :~ of th'Ž, x.U root uf the conrLus*t'r tenr~rwrature.
I A1. priwl-diig analytaicai L~~pe t~he noise of two large turtbof:Lns wlthf~ni~, ~raitlos are, preýJ.wtcd and cuinpa&red with rnt eýuretd acoustic data. The
*t~~:~tb r.('~.i r &t.- predi tted jet nmi c, appt-ar to ag;ree with tho- coreraoi-t pr, t.hrtiun to witl~tn r I till. fiowevcr, the ea~ioe parameteri used are based on
+1l ifi. -d pti-rforrnance ev-aluuIatio.i~ for the two cngines, aind inay be somewhat inaccu-rate. F ~rthrrniore, similar comparisuns with other egi~nes are necessary to assesstbe %yAii .1!y Of the-predietior. n.,;Ahod.--
(~~rr..oriWith S~imilar Papi-r-
TI), anrialv;is and liri-eicticin scht.nic ch.scribted extend thit empirival work of Ho andk.1virick Ifrorn burner conihoustor njoise to the core engine noise af full scale turbofan
e~igI.I*4.I lhe v.Atc-i~iOii of Ov.- th.eoretIc~al work id Siruhli,'1- to pvrrmit comparison arddscedt-ii to the! burner prediction method of fit, andl Tedrick, but the extension to the
.illi.d v ~ citzilitstiir flot:v- 1 rt-,rij tioni flhlhoil was. not oxamlned. Tlhe resultingprifili v on method) of Iaa I' t' mi~rr(*kb in part with the prediction method of lto andTlarlrit-1 for burnui~ rigs, but not ior engine core noise. rhe derived predictonni-hx for tran~smission ('otfficivntts through thu turbine and exhaust nozzle have
niot bee. exainineil by other inves4tigrators.
I'vahiuatf-in of !ipeV1
ribe prediction methods fit thin. ri-port have not been mufficiently validated to he')f rnuz:~h ti),' inI pri-iltlng rorv1 enghine noise uf helicopter.
74
G;rande, E., "Exhaust Nol:,' Fied Generated in the JT8D Core Engine - Noise Floor
Presented bin the Intkrr.-l Noise Sources", J. of the Acoustical Society America,
Vo!une 55, No. 1, ,Iaruar' 1574.
Purpose
This paper presc nts the results of an experimental/analytical study to determinethe strength of the acoustic radiation generated in the combustion and turbine stagesof a JTl'D core eng:nr and transmitted through the primary jet exhaust duct. Resultsshow that ititernally generated noise is a sigrificant component ot core engine noise.
The work is of interest in helicopter noise studies because turboshaft engines may
also exhibit appreciable noise from these sources.
Summary
The acoustic field within an extension of the core engine tallpipe of the JT8Dengine was measured by an array of microphones flush rn'unted on the duct walls. Atheoretical analysis was made to develop a mathematical description of the sound fieldw:thin the engine to permit interpretation of the cross-power spectral densities of themicrophone signals and to d-ternine the amplitudes of the propagating modes. Goodagreement was determined between the measured and theoretically determined cross-power spectral density. The transmitted power was determined and far-field sound
pressure levels were calculated using directivity patterns from model scale jet mea-surements in which the dominant noise field was generated In a plenum upstream ofthe jet nozzle.
The results show that internally generated noise is a dominant noise componentfrom the core engine at large angles from the jet axis for low engine power settings.This suggests that in turboshaft engines, with their high work extraction in the turbinestages and low core engine jet velocities, the intarnally generated noise is a signifi-cant nolee source.
Comparison With Similar Papers -
This paper shows that observed levels of "core engine noise" measured in thefar-fieid of turbolfan vngine can be accounted for by measurements of the acousticfield within the core engine tallpipe. This study adds additional validity to previous
work which has suggested that internally generated noise upstream of the exhaustnozzle is a source of :iignificant noise. No attempt has been made here to determinethe source of Internal noi.4 nor to relate the noise generated to other engine operatingparameters.
Evaluation of Puper
No prediction methods, trends, or relation to other operating parameters are
available In this report. Thus the report is of limited'interest for direct application
to turboshaft angine noise prediction.
75
T~~TT7Ci7?7T72.7rT.Z 7 iTli. .z Lai~ ory Tvc::ia ~r
ia~ ~ix I~a~&cpor *,unz :rizes the work conducted under contract F33b15-j~ u.~c ntho A~iR.-.;t'rkch M~Ni. -turing Comnpany of Arizona and the Air
\,'. -P01 .. ~LabW LA;U tulr- . Th~Objective of-tlýL: work was the LjCrelpmenCtL~tv . 1", L.< o *dvUc1 t fl.,: j noi.;i: S tureýa vf sur"1l1 turtioprop
:,i. ýrbot~xa t-firiCZ to ufilfl jlrnL5 their dletectability in low altituoct reconnaissance!
.. ....I ivri~is.i~as. I L, pro-,rani suznm.inri.,vd included 1) ilrvelop-ireflt
~~~~~~~~~l it fl b'iiteS cs of ~n~tur~oprcp (turhoshaft) and turbofan* 2) '' ~anentOf .a IAIUCL :1 t U.ý:tic treatrfl:nt du ,a~lrtai jtsso a.i.t.aes, ..wOU:,tC dC sii.1ct heS. -it a:,justic ttests of an unsuppressed turbofaif
'\J.; .aAsn al ill in*~jtd.--c-tra, 51 accoustue t(-sts of* various inlet mutfflers
-a I .xh:;.UA iuct trca tiaxruat and i:) an analysis of the performance and weight panalitesfor noise .'upp rt-s s Ion.
:.1fi .at4rv oi Exer-utivae SuninmtryV.-(ume I
"' his voluniev 'iumrn:az izt..- the technical objectives and desired end products of theprjgr'riim. it.*",utts of the tlsrv' ti.-it phases9 of the program and conclusions from theu.Aerall ;~afaire imc'iudc~i. (;f inte-res-t is the overview of the program providedin fig.-ire 1 j~ 2) of thiis %'.lurne. Hore it is shown that the work in the program a
-1`4k ii lato thit'- awor I :itegorivs, 11 (it- cloimninnt of noise prediction techniques,
21dt.vchyiO,gi I- !tlstivce Jioi:ie suporhssiofl tuchniu~~es including assochiite performance:,nd. wcirh11t dtin.zite Mnd 3) coi'hal dI 'i;f irat* tv-st:i to (iurnonm:istcat (orrelat~ion with
usti~ia of s1;J)prv -Siaon tetehij-uea~s developod in the other phastes (if the progr3m.
Vor u-inagae nloise pr~effiktitn, Owe -nglne noise sources are divided Into three mainarvas:. inalte t,'sI:e, *:xliau:t ajuise and niechanical noi.4c. Inlet noise is ithat produced1)1.1 O-W fat1 .ondirfz IjPl!1 r~ad!j-d-tz'i br hit-anv-ifd and rvarward -from tOW front of
- t,..k:r, I i t~ ; noij:,i. 'iptv rtnn cmi,, a .t suf Ii~iv:'reet trequene les- at thv f-111 :and com-
pi v:i~wr 1-dvl'i a,.iAnag I reitlit:ikvy andI hartnunit-4 along withi broadhand noise. Yan and.*uniprcvss-or nose' :are preslirtesi by ;in iamiprove'd version of the mnethodl develope~d by:Saa. aiatlh in 11'.ii.wt ". Th.' lilsri)IAe4 '& p~iajresented Itin this report Allowsq predictionlofl If( hit'i :a.4s - :-nt rifuga:. ccsnipri-ssors in addition to the axial compre.ssors treated
E t.0;' l.;i1i n:.if.u ron'.:lit of pkt. ;ao:i- :;;)I! sssre nolse. Jet 11-Afao' s proshu t'l by theprimarya r,.I'/.o.iiA r" :1 ii av i ig. 0t1 he1ifrae ;arad ainixing , wilth Olhe:11bIent arCo z'a (IAisid 1.4 pr id.e'd within t~p vniirwg ateasd t-spels via thie pr~limary texhtutuat n~ozzleJ.
Summary ,f .,cit Su.,oa= r--.A .-lure I (. ont)
S• . pocedur12.Jet noise i. ps . . .... a n-tln, . Lased o.n the standard SAE procedure Corenoise is ,.F:suno,-d 11 rcI:.,rt ti be comul;ie, noise. liowvever, it is pointed outthat furthwr e:.,st .,. A tht, (c rt s. prediit tion methodoloy will result from theDYr,/FAA sponsur:. cjogr:.,1 1o4G a ted by (,eneral Electrict3- Combustion noise isbelieved to be one ,f .+,. most sig.iil':ar,. or. tctigine noise eources in small turboshaftengines.
Mechanic.al nois. -onsj:t:!- of gcar noise, auxiliary equipment noise, and casingnoise. In turbosaf: . gc.'ir r. n.r mnuat ,1e considered, as gearboxes are usedto drive the pr!'pelhe,, rotcr 0r ;jaxiliary Lu, iiprtat. Auxiliary equipment noise isthat produced byv fu'. 'tni luiud'.(liUo p)u1J1)s )ni,.ArAE id on the outer case of tCe engine.Casing noise is due '-. flu.tuat;iug Ir.. pr(ouced in the engine, either from aero-dynamic or m,.chic'i! c'auscs which are transmitted through tWe engine casing andresult in extorr.:na tl :- rrdi'ition.
Gear noi•e is r-Aittitt,! l-.th an e.wpiki al i1 coedure, since little basic work hasbeen done to atlow lri di.:;ons ironi ba•sic noise generating mechanisms. The spectrumof gear noise i. donulnated by 4is, reet frequency peaks. For spur gear systems, thedominant frequency t'..por crat corresponds to the tooth meshing frequency or itssecond harmonic. The wide variation in gear systems makes an accurate predictionprocedure impossible to devvlop at this time. Therefore, the report recommends useof measured spectrur.: shapes for gearboxes of similar geometry to the one of interest.Then the empirical -,-(.zcdures can be used to extrapolate the spectrum to the desiredconfiguration.
Little information on auxiliary equipment noise was found In this study. An orderof magnitude prediction procedure is included based on a fuel Injection pump prediction
procedure. The casinrg noise predlztion procedure was developed from generalizationof Aillesearch arnl Boeing measurements and is considered to he a function only ofmechanical horsepower generated by the engine.
The procedures discussed above are Included in a computer program. Of Interestis the correlation bet~cen measured and predi ted turboshaft engine noise shown infigures L0, l1, and 12 of this report. Overall ,hireetivity In figure 10 is seen to begenerally goxd ,,xc',pt in the att quadrant from HO' to 1i5'. where predicted levels areas much as (AriB high. Fig'ure 11 shows quite good correlatlonbetween measured andpredicted Itilct r Thes•. 'h-re do(..,. howv,,r, ap)pear to lhtonos in the measured spec-trum at 1O00 and .100) 11z which are not prmdicted by the method. Figure 12 shows theexhaust noise ,omparlson. Here, th, lack of agreement at mid frequencies aroundbOO liz 1is 1trubing. 'I he lack of similarity in the measured and predicted spectrumshape suggests that further work is required in predicting turboshaft engine exhaustnoise.
77
j' pU. .*;:;! i*cs d:. r .di. j in th-e. rcptýrt a~ an awyticai/wni. h i.tt miL lku .i;-41n~urn liner imr.pediaace for soun~d
* . ** . ~:i :% t- ;i!:' . .'Scr Id which nnatchi,,g Chis ri2,ovirmd
* .. .~i ~.u.. .: z;,ian :mtpiri i(.±i .,rocivar bad on ;, neralization o
r '.;~:t~~tr in thet. J;ct Iiiwr d1edrn area. Curn-
I ~.-s~LI .t. *.t-; %vre L~li1.iJ'cLd With and! wifthout ý-a usprr i(.n to Show M1e
Ar!;L;.:11tjXI a I&jt."V(l ;J 9 ,1 .A ~ ~ lI is :-;unanartzvd. -A1io "Ile
*~ ...:;3-,UI.: ;1 fo.r aveii'iifl. ::Uiumarizje.d. A fcw .: -.antlphlk are.4 lk ~.. .'& tho apt ~i. a n.h hev~ i&;rite4d xt aL
... ... i~ ~the ):I st.. ud.i. m~.:'esarv%. to~ doveIop tI-. e~ag~ine~..c *~i I ~fipro(. !-:iuiý w,,I; h w..: i;ý ;,ssd uixweV in the Vrslum. e I siummrary.
at OW * tnot~ in ungizae floi~ gcnwratlon are
iii :' it I.- a 1u i. '1 :1 f i-: i:n A i Re -e;i rvh 4 ngi ne tv!3t0 hil evahilittd asU, .I'jii. :wv'i ruat p r(ciicti. ;flfi iit-tiI),1 .I. Soev*ral comIparl~sans b ~t'wccn'
* .' ~ S ~ I. It. I !!rf-vti-itt'Je- :%ni ..;.i tr r;i ~f Iur~AA~fii nnd turixIO±IikjI t.nglnes
Th 4r.1'I0irld fromn tt 1,ivr ii'r o~n d'urt llzier a~tt I culafon prfedhctiom 14 re~viewed.*1;~* £.*:Uli1., fa bw;iJ' 11:.12 ~ 11 ;'A ;lik..-' I t:1'tIt' ( h-t link-. nim.jtcr i~ak ;ire prescrit4AI.
2... ~; *~ . :.~utvI.;,Ii if.'w'::j ;j ttw r;ni -itic .M lAr£1if*eaV .air- - -
i1,w w. I.''it,! U-.ovIt'J ; *a -;;mpIE , ai rbo.rric r..u~t ic atmbIrptitmn, alia rcI.fO.t ive 11( rvndai.t ive-tng I') o:iI- f at' wi -.I)( Imp'd f *!. *hir 1fo Iii',natiOn i-4 fi) V:111'( Iin cutaitgt!hin~g
' hulr liijin. ) vId ril',,mi hi, h;t mlm'*~I, ~ the optimJfum 1Lvier rj.~.1t4-:-taij
Sit, tht., 'dart Ii11h.j,' dc.ingn pr~uinfdsai. Ihv pvciitdtuntcx invit'mudofoiv.L;v diliscw'iudil okl I t *.i's. jld !.':,Ii mu j meuiL ()UI fu .1 /3j ocav Ijaiii :tt inziti.nl levols
I~:im!if .4UA.ml ttijI,.m):;hl..t i 't..,l *3(' ! tE*h1t to~ C1!t. M 1!Aii- the' Imvehli of iliwupp4fIr~i~u i
*t.:'ii., a10ird,; II'S2 e IN- if;? AV Ivalt114 val Adit.e lijl liht and~ t'xhaiuit idicnevhay are IlI'.uini-,
;i t JA i. t 'l' . A(~.1 t fol., Mplm C,i' I A aigit wimit~leth i rin untioh't101n of vaiut,01
I
Sunrarv of Turf.opt'(.e-r- , onstriitiur 'It.sts-Volume IV jCont)
operating and coriigruration parameters are also summarized. The application of theoptimum inlet and exhaust silencer -onfiguraticri to turboprop and turbofan aircraftinitallations is shown in artists concepts (if quiet reconnaissance/survelllance air-crait.
Summary of )a:tt: T iiLuiat'ons-VoIhrn 'N
All of the e.ngin. tt:t and cour1tic n:atte'ial:M trst data from the program are com-piled in this volumi. ()c,,.rati'ig -unditions foi tl.., engine (luring the tests are includedto allow interprutation of the Ih',t data. 'hi-, is a .se' of definitive data, as the engineis driving a quiet (IN ivn-rructcr 6uuing the t(.st sk, ovlE .-agine sources are present.
Summary of Nuis,' Pre.di-tion Program Users Manual-Volume VI, Part I
A computeLr p,'o,.r;,m listing of the engirn,, naise j.rwLhftion procedure is present.din this volume. This volume also includc.s distussion t,f operation of the program andsokne samnple case.'s.
Summary of Duct ')c.sIgn and Attenuation Prttram Users M:nual-Volume Vt. Part II
Program listing.s for a the'oretically and an empirically based duct lining designprocedure are presented in this volume. A discussioh of the differences hetwt-en thetwo procedures, discussion of thl. operation of the programs, and sample cases are
also included.
Comparison with Similar Papers
This report must Le '.on~pareriwith papers In three arers: ") turboahaft tnginenoise predicton, 2) turtosha.ft engine nuise evaluations, and 3) duct lining predictionmethods. In nhe turhoshaft engine noise prediction area, the work of Smith andliouse.16, whih' was used a.4 a refer,'nce, cannot Ix! considered complete, althoughIt was the pioneering re-port on engine noiise prediction. The work in progress byCeneral Electric•" Is a more In-4hepth treatment of turimshaft engine noise predictionand als,) includ h.s :in ,',phtasi4 ,n sourcte nolse and how the sources can Ix! suppretas.ed,whilh this r;,'otr c'mnphaislzis the prdilction of c rrent techn.logy vngtnes. In the
turbohaft engin, ni elh' evalual ion arva.;, mainv Itest. have l..,n conductcI. Hioweve r,thi data in tfhi: a report is w#.II d•icuminti.d and the engiae was driving a quiet ldynamomm-eter, so th: d.ata will 1, of long term value to researchers In engine noise. Mwuly duct
lining pr4-diction methodls oii analytical or empirical nature exist. The value of themethod di.velop.,d in this study Is the remulting computer program, which can he easily
used by other duct liner designers. It IN not clear that any of the duct liner pred!ctlonprcx'edures art the -,st at thti time. Many comparisons between measurements andpredictions ares shown which verify the accuracy of one or another method. However,
oodrue of a prorpisor aa well as the wray inl which a duct lizer "f-Ae on* ;: ,r~~;v:~ '..~~tIi c4 ~rietlywwarsf.ocd arid tber"Icre aycurrenat pra-
~H~r.~~~rc±will hz.ve 1i;Muiira.c4 . T!w coatlnoilag wocik by Lc,,th governmrent:1.1d iniiustrv rcetfarchers will. L& roquired for tbe developmien of accurate prediction
80
flu, P. Y. andf .Ariki, It. N. ' " 'N P di ion " r 1, nail,(;is Turbinte Engines'", Intur-Noui.:t 72 I, ()crdings,.Ortober 1972.
''his ri.port, is a preliin.irv rk. as•. of part af the work described in detail in AirForce Aero P'ropulsion I..Joratur. "tchuinwii littport (AP.-'PL-TR-73-,79). The objec-ti .-if the work :-'-ported vzis' t;, .i1 v, tls.':, nt ,f noise factors tc predict the combus-*ion nuiset of .nmall gas turhbne.s. I . :'r..a.Jwun which permitprediction of.c-DusUt po'%.r h.:v' i g.;.neratth-i 1 a giv.n ,!v,..gn ;,nd farther, to predict the effects ofchang;ing engine (Icsi4n parinct.,.rs. Th- w,,.:1 .1 :'jrfx~shaft engines is of interest inhclicopter noise prt 'hi'tion a;dil s i. dlwi'i.,.,, , .. .
Sun;marV
one of the most significant sourccs of nis, friom m,nall turboshaft engines is thecombustion process. The tt-nperatiure, andi'ciLV, Aica , l3lty gradients that exist inthe high-speted ronbustion flow cause a vharý.ctcristic low pitched roar. This com-
' • ". ".-fl -j l' i I Cuym') e'x j.,cnOt;e.nun ioinolnt-d by interaction with thebha-des of the turbine section.
To develop an understaniing of thf. cngine p:aramcters that ecntrol the generationof com bustion noise, two approac hfrs ha% vnLen used in this report. First, an empiricalevaluation of potential noise factors aitfeting exhaust noise was coj.ducted. Second, a,Amilar expression was uJts*ivi*d ,|m.-tnsit,nally based on the energ.y output and this factorwas cOrnparc (I with data from both conlhlustion rig and engine tests. j
"Tie equations ic vehlit'd provi'te a method f,,r the small turbine engine designer .j
predict the acuustic powvr gvni-rat d by .: given (it-sign and also to predict the effectsof changing design par;imntt6!r. llovcver, no attempt is made to determine the dif-ferenc.(n between rig and . gine results.
Comnparison With Similar P':apers
This papir is disriv.,i from a;srrdtt AilI~s'merch Iteport No. S. I). .005, May 10,19%72 1y flu' vt:ensm autLur.i. if covers part. of ithe work described in, uetail in a sixvolunm, r-i-',,- , alli, "Sruaa:i "urlaine v-Engin. Noise Iteduction," Air Force ReportAII PI.- l't - 7'5 %N t ill, in i,- .; vvr:iId :authors from Aillemearch .Manufaturli;i' Co.in P'•':i. "I', , 'ri 'iLtiosi I', tor *l'vel'ep.d in Inli . i,:ipt'r Is used lor core e'o , ins± noisepr,'tli.'lon in :.,.h:i'fv, ,t .ai" . A -vtr)u.;•ri:a n if this correlation factor with others
f.o, ,'vil!-,1J,.n vftj,•*- pr,.,t ion by Kazin, s. H .it ind Snirilng. i...h,
* �: .. ' - . * *d -; .. &; � .i:. . . . *. * - , . - rc:utlon Is �oc sixiwn to tr hit:12ca038 to.. .�., . - *,.* tJu .:,2t.
1t [-Cd '1.Ih..r�Z�'C r-otwcea
* - . . .�s... . . *. tc:st Uj..&.. 2t:., .,a' CZCVc i:ttLn .�
i
.4-'I
.3%
;�.49a.9.
I.
ii'3
I*6
S
'1�.
Huff, It. 6., (Clark, Is. J. and )_orsch, It. (. , "1I.turim Prediction .tL,.d for Low
-rufjuvncy (or. -r:g. Ni.-,m" NASA TMX-71f,27, November 1974.
Pu rro'
"The porpose of this• paper is to select a low frequency core engine noise predictionmethod for interim use in the NASA Aircraft Noise Prediction Program. A review of
the literature and compilation of numerous avalIl:ble procedures shows significantdifferences in prediction methods and suggests the primitive statL of core engine
noise understanding. The prediction metho'i selectcd for combustion noise Is derived
from turboshaft engine nois, data and is of p'irticular interest in the prediction of
helicopter noise.
Summ.ary
low frequency cour engine noise hias been oLserneI and measured on a var!ety
of existing engines. However, the core engine noise is difficult to separate fromother, more significant noise sources. In most cases core engine noise has beendeduced from turhl,f:in engine tests with suppressed fan noise and operating at lowpower to minin: ,ie !#,t noise. Jct noise, estimated Iq existing prediction techniquesis deducted from th. total engine noise. The residual core engine noise is consequent-ly limited asid (if questionable accuracy.
A survey of the literature shows in general that the source of core engine noiseis internally generated. Some of the probable sources are:
I. The romibustion proe.t ma
2. Flow around Internal obstruction.s
3. Scrubbirig of the duet wails
4. l.ocal temperature fluctuations or hot spots fowing through the turbine and
A number of diff.r" 7t correlations ard retulting prediction Rcvtmes have beenreporid eoverfrA llirnitted grouing"s of engn•w nizen and typep. A vartety of parA-meter- , ith dtlbf.',it s, wr relationshlips have bo.'n proposed froim results of engine1,.4ts, component lu't.', aend thiortli ait studies. The paramet, rn iffecting core noisewhich are, mott fri.lu,.'tly found In lit,,rature are:
I ( %,in•tls, itIn',. n.il , r ti inpe r t• r eti u anil fi| inm'raturm rime rnis•,d It; .•wov 'rifrom "2 to 1,.
-, %',;~nbuuti ,l l ha i's Iw:r p•r.'i, 4tiv'i i ;anil p|i-'v1,iurca ratio T.i O df ,I power" from
I to 3I.
113
11.., h..a, 31.) i- :% ;.-I -Ch 3. :.'.it ; Al r: L i n ho. irnp;,mc t ia cwvrain,.7
:`1 :.4k:1 4. itV it n 14
* .i: L;'1 id u.fl. J ' .ia .. .. ., lv thc: U';: ; ~.n ivtin la that (A M.ti ,rr for Hthe
U1.i ,11 o 'siv 1..4.43 i - L;J.. iv'.eI. Aý;dck1 cutvi.i he dic ircutionaltly :rld
I&nt k14 01 A ) .. ! ,1(1 .1 wv 1454 sixii t..3 i.i vz~svtnia i;i1 rhe ;-SA j -p'.icr ftir frt.. : . I: I3 '.~.s f;.sv t.- pexsk tit Ow~ s1A'('trum 1.4 ak.o t:lI.4al Ifron Dwan. antd Po',ut
4 O~~a *.* .43~3 .H 03 ;1-t~ fi:1* a [).-:i1. ,I,( ii.-fCv (,If .11)( j~. iw sub-Ii Jt I k JIt' iw : ias.;sV f,1.,;: d31jul 3' lilt ralnrs ..f 'til) (1) 10:1. Hi.".
I I "3 4.1 .It . *. : i s * h 31 h' f-: r sx .1i .sj c *)31*lt t);J i~~ r.itilt- wnrk t 1 -tl-Ing
I-. 44.3: 5f4':. I !o-ii..1, .41Id pi't.I3i I 1.331 of cort-i ena;hi3e tia 3:4 :An vxteooilve
~~ I ~ , h. ra. t.'t 10 4 1101 pubi :Ii-ls 1;..itI proviolt 3ch p.3L:ti;.il.1 14..Uio-w in :d cm-till. hi .. t t-' Il -lU It r jsrcic -luivig C N' 3Ic 33 Vin flsI:'1'ti. 3 3n ii ; it ~ l.iit%(
-ll f., r p o , 3... 3 4w.. I 33 ' b o:~ l;$oIl- il r ~ t;.1 m
I5. t .1533r Lit 14343 a t i I11 1 4 1. iv tm4.~~~~~~~ i3tn I.'4:4 ICA13&r~.1s3 : 3'tej,1'~~i~ii ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ -I A 13 ',h34 p o...*I cosv wnt: I 4'pif I54U3 I t33 3.tIf1iI till. v3t.13 .33131, vit 34
4 ,1. 4 ' o il lit itI'1 I34 Il I j 1 1. I414 3r 3 I 434 .iii' 1 11 1ol D4 I43 !:!i v I1.4 I3:I I:43 I ftl
E,.luation of Paiper
The equations and curves contained In this report permit the prediction of coreer.g.ie noise of turix ihaft engines. While que,3tions remain as to the validity andaCcuracy of the method It appears to be the best available at this time. The procedurehas the advantage of simplicity and commonality, but is probably limited In application.Continuous improvements in the method can be expected for some time to come.
The review and summary expose the problems in defining and predicting coreengine noise. A short overview of extensive work In progress, numerous recom-mrundation, and concluding remarks constitute a valuable commentary on primitivestate-of-the-art of core engine noise.
'I II V..
.'. TA I: rs;i U! 's rc pC~ : I .YTiw. co I-r t;j, os s
C, VA 11 Ic 'k 1:. W.t 1..i h. s...a1 1-hi r *rf 2'lIf2 i
'I Il o .o 1. 4,11 ti1.
.2i. tit.t*. i.i~~r;;j;~~I~C e.i' 2;:~ k
(%,; !ls di2 ii-.; ko n s4 o i.f~ - p r - I-i a e
* ~ . .s:i?,, . ~ri. 1v ! , ,nt ! - peed W uas not r nv mratio, II Olt.; iL. pro-
0"1. Im i pr..vI. uniqu lit t*Iim- itic fud.
1 .. 5I~ 2 .*j 3) S .411 -1! .! 1 rz1Zt-Laerr.'cI ,it t.41:4o pro Inar:2bo -2cr it-.
;. I ht l~~ 121sit. 2 . .' 2S I5S.iIyrvwtS'2 ofr .0) f ms 10,111 ove a~ I2) t -s'le
m.1 110. J11:114. li Ow 1-:111 si ! I ~IN I.re. ontvilc' burnerM~a i t a IJU e
S,ýn-marv' (C'ont)
In order to completto the predic'tion procedure, spectrum and dlrectivity haveI.). tAt-enr preparvd. These were derived by examination of data from all three types
of aingi,•s and component data and represent a best fit to the data.
Comparison With Siimilar P:.pers
This pnper is d,:,ived from recent work by General Electric under DOT/FAAContract No. I)(Dr-FA7"WA-o'1023 1 3 . The emphasis here Is on understanding coreerngine noise o, larger engines. In contrast, the work of Shahacr, et a12 7 is concernedwith smnall turhopropulsion engines. The resulting prediction methods from thesetel, rences dufvr sil,ni!•h antly.
Rt1sults shown in this paix'r are Included In 3 3 volume report of the G. E. workander D(YT-FA72WA-3023. This collection includes idertification of most, if not all,coanponent noise sources, noise generation and suppression, aad prediction methodsfu. all significart nc.lse sources from turbopropulsion engines.
F valuation of Paper
This paper pri, :nts new information regarding 'he corre"ation and p,'edlctionof core en•ine noise. The discussion Illustrates sorte of the difficulties and uncer-tainties of available prediction rn.,thodn. Slnct- the information here Is limited thereader Is referred to the final report.
o7
V..:.I ii ,14tcli GL lic..,1 iEuport to t-he FAA (Contract Dc'r-FAA72WA-30)23)
.1 i;;~:':±n. ;I.~* .J1.i...i~ditu1-lig to (.' ir. No!!iC.
3*C U. i*rk :1. ,j IA, :ý d-irditve, sumnvirUV m-port includin~g thc hatf.SIII. c!:I: hug i!cljia ~, unt Cifling utctc~ ~and pri.(![ictiofl ieethodas fur
V. j£Lp~ 1 ~nt.,.u c.~of J:arc nuiA.;e :c e widi prcpwgtio. aOfects.
ill..A1..L rt:?.',lI. t ~nSIi'-;f fi(4treve voJ~lumes as foliuw.:.
A"umie I -I. kentificaiton ul Camnpuieun Noise Source~s
- - u]:i.: H ii t !-iifiatucin of No.5e s c Giuertitn :and !;-upprc;ss1un Mul.iflb~isuis
%'t I -~ v i 4. - jo-mfcat itn J~ Cujm1!oz~vnt Nc~kti -eSourtris
i* .r I( lviIt'1-11:11 cuf.! 2 zIKg.al noui.;i` Ai. 11W CLOfruIHjUtion from' jet Iii-)h, c'ornuto~i.r
J~~r(-.:!~~~~9ant l*JIjul~I4, ~i~: iiji~ip.i :-&-w. Ani hivi-AVi4iZtion wi W ma.4 dl.r to
d~t.-I rzln ir till ;-vilt-ral a g Ilw( 1 -ragi-;rrin , ceunzriJjI hu v~anrabIlQit, tile- ia (if ident ificat ion,~,and lthe al-tec- III vn e bwi duig,, i, if reiductilnl %ero~ reajuirt-d f-or v*':aela e)ighta core vngine
£111.ICe SOUrICes. 'I'lle vial imis !.~tru I,-;~ are! ev~altiatec! and rark oriltered fly predicting Ilmwit, .4;'(11triIhiarm AJ thi- itA,'virlivil comp~onenlt,. bv Il2w me Ititifni tcivotlP( 'urirtg the ('ouPtr~qe
I) ,1 "'ieIiUAII '.3oIn I ('411t ii, 'l J : ?iro- I') on;( arvIV aaill for -;icsh (if
wii.. ;'tutil ;,I wo~ I v. for 1,-. 1 j.I.i.a of .1, 7, andii 1 IsýIv I. I it IV , wI hih were-
ftirt:ju : :I~o'f to ai-ivoin;)w.. '.1 if coa;,a' lithu roerdmual arer~dt powerplatnti. . I[ Is~ dttleri-minud
t! i (~u~lj.f'l a'Inoiss, 1vt iObtlj, I adi .e hiI I U rime/1 je~t. Erta-r~acton IflolaP- andJE ohzj4t flW -
1;inj', f itii' ,;l - I fit. i1 :1 0 j 11. I[.. J.;lp IvA -..:r.I- f whilel vaF.eh r Mvcba:; rompre
l,,1: '1a'' !0 Il i'i1jj:k'jjII~ (i,'fl;; .4. 1; if).io an 1I()ll) ;an:d 'lit rin %1r1lzcbfmI pro-
.~dIju'jlsI~antt.IN)alii :eO...Ulta 4~ in~alyf~c;iI work to titlee-mins., Ilt& Isadev Iara.,1t4r
1,.ov41r-rliig )I(! v n~huIw! nilt -4in :l o.Te n'titiIli; are- ;',ven ;n gewr5':r formi to toii
*' 11pj ah;:. to a wiItIv vats Iafy of .~me
\',.du; It - ,-ii.n: lfif',tni, of NOisCr Generation and Suppression Mechanics Cont)
Suppre'ssij: , ncets were identified by analysis and experience with prior sup-pre.Žsion stu,.i, o .i huih velocity jet noise and fan/compressor noise research. Theseconveptb were" v'.liLitcd through mudel, component, and engine tests.
,'Jtailhd expo rimental results and analytical evaluation are given for the following
ralJ or ,)ources•'I l tr0ffh.•'u :
Jet Noi-t"
Cuaxial Effects
Suppre.•sion Effectts
In Flight Elfecti
(Combustor Noiie
('ombustor Noise Generation
Combt~ustor Noise Characteristics
C(umbustor Noise Suppression
'Turbiitne N,)isc
Turibine .\oi4e (Generation
Turbiz;e N'nee (Characteristics
Int r;iction Noise
01)hit ruct Ion Not , --
(Cats ing aii'iat ion
(Cormpl~remio." Noi•ei.
VhiIuce Ill - I'i v'olt Ition MO'h'odoi
I'r *dhiit it lhiii! I,, Ii flor c'orTe enJlgn!e not N'± ar'e formulaItedi for low velocity voannulairj0'., -oirnh~iit ,r.t, !ow preiiaurir•t urt-Ineit, ir.tAsir•eition imltween tirline tones stage-P andfn/'or, ji'l ,it ra;ioi;, oIPr4tionru'WOn In the floiw pamatgem aund casing ruldlatlon. "rhi,dli vl')opocint iu- tt1 "d ,.n an anliytical lnvw;tttli!o'a and rniAe;, corominnt, and vr.iine
tent deos'rll'im in Volume Ii. rho reoultee are In letnaral form to be applicable to a wide
variety of cycles Intluwling present and future turbfian engines. The prediction methodswere validated with measured mcouutic ltios where possible.
Hl
* ;,j. .,,,-, jAzi %, .,nvfni(flj)m~ and is related to
* ~ ~ ~ ~ : A, ..- '. ~ ,,i rut. thc .wi u jet or-. lA
* rt. *. . ~.. -A .. ~ %.. L! bvl b',5t a :Lr1 no e ~ jd.-itv rat io &.if the-
* .. L~. I PL e: m .. ~a.. .. *.~iiu:iA to :.Li-r 1.,wL- w~it.. air flow. r.4t,. ,
~ C~Cicw.p r;.-Uirc ri.. r;, n: triom zii.o a. u:t.n. d ole. daie:,.IL
* n ~ . : . . * .1 ~A -L l'.' . hth e IoJf s .1 1 ( h i l ~ a L w l J`-. f -2 L~ ~ 1 ) 3 1 t a L rv t , : tr 4
* ., 4 ., i p ;.Ii . .11 :,haip, . I~ tI tV ik nlrvt:icted frtm flm .::i-1 u.: 1.~
r.~ ~~~U w,.~.~. ,. a3m:~~ r thc. il* diction of turbine nuisv. TlleLss, are: I- a
~i~ i:Ii ~ ~fIl- in. ,, It.) i :! !'Ni. Ltn I:.I.t~L.Utli' ,l :.4I f il Q)aL n i~i W pLdcE f - - - . . . .
.1.int:;W. Pit. t 'Ah ln: .,, ilvt I Li r .-1 ain1c spcc(:tihn1s andic :) k~ Itcluiuc for evaluat king
I . H . 1i .::1 hi miniPcI dl j var.. .m riatfions tni the~ tnioa. gc'nt ration. Tia'
ir~int aI'.01Iii. i; pro.'. 'Ii. 5 ur prfdl hifigiI lA4:JI Iisc, speLctrai,an
I h zgt~riat1,11(if :1 tll how t),w %%-til Owh fha,`V W~~n.. jet :trvafl tur1~t'iencti~ rinmiutL1:i :1 .l1.-p 1.1 'hl. p, ... t111 piA : W.ir A:ii.d ilrla fill the lla 1im 1 .6ildi dth, Thi.; I.
ft h........1 .!.t . l~it1:1 mr ! ai, ui clsiulges ill lULudiI) ii ai a.wt. nnIC:nd
dir.., tlvtýI~ m af- -jf .in a tt JX-1-1 vjivuf Iif) ;J.. j' fl'dii tionI lunvatfI: .1iWl pi :e wt'ei~ d t.) de1ter-liii1. till uI duu-itaon in pivak loi:,e stillI OwI fri-quen-,- .iprc..m6ing. Thei vorrvlation is;
*U~d I..6i .. i'# .. I'I- .j.Ipproxiatio *I.LIiil* raddit loill dathn *dom :l ilatdI IinjmiLL enxt
HOW~.. NO) ollnein'i M-C ;Irl`0ViIeiI lo ýwc lilt-Iu diiIP''tivi1tit'' thsit* no~iv source.,i.
*~~~~~~~~1 tvh:.ei;IL l'iiLia,Ju 1%*j tt.aali~mAl~l 6 all ha1ve a1 ~t~~il.q.srlIt. 4aIfet t onn-i'li.s* ::ci* A. -ill, (tilimt! (a:; ng radvl sina I' : ina i wi gictly 11101tla tIoi-iiI !.(tiv .t o ut lai
Im~f)I * *;iI * l p. .hin .IhinpiII. 41 p!i 'a1lrm tini proa.irilIr :i. *Iha' 1 ~ it -tmi~llI-1
P1il I;,~a 11i-l Vlul e111 ir WhIch r-jireitien't i thit work doni- aon' v41P It4~inine foke. tt"tludIs
ýnp.. iarisn ,k ith Sinmii Ir F'fa,!rs (Cont)
a: (;F. over a period of several years. None of the material is essentially new, buthLis been revised, in'proved and va-lidated with new and additional data.
The report collects, summarizes, and updates information spread through severalIt'1"t' l'Vr ICC.'L ..
i" a!:.ati •n of lk:p1 r
Working equations and curves are presented which permit prediction of corec.n•r.,, noie using red.ily available engine parameters.
It JhoO. I b* emphasized, however, that extensive research work contliues inprogress at many centers and that analytical methods are adt advanced enough to pro-,idh. ij,,neral soiutilons. Updating and revision of the recommended prediction proce-dures will continu~e.
v. i. I, t .I L: i.. I :it; 3 In 1 :I'C tien lgisst:.. ri rim
*im A reie **3*'33. e.-
EA u: uz~: v1..2 3' 1. _ i .iali-d datza r.. -7 1 4.ý hA tht-.v ':3g ~ e
.3. I .. **Iu~ ,3 ~i~Lfi 1 A~ .:~to coi rvdiat turb~ine mi-;i-,v i ;irvli, i.ttv
"*nd Fp.1:2 :1i . I;,!( -t io.1 'r I",' P;-.! tQ1 . *'i.' 4111d o~erazticmna I pni raint-t rs.
!1 .I1i WOVI.:. ý ~,.I i lljlcates thIt tluz; 'ijr.;t pu~illi.Thtd'" "I. t~ 'IS:: 11i.. X l3j III . 3jt.:Zidi1pt~iiou thst tu rlirtc and lan fluiseL g3?Iwra-
Il a' A J.3*..1 .ý -r -1' *': i . I -:t '.. S:' 4 (Eir-ct tunes, and broadba~nd noise.
' ~ 3 Ii. .. .~ I v. ii.I ..1 *o' ki 1- .1 to 1. L32oa.m3.323113 .-awre (sri %v:ts 131,itvt'v1 iii ,-orrellktinlg
I'! -A 1, : A ; I!.1; tI-mali lIi 'Iii L~.i 31423 da..i. I3 I).iZatilc;32 of1 data1: poiflt fzr.3r
j~j. *'~C. I I I., WI .,:3Ul I;; pi'. I i;,3r Oit- iurdamia3~~Ilu3 ;'14. and .9~ d!S i3l Ihi'11.1.1bld;
.%Oi13! I'ma:3 ii 4d.t thi ma .ilal-it- ;,t N.kXA I .twk IWt.':t riit (viir twi :.a'vvral .i ra tt
2.'A W3 1*~'3,, .1 10 01.3 ~,i''I, I l!-th o2. 2 I 3)? n a~3nd Pzit13 '2rt. The vin)3uptri.im is in-
I"33i, Ili 1vv' :m,i.l iil*1iu '31114111:; ac. t;.ti prP33', i f~in.; w i''dd W,3 1e.''' fi3r turl3ru3.al tI-~
h33 fill- ll~ hljV333.Ii'jI.llI41 elu f 11 e~il,'l:Wll till, WIl~;~iie lraraI.3 pj)Ii31131iof
Ills~il .'2''3 \ I32332 .33.I I'3 ii 3 C33~.'3?33~l3:.1 it* ml ri tc31C 31133 i.' IL,.. N :,-A
1. A23 A33 . ..* ;.'3I' Jill.- I't, .li.i i Ho f tie I of' tl.c' :311A3,3 Il i ' ~r l1:3f 3r
1.' ~3:,f .,33' 1233 4~t3'11,33 l~I2l~ Ill p4rui pr)341111o 111iti laW'. 1233111 lurbil~lo h3,11l2t" 3 3.A d j 4 lo11 .1111* ll 1
o33.' .111i low -.1.. I y'i'. 'cp i -ar~ x1; t I3u2.:i-io 3it ii,,i!.t, i13;mi 3I('rl q
I1-I
(>,rsparlson i'trh •)tt,.r Papers
Thi.i pip,:r revi•..'s the work of others on turbine noise and selects w"hat is con-.-icrn.r to be the bi.st avafil.atl prediztion scheme. The review does not include the
l"te:t wcrk of the ut. •AA Core Engine Noise Control Program1 3 or Mathiews andPeza*h: 6 . T'he .. aIded results of these more recent experimental and analytical,'-.," itflons s.hould .-,iuific'antly improve and extend the turbine noise predilction
I~.v.alu:,ti. of I'iper
turves inI figuac.is are presented which will permit prediction of far-field tur-
n, t,.�: ~ewith limitt-t t-,rdii•'icre. As a temporary interim approach, the predictibonpro,. .,dures offer the advantage of -•implicity and commonality. Piblicatictn of morerecent work will prubably result In significant changes In the pretdiction scheme.
93
1~~ 11E i '. tu L s
* .. : .. . .. k- i .. iv uir Llast and 'o1r tup~ ~ r b ine, jet arl`:d --
¾i'' . 4 ,!1- .; j'* .. I . l:; i~t~t 2~ A
'-21 !It.!~ . ~ ~ .h.1 .. flit az. t dL~x ' w hic ;1,Lý l .
112~ Itvl~r~ f. 2.. i ll.2. n*-.,:ie r cJ'2 Ig n. hawL~f ;) r nvce ~ , 11.1 2 'A.. * i
I..' r.: :. p;.2r-~I.*\ ~ .t ;w~tjoxt uf work wifai I en (Joflo wh~ic .Lris that n
.. ; :.2Iri !P'::,': Zo. - ;i1:%i) :uri. t. Irmit~ !h cLk :uvel; sthe Itiadirng - 1V. -. J 1 21c I .p : II ,,. . . .2',- .11 ;10 01a.1PuLMr 1,41 byV Iaf-2fI 2c in
u~z2 ~:I*!~ lii: aitA il', sIit Iwihopu'i~.r M0,;:,2 'nl flic e1(,xt-c1itao,ýtrn2111ia-
;;1.. 2 1:1 ':lfj- I li!% l i2. *j 1. S.t tU 10IVft .J~(2:Ii''i ~l'fl w2; . i . I m ...
' .. 2 Anald 'd! do., :,, n;pi..ii. I rtm 12)2,*iIr 'ii ii i ciw -I, Ikri t2i~c! .'W-ý
* *.h,'.'Ili-It'. f i 11!4- li i'.eu w& -:. I.v-j l w.aiIc, lI~o prv::or~t :t,&.,.AirI wif
I tfl :rI Ii2~jgi ~s2 !.r hej(. Is. 211 a -i t ' ;ai b'it vqtrdi inwt'rni~t. Ai
2 !',.~ .~* 2 I: ~ *:114 .vm o I *uill Art,'~ . -.,i I - -J ii . wi l f~iI 2rom22 fbi. r'r
-:w, it .I j'40's 12.11II If*
2;,! .* 2 r-., . ' -all I:1j212 I mt1. -miruc2 dI vili'llt,1,Il f,:
T ! I .i * it I.,. 1*:1 r ': ;Ail
I: .~2. :II uh I,' .1 'ut .2 hi t') d, III illd~ .11,1 22;ij..I rdwit~22i~ 2
-62P ICI 1 ,.1 1 w 11; ,I i, l
)I list, mati-rial 1 m~~~tlo-it1-1d n cO il m h I,
iv .
M.!..4 . .11 A.. '...\, *r(:~ in ('orc ln.,-rw an,! TurmineNoiseit
.. h..u... , , AA.. ',.r . I .- ts7 .
TIhis p.;Per setr~ef h ~tw sn l1I9,4 -it-ittv-tf-he-:srt in both core ergine andtu~rbine ntusr itvvt'hn'lI;:v. 'I he o h:i r-ir tvristi' _.tf lNoth 1(,w fri-quenc~y cort: noise- aind, i,.,h Irkt,.. ~' tus isir.. ;it ; : -wi*v e dlel ý n-%v~''~tral p(A,:sibIle noise g ine ratingm.e( hanri:'ri . .are ijihid tl,~ J. itcults of a tv.t p.rugran- using a vr~3b turlwAin engine
a rv ls rilwd %%Jucl. L..Athr i cli t ti 4i~ m:is n. sos ources and propa,4 ration. effects.I
\it- v onteol (if ~'u*~:iz.t:- ih, jiv*ed for I :rthoi, r r''-.%arch is dsused
I ,ore enjgar.e fuise ia, tli.,t g mwratc'I by a va.rikwtv of components inside the engineL
ga:.s i~tflvatur adnt ex~haust s-. vtm, includiig, c'ombustors, turbinea, and flow obstrue-tionh. l or thme pur-Pisv- uf thi% Paper, core en.n.irc roi~e i~s defined as the low frequency
1. Di)5v nod isej from tht. 1urner itesu~ling from pressure fluctuations dluring
:'. ln'irtci huioncr nluij f'Irom velocityv and ittrrm-rature fluctuatifons4 inrractirigW&ith 11it' i ii mii.,
3.Ni)!... djueto)Ii turlIt~l-ieitt atoll wwirl in the vxh~atit.
1. Nolte gvnitratc'f At the nozzle' lip by Intvraction with flow turbulence.
hart ct (tilt, iii:,f itipi tu.1 i4 i1 ausel ly-tl.- flinit unste':ttiy heat rot-Laqv of th- (-on%-b uithion procs:-4'. Thei' uotidjutgit, il ri lnw Is hlfghly- turhuient andi the fuel sprav eoflsasfs
Jof raondom mi/vditroeibis ~. ~reIprtei'x:it fluviu~ations Iinllc~atw a noise source whichma v proliag.' te hroughl IN eng~wsftamtineI comtjOnn~ts to the fitr-fleld, Quantilative44 tiol Ii tems of diirl-vt ' ~itutfi. n o 't have hc'e'n illtricutis to ehi a in, but thai source inustb~e f, -Adrl'le !eil ptfnli ~k~igis i ant.
l,.lIi~et 'dil'I ~. o~~m- t-of' bay Ow, -rav.- tti,u ili litirte gio ,*r ate~urkli.ssrCit';an-Ili f'ngoer-if'ro Iliv. 11i.1tj'up; DI.!,; lM-n tv ~e:-, /,-,I tit e~. r etl se ' I th'ire'lci :i whrlen_.
aneipt lxJ41 at rw'-I' a [ms dllo. ftor- i: s,.ha'm1.t noiul/ It. if) tNMisae 1.3 roppty.ut Ii' if(11ti.W.,V413 l'Iti tod, I)( p- ' ra a.rId jt4, -v"Isv.! :,r Wills lts i r dif is lst h I: is I
..' ý lhil:.rV u("Untf i
-t 'ut niise is caused bY flow impingemient and flow separation from struts and* th. r (.I1.L't il thOW L'Xh:1Ut .tr'::m. EIxpe.rimental studies show this noise variesý.'ith tht, sixth pwer of th, .xit vt-l Itsiv and m-a :,v l•_ dipole in nature. Quantitativeroc-tiurs. :1'c not av'.tilable for prudicting the noise generated by separated struts
.'A a due't.
.;trut nloiStU it:v also 1e, "eiv•'rated b. flu.tilating lift forces induced by turbulence.Thir, ,ppears to be no veriftid technique for predicting noisy by an arbitrarily shaped1h,-ih in turbulent flow within a duct.
Nozzle lip noise is generally thought to be caused by the convection of exhausttirlulen'c p.ist a nouzle lip which imparts momentum fluctuations to the fluid near thei .- S-vvtial theoreti'.al and experimental studies have suiggested lip noise intensity
'.:arivs; with the sixth power of jet velocit.ý. Cross-correlation studies have verifiedthat this type of noise produces significant contribution in the far-field.
lar-field noise depends not only on the strength of noise sources, but also onpropag.ition through turbine blade and vane rows and through the nozzte. It is unlikelythat transmission problem will Ixb solved rigorously because of t'.A complexity of geom-etrv and flow in the core engine. Studies have determined that primary variables arethu mode order of the inc.ident wave, the wave number, duct flow velocity and tempera-ture. The structure of the shear layer between the jet and surrounding fluid is alsoimportant as is evidenced by a difference in noise between single and co-axial exhaustfluw configurations.
Because of the comphxity of the core engine sources and the torturous propaga-tion path, several prediction methods have been proposed empirically relating corenois(s to overall engine cycle parameters. These predictions may not apply to allengines because of significant differences In component and installation geometries.A review of several prediction schemes shows that these should be considered to-bepreliminary and further work is needed.
Some preliminary results from extensive tests of a JT3D engine are shown. Alow fr4!quency peak centered at 400 |lz protruding above the predicted jet noise spectrais identified as core engine noise. The general spectrum of JT3D core noise is de-picte•t, as inferred from many spectra at various angles and engine speeds. Cross-correlation techniques were used to confirm that low frequency Internally generatednoise contributed to the far-field spectrum, which peaks at about 400 Iz. The mea-sured turbine stage velocities and pressure drops, together with the rms temperaturefluctuations and the characteristic length scale of hot spots wtre Inputted into an in-direct combustion noise theory. Predicted power levels were in good agreement withexperimental data. Predicted spectra peak at 400 Hz, as did the experimental data.
556
P. : .I', . .. ,' , .p -1 .4 "t. o': (.)o-ltJOJ i1zi ar. shown to correlate well;,::h p1i m Ia r I ] •.a .. !'.. ai,:iI.;l.. 1 :',1 t-ngiva, noisq, levels increase ' ith velocity
It. .y: L:,iUl,,hi' !i.'. ".., .,. t*. :. ; .T charatcristieb of corz. engine noiseIt,: til .1f: Ik•a :'.." ... i. ".. . , , h.0•..s in directivity were ohserv•cd with varia-
\.tn th,' vrt, r,.,in. v-h:-us,I I... i,.. .•irroun led by the co-axial fan stream, a-tediuttiun ..4" I 1., -i 1 wa:. !1 :.t . aiq,i. of 1"'i h'um the engine inilet This sug-ge.:ts th;at nf./zle h...;.: uip,.,I:)'a t-v uW; atiaf... .,'t. :allectd.. by the external flow field. At-tt.,pt.t It) deit hla)II't. !h- I ,litrilutla,: -j! lip noise using the trailing edge noise analysisoal il..,I,.n2-', vl-. '..• fil, " t u,,,Un thet. pri dik'tod spectra peak at a frejenc\v of4100 liz. Estatblishia,: th.!- s.ig;fic:,n, of lip noi,;L. will require additional work.
""l'_ *rlif:,. noi:.L' ah.iSnatlt ,ld . ,.0rbini, tonres witih hrrodband "haystacking" thatitceur-; in th. r.gic n ,!t tha tone.-s. I Jr":-in( u.nae.. :ar" a':* rated by interactions of rotor
w:aks'..% - itti d,)wnv.: r -.a:i :.tators as..i I wr:o itans of r.-.ho'" w"akes with downstreamrotors. ()thcr sou,-, t. , .lis•.rtett- turbine ioncs may include the effects of non-uniforminflew Imro hurm'r .,u.uvate.' "hut spats" :ln(l turbulence. Factors affecting turbinetonie in.e.n.itv ainluhie rtea !ape..d, atzgIe work, size, turbulence intensity, streamdensity., nunill-r of andtalcs, -n rotor/.ltatur spacing.
Ri:'ent evidt.nle saiggest that "hay..tacking", the broadband noise from turbines,is not internally g.n,.ral,..d, but is related to the propagation of turbine tones throughthe turhuhlnt v.ha.'s, :luw. (;rowing evidenc,, shows that "havstacking" can Ito att rib-, .sd !.) scattering of turbint, tones by turbulence in the exhaust flow of both the coreengin, and fan stream:•.
srveral current prcdic-iin schemet's are in use which are based primarily on.mpi rical cot r,.lation., r(A ti.t data. The procetdures follow those devwlol:tyM for fans
and compressor.. Pratt & Whitney has developed a prediction system O.y correlatingdata from JIll), °i'r•'• anif .JT3D engine. Significant tolse reduction iu possible bothby modification of the sour",e :and by using acoustic treatment in the primary tailpipe.The latter, is |,oth heavr and expensMv, Ibecause of the extreme environment.
Mi:asured far -liu!d tur~i'ne nolse spcdt. a tr1m I IlM) tests were examined and acomparison to. prvditions from the P ratt & Whitney procodures show good ieorrelation.Th," vrrl.ition inchi,4 a.. tht, effrts of a 4ignifi'ant contrilaution of the turb:rht workparameter.
ibsa rý,vd dif&, ra,'n,' s ma turbiinc !nui:,. :p-lrtr a ar' llteli!-('fvl relitd to difftern'(L.asin the evhaust flows which the turbine noise propagates through. When no turbulentshear layer is pr•.•s:nt, th, turbine tone Is highetr and the broadband "haystacking" is
9i 7
.Sa ii: inl~i r'• 4( '.fl
h 0.4 p't.I-Vlnt'ti than in sptlria obtained with a coplanar fan stream. The tone energyis anatttred :i redistributt-d to adjacent frequencies by the added turbulence in the,.in shear laver.
Comp:arison With Similar Papers
This paper is derived from various experimental core engine and turbine noiseprograms, including a recently completed extensive noise test program on a Pratt &Whi'ney JT3D engine. Though similar in conte,-t and conclusions to other prior work,additional information and understanding is presented. The importance of the indirectcombustion noise as a possihle noise source is emphasized and the effect of the propa-gation path for both core noise and turbine noise have been demonstrated with increasedticttil. From the survey presented here of prior core noise and turbine noise tee.inoloer,together with results and conclusions presented in this paper, i t is clear that more workis required to verify and extend the range of present prediction procedures.
Evaluation of Paper
This is a valuable summary of much of the work being done on core engine noiseby Pratt & Whitney. Only limited results are available, however, and neither thecore engine noise nor turbine noise can be predicted with the published results.Moreoever, the emphasis is on engine noise of larger turbofan engines and resultshave yet to be compared over a range of engine sizes and types.
98
,.'..;l' r I;... .. , . .. . . . ,.. •.• .. ,,, P.,, , iFr, t~ Engin,. and Driv'e "irain~
[ . r p. " .1' .t, , I"* ti- .'me;,:ai'rrl' tlt ' o| the p s..iible sources of
S!!.' .!iw wit ll:! I, Ii.: . • ., I1,t, 1 I!..-j k,,:..:,i.(on gh that niJ% contrilnzte to theni.ise o1ls a' I •,ht .' , ih ,I. I nrf i i ',, l. i .a(. :.'.:,'li zk'iu-tcI• n uit'e:('.
'I fih .0u,111 !it 1 , , lA . i,,I ., I,•,a ra. ,;ai*.wzi,' r ina.i rnai combustion engine can be.l-5u::'!d lJ lit p."p '.*- " .1.41 " I . ,'0 1.. - .,i:i ,t fwe nc , structuire area, and
t1". ifar:ati:an % Ia' him 0h .... tA i'itr,.. P|rin. ij,;,i iawurt..- ji vihrl.tion, in descendingiril'cr of imn)urt;.-:ia , |.|,- i J ý;l.L;til,rl proc "es pi'toa. slap. gear meshing and
NOck injvctior.. . Not i I :%.1i:aia ml i ...... d ,, the structure. Obs:erved
:,io,'rcc due t j 1I,11.n ,|,. ,4 d. ." -;I I-wt vit'tl .,,.,
Combustion, a.lis." It r.'la.tedl to the rmal cfficienc'; of the engine. The mostaIeetIltt'cl nlvth(%.(! , I ,IWt :1,)l is 14 re'luc: .)ptratiaig spet,,. li-ton slap noise is pro-duc.d liv the ir:r,.-.: a p.Iias th;,t occur bt.twer, piston and cylinder. Gear mesh-ing nuise is ijrnost evisitlit :at Irc.,;lju,.ies., rel:ated to the gear tooth contact frequencyand is most sensitive to luad changes and the precise, shape of the gear profile. Fueliavt ion noise Is c(- I rinharilv to pressure fluctuation within the fuel pump and
Sibr'ition within lite ii ie•, r.
For a wide varhtv of dii|sel engines, the noise generated by combustion is relatedto operating sx•wcd "and cylind.r diametcr. An etuation and constants are given to pre-dict :X-wt iglhitd d.-i1vlh.l :" ht*vt froil the, machine for several classes of engines.
rhe noise produc.-d by piston slap can he estimated frcm an expressIon for the _ratio of the acoustical to vibratory power. Inputs must be determined from the physical'haract.riatics of the r'adliatrng structure and the vibratory power from piston slap.
"The noise produ(cedI, by piston slap can bie estimated from an expression for theratio of the :aou.iticai to vibratory power. Inputs must be determined from thephvsi,.al -h1arateri.sti,. o tht* radlating structure and the vibratory power frompi .iton :slap.
"The noise' radiated b'!y an automotive, gearbox exiti-d by gear meshintg can Ixe (sti-mateil uzirg -insihpc i.uatlon which provilh vi, ald l:eve liar-.ral distrilution. Prvdiettedl-vll, ;are rIl'•at(,d to t r,:,,snilttid horsepower and gear speed.
i7
.unimarv ;C'ontj
It is concluded that noise reduction by either reducing radiation efficiency or them:itnitude of the vibration forces requires an understanding of the mechanisms of thesource and a knowledge of the engine design parameters.
Et:luation of Paper
This is a brief overview of sources of noise in reciprocating internal combustionengii.tc. Prediction methods are indicative, but too limited to predict noise levelsfrom helicopters using internal combustion engines.
,.'.'~i .. - .... .,,,iI iTviperit.. rt! lHiu~tuations
thu.. p:!,MF J1 :44, Wg A.' k.. i~Pr...t I" .1d wV11aia !%) thait sigriifivatnt low frequenryv.a f fi h:' ~'~*WI.s4iIi.. Co .L4 4,1 l"1 1"(11 :11141 t'Impt'ralt.Lt' "e'ddies"' through
I k.,. ''..~-. is -N z, !. r t-iitijne. bbjI.s :;r4( vaae rr.wvs. te~..uitsfr£'': ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~f~ lii..I.~.1,L . . ':.riu, I:'u, ~1'U. Pratt & 'liftney
1~~~~~ ~~ 1 nice1'a*t *f*' 1 i ... ..I!l .'i I-$., '-vpa':K , core tojif da~ta.
VAi I'IOU'. 11-1- II.L't.'94, lha.v~t 1A.411 u4Iejp.%ý:a if- -... ptain tht, obsermeda low freiejuunevnoie-1S of turbtta... a'i.gi n. w m 1141 (*.aflalit iw ac . eI ournt if ',,I- In jet noise :alone. It isro':a .. in:taIv i~t) 4-:6 p.*1 L.i. '104 54 sour. 11r, at i rE;i-i' tit the nozzk'. whis n are pro-
.jaIt,.. tmsat .1% 11at,~.1%% imt. ractiti.g -. isi bij ait,, vanes, struts an-I nozzlev%.at. An :etaddiio,:tI. e*_1 I-[. flat, la 1 ~rge4 fluctut..'Wids in temperature anti
* :~axial vve14)4it% vre. Iv- -1 1,%',L, 1.411 ner p~ass.inag throiug~h suvvýssive turbine stages.
a *I'~~ht git'iaras .i.t prtasvrtud by Pauikett includies tacise genleration due to flue-tai gilig lilt gand Ir v . -. it th1. v~ar~t (,a bir i iii row art :iaz~tion toi thz' nolst. gene' :-atedbyv vortiettv (turi':. ::aaI 4Lltroplv auenflw raturv) voriecting thranugh thle dise. 'rh.
* t'~v)jIttrab~utiog' lut. Io, ag~r Ivir~ npier~ature is vonsiffered in de'tail. The me~thod eon--1i.*hrs sniaII un--t.';aet p'*alu rba:ti4)ns of2 the invai':n ow through :an .artuatcir disv- ta kt
* ~rtulat-sIn'ns cub.' r :I tur iia riit~ir or 1141/ /Ii guide4 vane stage. The anail%,i- .a .'lso :av-"outOls for the' large' k~ig- iII flit . strv'ani flow var.iable that are' a design fea:ture(if turbine stagegs :ainl ;I fauitor tit the noise ge'no'rating raiecharlsm. It it. shown thattatike Ievelq f1w't. to Ivnpe r-ItUre fhjc-tuet ions art- dihpefl(14t ont the' rms intensitv -andtr~arsvi-rqe' I'rtrr4+.l41)fl it-ngth ;atis t flu- , flut'tuations in ;additiori toI Meteit turbinteopeI':Itinlg p:tr:imvIvtr.,. l'aaatliv'aaaeare, the pe-iak intensity or~curs at a fa-4equtunt'V thp-n-enft on the :axlii tot rvI'atl4io Iv.ngth s'al' (if the temnpera~ture fluctuations.
I're-du-ta4' v:.1tivs, otf giner~i-te' noiolsv :ari' rmp~ared to mt:,sur'il .11*3i) low fre'cuvn'.%Irolsv4. M1td,4IT4'( v'3I4M s of thet vtarlotas turbine stage veioitatite. anti pres~sure dtrolpsWil4 IeI irnputtii1 144gothilr .vith Owhe rnis ti-nipu'r~iura' fluetuations :and the tehairmte'rist ie'vngI h sfualvs oif t he hot spots tobtaini-da fromil vroms-rorrviatitin of a41jm-t-flt aiuivk-
4.4 U')[5£ tli'nai). Itp~'4). 'v-'.li tvid po)wer li.'vc' oiEf noise wur foun to h4i.i4 e in goodt* i .'geiawnt with 14i4:-:;4444 dioI&;i . . -~a' tli di*41i4t't .:IiIr1 ':r,' : ,jIi 1 f
tht(. axial hot-Sp'etleit !v-a~e4 andM :itxia:s l convt'c'tlon ve4st4,4itv, pe ik at -100 WI a4s dot4W
HI$(-I.4'1U4- lilt pro-i'4'411jt' and Ij1 4 :.nurvt~il flois 4l'V#1 :ivli re in rea;son~able lagraeem, ntt,it !s dediuredi that ('Prt, engine- noiv(I'tgII Im' avrtouzittd for by the temperature~ fluct-tta-tioual convecting through the turbine'.
~.- ,;a.i.:i ! ;.-.,,n .. . \It ii •imiLiar l':y' I,, ;.
"}. ;)t.-bi litv that a tim:w :tr•'ing temperature were traveling through a velocity.n...f:-t. :isanuther :..)urv-. of sound (entropy noisej has received little attention in the:'!o'ratura*. Sfrahl,"' ,i,' cusselI entroi)r noise, hut made no evaluation of its contribu-
*n to tJr,, tengin, noise. St've.'. ricl-v.t theoretical approaches 3 0, 31 have studied• i•. gene ration b%" convection of "hot spots" through a mean pressure gradient. The
.i:.s hy l'ic-kt-tt ctonsider.. both vorticity and entropy fluctuations. The applicationo i,,,.kett's anal\ sis is perhap:. th,. first attempt to quantify the entropy noise. Pre-* :k•- spectra :and power |e~t'l, from measured parameters compare well with mes--:r.'t.! Iata, in,rlit'ating another noise source to be included in core engine noise pre-,i,-i on prowcedures. No attempt has been madtt to establish the level of entropy noise, ,-i-tive to I he. mort gtlv rallv acce'pted direct buraer noise from the combustion
E'l-,uation of Paper
Thi.g paper presents an analysis and mean, of predicting the level and spectra of.ntrop% noise in the c'ore engine. However it is unlikely that the procedure can soon
he integrated as a separate component source in usable prediction methods. The com-phvx input parameters requi rted to evaluate 'he entropy noise are not generally avail-abh. and results have not been demonstrated to be.universally applicable.
I",)
* I ., .h. .:ncJ Ilikhinbr~and, it. W. "Re( -tion of* f*. -irsm~~~ l... . .. : i-: s A , AA Paper No. 74-59, Presented at
:.ýX!;~IiaA .. - .~' tr~ !ainuarv 197-1.
la~ i. ~,.,rt - .*a 14i. 01- sc .. : . ribied in.ul'tail in A~ir Force Aero.q.!1it a,.,~, va k~ ia I) i.a P- rI -7::v-7'Y'. 11-ý oi:Vctive of the
!hi ~..- dtw s -lrt]. ia.at !J I!~. tt'i~lt' I.asc neee-s:;ar-v !o reduce the n~oise signa-tuft, w.; -'. 11' all III.,Yr' :knaa I., plot.ai en.-int s to min imizie their uletectabilitv in low
~a ii uIr .* i.n;:a ~~ur~'iil~ oa n ili iarv is;issons. The program summxa rizedw:.- aaithtr tris :ir..d ~if( livio.1i d-' %c.f'lripi t i t 4 pridfiction methods for all the-
~ .ju * S a1Wa I tual .j -Fop at" ri-10.1 .1 ftj aw! Lu rILo? to. va;ine..s 2 developinento i
luL't :ciuustlc trt;Iltfl-11t dv-IIE.ln 3 :m t!'4ts of xviaternuts suitable for acousticduut linvirs. -it acousti ti sts tI :ait ur uppres-led turbofan (the AiResearch TFF. 731-2):ind an unnu1 11 ,rvs-wd I tarh'iprop vni~sin (the Ai~est-arch TI-E 331-5-251) including corn-pat 11 4Mn V. ith 3acra(it to-d 7)~t ~, 'a. uu.%it tct:M (,I vairious inlet mufflers and exhaustduct treaztint-nt, andth,; an ;anal. s:.s of performan.ce and wt-ight penalties for noise~upprussionf. 'Ilh4 .w'rk 0.1 Lurb1.-.haft engines a iid their suppression is of interest Inlit-laaa-pter nohise' pred'ictiona anda will lit alasvissf-d below.
[';-if ii~d compir4s-vir i.'ta p redic~tion .nithexts are based nn work- reported by Smithandi House" ' with erio.!it icatpi'rttit ini prov( correlatlion with turboprop engine data anoall'ow prudic;itiona of e-int rittigAl compressor noise.
let noise abovte 1000 It. /s,.c. exhaust velocities is pre-Aleted by the SAE~ jet noise
-I 1* 011l 1,11P .'iapiI 1ia IretvtIvitv c~ut vi-. At exhaust velocities titlow 1000 ft. 4/5cc.thipaper st~ate's that prvdioiti ian' are based! on Isushehl's method:1 . In this exhaustve.loemt region, the nua'ie i.s g- 1iteraited Intern~al to the engine anti is called core engine11011.0. 'The onl% curt, engine' noise source' predicted explicitly in the paper Is combus-for no!,,%-. It i,4 statlid t?..at e'ornlueistion rs fliSs ime of the most significant core enginenoise' source's for small turbulan and turboprop emgnilas. The combustion noise IsjpredhictI'( 11) Ix- a feim tion of teit4'r:Iture risie in the combustor. combustor dischnrgeve'locity, c'onihiixtor gli~mm'ter, NOe' and air weight flow, and a reference acoustical
aYV~l outputf ;i! thev r-umblus;c;r ex~it.
Sina' :a -a;'.variox I-, 1te' 1Uirofei It) providvlIN loripw -r1 ~ t Inv pmiopvr rp'im to driv' apropea'ller ofI~* rototir,,h I hipe)j)r cons iaIe'r:i gvarbox nt.it!~ ;is pairt of the e'nginp. The
tat!- a s 'i-1 v) U f Ili-- in' t oac en'f li.hia App-nij)'1x for a ulhousvii.don of the gearnoiie' prtediction met hol! th-sirtxs!d.
V-1,1i: r 11.epnsa -:111~sisc, sicUh :1--i fuu: I i:.d lubri'-ation pumps mounted on the1* ;1,t Of Ill, *-n::t-il, ;1!1,.'i itcres !:i or ~*.r 'v quliet systems such as reconnais-
. * Su. .t* 11. lidto. pr.qi pI I- is -I htc In.11:4. :!t-,- probdaby unimiportaint ansi a i fa-
.*].-V The~ ps:per states that verv. little work1 -$ -I£?l t (:I Ot4.' l u , ..t it dot'-! inclcudelt a preidiction i Ilt-hISI for a fuel
.s. w~, 1-i--c is tliat wthiich is transnimttt-d to the far fivld thi-ough the walls sur--a6-, ina, fit h.- jiginit, v03inrU-int-a. Iii L-mpiricaZl prcedi-tion prucedure fur sound power
:. .avIi.- pr.-i-nsi-uit- for turboprop engincs which is a funetiori of mechanical horse-i eteates ha. the ctigine.
I Ihrt - .tdJ-oit u durt Lining ii'-. ign prntss-t-du re-~-ar, de-scribed bra.:!ly in the re-Poirt with i'i-t.atter information :ivailable in 'A lAII'L-Ti-7:i-79. TIhe tirst method
1,t-tAon thu woirk tit (i-:-fl1:1 andi Nelson is -an~al-tical in nature, Iit, uses .-in tempiricalianp-iied-s- rnioiel for iiiateri~als used in the linor design. The sec~ondI method Is onlyii-wtitint-ti brztaiv :sand it is stated that it is a self-optimizing method based on simul-
flitou."sol(.utionl uf the governinig diffterential equations and that it avoided some of the* aimplif-in.4 assumrptions of the first method. A single comparison of a liner design* ais .ri-sent.-d %hiuh show., that thet two) methods give significantly different results.
Thl.- diri rtimt-thodi is empirical and is hase-a tin gene-ralization of the results of manyic - -.t of due-t Iine r vorifigur~at ions.
(;-nvrxal ri-s-uits of aicoustic mal~terial.,; tests :ire presented for zero flow, roomt.-ivap'-V-tur- voiwijtjons. S~ianplae results of interest are: 1i alddition of acousticAi-a;urhimng m~aterials behind pierforated face sheets increases absorption coefficient
WAl ac-oustic res4istance, 2) little is gained in using sound absorbing material behind* ~iii-t rinctat since( air cavities tuned to the design frequency providle significant noise
* *~iI*.a fl:ikof onver sv'vra-il octaves band-, :1) bulk, absorbers show onlM a slight frequencydriri n-11nce on matatrial thickness and absorb soumd across a wide range of freciliencles. - -
AcoL.ttae tests oif ann Ailb-search TPE :131-5-251, 8-1 0 811l) turboprop engine werevow.ruute-a while: the- engine was drivinig a qIuiet udynamometer. llnsuppressed tests.x. re- ( miuc-tell to establi sh c'onipa risons between predictedt and measured noise!,preCtra. Fit! repjort indicates that gomid correlation was :'chieve'd. The engine wnsthvi; t. sttd with mioltil~ar hila-t, casing andi vxiaus t -stpression .syatemns as shown inthl.- igu ri- fli tilt- Ie-xt pa e
Cashnj, stippression rv-nulls are not indiicate-d in the report. Inle~t suppressor tes 'toshanwtal splittrrs in la rge or .4mall inlet duct sections pro0vided~ little additional attenua-tion, but marked by increased performance lossesH. Therefore, the best inlet suppres-mor consisted of a relatively mimple large plenum designed with no direct line of sightt-anoirninasion path.-
104
* .. ::r:.I'.(onmti
*... a ! l
*1 ~ ~ Il IN,.
EXPLODED VIEW OF ATTENUATION ASSEMBLIESUSED WITH THE TPE331 ENGINE
1h'I Ie xhau'j,t ;atte'nuaitor t-')nee'-p* sch-ftedt4( for the ti'sting reported utilize- twop.*inuip il t-c hn',juvii to reffid~t elow frIMquonv-, fani?;i'': 1) a~ length of tailpipe' which will,,hilt t thi Iiin'Ia ntentai i *',ori.snvo if the. taillpip4 !'j a fruqluency where Ilu' ambuient akground nok"v is higher -int tho-ri-lore iamlIIk- the entgIne' noiw inui 21) a1 niultj-tube dlst.4gnto, vonvirt low fr'riuo*ni'v noitiv i:irgi' wavive~ngth.sl to high frt-futrncv noise (smallwavi-hingth.4i which cien reqae~ilIx- a~*;la~iorheel. Twevr%( v.chau.9t duct conf igurations were
te:t..I)f j'ir rler sg in-J`1,:auwv Wi' w Ito he' t'i which --howced thatL dIuuiing th~e lengt h'if tIitrc~liviuI'.i P I...d'-tl .ihr TheO:':) i riii ~IC4 In feimnd Iy t;ti-.*r rp--arct-t-r4.W~Yith 016 0111`1e wutInr ~**4ei'l'v Ieinm, nn',r. I h:in 30o cil redurtion was~ obltained in theInIvt yju:eidrant atI frolil'nenu )1:e 1(i I 00 Iii. andI ;e've'. In 11w' exhaust qIuaudrant. aittenu~a-tion of mort! than L') dil ait I! riliut~i i fI10)I, n hoewe ei'i
rho final Item mI'tret'ssi'i n the patwr lIs the vi fect of inlet and( exhaust muppremsionequipment on perfoa-mavice ;andi woi.ght. Am i'xpec'ted, livi trendsx prrse'-nted sthow sup-
pri-mmor duct weight rising raplidly as frequiency of sup~pressor peak attenuation filli1w low 100)0 liz. 'ibl:4 I.s 'hue lo th requrv I4(U 1.1ei 'p1h (1 hltknvami of the t re'atnient. Thi
_____iunti
* . ..- ' r * zt.tri.I.:- ~is~tz~ti %ith various vxhau:ýt ducts is compared with calcu-* .~t~ ~.rnt*isaigrct-riknt betwee~n valtul~itlon ;ir.d test is indicated. A maximum ofIons in h.j1*C4U11 *.Iotra tht. full bwid high flow coflditiun is infl(i:td.-J
i iýnWith Similatr PaperIs
I hit:- pierisak drrv v** frijh a six volufht- r-port v.atIe "Suiall Turbi ne Engine.%i, M{-duclion, *Air Forcu liepurt AFAP l.-'TH-73-71-i which was writtern 1w
i ,*r..l auth~irs from Aiuv .war; h Mainufacturinig Company in V)73. Also, a paperti.,L d 'Pro.gres.s in the De.~vlopinvnt of Optimally Qjuiet 'rur&Aoprop Engines and Iiistal-Liti-jmn< SAF Ilipr 7312i-,~, A~pril 1973, by ft. %I. 'Vedrick and It. W. 1H11denbrand was;,rr*r veel from the six volutne report.. 'rht Shah.iilv, et al p~aper is :i very grGtM sumn -
!:I~la*-, .:) tht- work reportrid in AFAI'I.-TI-713-79. While AIFAJ'L-Til-73-79 inclludesti4. e'mp~tAr prIograins dltvulopcil to predlict engine noise and design. duct treatmentin :i~fifit ion to :t grea.ter emnphaIsis on turoofan noise, the Shiahaiiy, vt al paper provides aln:tter ovvrview of the arceomplishnients of tOw program reported in AF-APL-Tlt-73-79.(fllwr retports emtphasizing acoustic testing and dlevelopmtent of prediction methods fors,un;sll turh',shaft engines (do not exisi. The recent work by General Electric under
l,1 I- -kA ('unt r.ct No. 'r'FA72W'A-30:!31'1 does include inivestigation of similar:souri ves in great expeirimental depth, but the emphasis Ia on understanding turboan-c.rvr engine nloise of larger vnginec:.
F>.-alu:it ion of .Paper
This is a veryv valuabie summary of theŽ six volume AFAPL report for a researcher.6-*neral trends in turtx)sh:Ift engine noise will not be found. Also actual calculationscannot be dlone with the limited Information reported'. These require use of AFAPL-
", .irvk, It. N. an -:;;I1!t:nitjrand, It. %k , "!Progre.is In the Di:velpmert of cptim.,Iiy•':v.t i :•rto)pr,,p I.n t-.,-s .x,',,Iil.t:.lathn' S:\-F P'aper No. 7312.s7, Pret-..ie•td at the
I hi-.. rqpwrt :urmni:ari7r,. the turhoshaft enrgin, noise evaluation work reported atA .At,.r ,i.4t, in rbor,. ui,.t.ii in Aiir Forre A,'ro Propulsion Laboratory Tectjc.,d He-
:prt A FA Pi.-T1-7:3 -7!. 1 h,. purpose uf the paper was to summarize the turboshaftvngie 1af:)raIn pri,,r" i, lo rcht;i uf thet final Acro Propulsion Lboratury Report
in ;. way theft would h,. us,.ful to m:nufac.turers of business aircraft.
Sunrnmarv
"I he following surnnirv i.% ihnited in scope as more Information wll be found IntI" AL:A p):Il-,.r I)v Sh:ahai,,.l ;412 7 or the Aero Propulion Laboratory Report 5 which:ir,. rteview,.l el t.I,-w ' rv in thi. Apl nlx.
Co'mn~paerison With "irnil:ar Il'prs
This p.aper is linited in s(.oixp compared with the AIAA paper by Shahady, et al.AlHo the predi(tion procclurt.. for engine noise and duct liner design which are foundin AFAI'I.-TiR.-73-79 are skot Included in this paper.
l- valazat inn of lil'p r
It is suu'ggested Mhat the reader Int,,rested in the numinary ot the results of theSma!l T'urbline E~ngine Noise Rteduction contract conducted by Alresear h Manufacturing('Comrpanv for the. Air Force Acro Propulsion Laboratory refer to the AIA• paper bySha:dyv, et al or the ..xrutive Summary, Volume I, of AFAPM.-TR-73-791 as both of
these reports are m.,re complete than the report reviewed ht.re.
[hi,'n G. V.. "Noisu From l)iesel Engines", lnter-Noi.:e 73, August 1973.
This p~t-t'r discusses som. results of experimental vibration and noise measure-mcnts on diesel engines. Vibration isolation of external engine parts, stiffening, and::".uiud rIducing sh:-_0s are shown to be effective means of reducing noise.
In nearly all modern diesel combustion systems the combustion pressure Is the-trongest exciting force for structure - borne and radiated noise. Noise reduction byimproverient in mechanical exitation sources is limited to 2-t dB(A) for technical ande,'onomic reasons. It is necessary to improve the structure so that less vibrationtCeliahcs the outer walls to be radiated as noise.
All parts of the external engine surface contribute to the external noise. Seldom,does one pai L contribute as much as half the noise. Nearly all parts must be treatedt. &Lchieve improvement of 4 to 5 dB(A).
Noise near the oil pan can be reduced by aq much as 11 dB(A) by careful isolation.Stiffeaing of external wall can.reduce local levels of noise by as much as 10 dBrA) In-.ingle third octave bands. The most effective means of noise reduction are thin soundreducing shells of low bending resistance and high critical frequency. Reductions of19 dB(A) were measured with plain sheet steel and it was found that mounting is morei..portant than damping. Sound absorbent material in the clearance between shell andCLSe wall had little effect. Measured levels of engine noise were reduced 19 to 21"JB(A) using a total enclosure with vibration isolat'ng attachments.
The best design solution for reducing noise appears to be a new design withcentral support engine structure surrounded by a vibration isolated housing, "whichiorms a kind of wet enclosure".
iEvaluation of Paper
"this may be of interest in predicting the case radiated noise reduction which canbei achieved with relatively simple enclosures. No means of predicting sources noiselevels are contained in this report.
108
(ct r Noi•e Ca:ipsule Sta.arifes
l___,ly, it. if. and .1;it'nu.n__.M., , "(4-arbox Noise Reduction: Pred.iction and Mea-sure mtnt of Mceah-!.rcquh c.( - Vibrations Within in Operating Helicopter Rotor Drive
e.. T'!•", \.AS;., i:pt.r No. 73-DET'-31, St-ptemher 1973.
The purpose of this study wis to verify the accuracy of anal'-1ial methods for* predicting the vibration and noise generation of gearboxes by determining correlation
between prcilicted and measured data.
S~Summary
rITis stud% %ka perforrmed on a CII .17 main rot..w drive gearbox. However, the
* analvsib is applicable to gearboxes of all kinds. The paper presents a rood descrip-tion of the seve ral analyses required to make the prediction of total noise and vibra-tion emi,.sion at gear clash frequencies. Also, the correlation between predicted andnmeasured responso of :,evera! parts of the dynamic gearing system is presented. Thelist of reference~s covers the work sponsored by USAA.MRDL over the past few yearsin developing analysis and noise reduction techniques for transmission noise.
Comparison With Similar Papers
This is an extension of the work perfor'r:ed by Badgley and Laskin3 , Laskin, et all,
and Sternfeld, et a05 .
Evaluation of Paper
This report shows 'hqt an application of detailed dynamic analysis to a transmis-sion can identify near resonant condit'ons for components. This study shows examplesof this and also shows the results of corrective measures which yielded noise andvibration rAduction. The anal),is Is 'eiigthy, but necessary to locate possible vibra-tion/noise problems in the-preha,.dware stage. It considers dynamic system torsionand bendir.g plus casing response.
109L
B:,l•'iiy, RIý., and l.askin, I., "Progiram for !elicopter Gearbox Noise Pretiction
aniil itedUuction', UISAAV1.ABS Technical Report 70-12, March 1970.
d'urpose
The work described in this report was done to demonstrate the application ofanalytical tools to the CI1-47 power train to predict noise levels. Actual CII-47 trans-mission noise levels were measured for comparison. C--47 transmission casingvibratory response was measured. The sensitivity of noise level predictions to several
transmission design parameters was determined and investigation of tooth profile modi-fication as a means of attaining reduced transmission noise was explored.
Summary
- This work shows the ability of the previously developed analyses to predictdifferences in transmission noise radiation via modifications to reduce torsionalexcitation and gear tooth dynamic force levels.
Comparison With Similar Papers
This is a follow-on to the work performed by Laskin, et all.
Evaluation of Paper
This a slightly refined analysis compared to that of Reference 1. However, itstill does not treat the lateral beading dynamic response of transmission components.It appears to predict the spectrum shape of noise and vibration, at least to the extentthat some clash levels are higher than others, using torsional vibration of the systemwith some empirical conversions.
110
Barlow, W. If. , M'(lu.y', W.C. and Fcrris, II. W., "O'I-6A Phase II Quiet lleli-copter Progra m", USA:\.1I)RL "rthric'al Report 72-29, September 1972.
Purpo•e
This study was conducted to reduct. detectability of the Ol1-6A Helicopter byreducing externally radiated noise.
Summarv
This report prt-scnts external noise narrow band spectra showing the presence of
main and tall rotor gearbox clash noise for the, version, where this gear noise isnot masked by rotor and engine, nois.. It sh': gearbox noise levels of 59,'55 and.54dl1 at 150 feet In hover for the tail rotor gcirLox, second stage of the main gearbox,and the neces:;ary drive sc. tion of.the inaij g,.arbox, respectively.
Comparison With Similar Papers
-.............. The-werk-descrit rt-wasper��-srpaedffctl• same general effort as thattundertaken by ljo-es 7 .
Evaluation of Paper
This is one of the few repcrts available showing the presence of far-field gearclash noise from a helicopter. Gear nclse was unmasked by reducing rotor and en-gine noise. It provides useful data for estimating far-field radiated gear noise.
#in
Bowe•s, M. A. -Tr"est anid E.valuation of a Quiet Ihelicopter Congiruation l1H-43B",
US.AMIRDIL Technical Report 71-31, January 1972.
Purpose
"rhe purpose of this effort was to reduce detectability of the llH-43B helicopterby reducing externally radiated noise emanating from the main rotors, core engine,and gearboxe.s.
This report presents external noise narrow-band spectra showing the presence ofmain transmission gear clash noise. Levels at 200 feet in 10 foot hover were 74 and64 dB for the input bevel and planetary system clash, respectively. Changes to thetransmission resulted in reductions of 10 and 8 dB for the two clash peaks. Trans-mission noise reduction measures incorporated were: Installation of a selected gearset exhibtt ng good wear patterns and minimum tolerances, plating of the teeth withlead indiu..i, use of high viscosity oil, misphasing of left and right bad rotor drivegerrs, ela.*tomeric isolation of planetary ring gears, removal of some auxiliarycomponents, and partial sound proofing of the transmission.
Comparison With Similar Papers
This work was performed as part of the same general effort as described inBarlow, et a18 and Pegg, et a19 .
Evaluation of Paper
This is one of the few reports available which shows the presence of far-fieldgear clash noise from a helicopter. Gear noise measurement was made possible byreducing noise from other sources (rotors, engine) which normally masks it. It con-tains useful data for estimating far-field radiated gear noise.
112
Grandte, .. , 0l a!, -ai,,A]i i'urhant.I.nginv Noise ltuluction, Volume 11, Noise Predic-M .fithod.-', .r I'i 1 t- At -ro. PrIulsion l.aboratorv Technical Report AFAPL-TR-
.3-79, Volumv 1 J1,.Ot-tlh r i'i7:.
The secttion ,)I concern hr. .Sucti:n 11 - I'irt :, (;ear and Mechanically Radiated
Noisvi revitews the lit'.1lurct iai .,a'i'i.' lioi:. prldi-tion and gt:nerates a basic noisepr(diLteion nithodn via char ts.
Suns mi rv
(.earing. n.1so, pr' di. Con i- i .. W.. -.. r .r' . sJI I",a. , x'itation through meLhanicalradiation. ",'h a ii,., h.vzic iti'ul-., il v. ith ,:.-t .tAion, including unbalance,tooth impact, frit , Ion, and git|,f'.'ting,, arc ti*..-ci it t (I .nd analyzed. It is determinedthat tooth ainpa.t is the dl,,ni..:int inct.h:n:m.-si for ct.re.'i:,li, radiated gear noise whichoccurs at meshing tr',u-nc'.
Tooth impaict ,(,i.itif'n i. causcit lov initptiect meshing of involute gear teeth.This imperfect mneshin,-, i-' vau.vti by ilinh( urait.s in both tooth spacing and profile,by deflections of the It ,.th ca.'u.. ,v hloads, :and by movement of the pitch circles ofthe gears (lue to sh:ift, It.:,imn.-, anjd a-iing deflection.
Tooth impact 'au-e', tMesh ft..'tutV1.v vibration to be introduced into the system.This vibration is tran.m.,itted niechnrical1v through the system to points where It isdissipated through fla;,apiug or :av ousti. radiation.
The dt-tails of tocth impact excitattion are discussed and dependence on operating,design, an(' qualit% tujtrol p.ardia',ttrs are identified.
A prediction niiethxiA is oleriAi to arccot'nt for as than%" of the pertinent excitation,transmission, :and radiatran :iranic'ttrs ai-tre identifiei in the cited literature. TheseInclude, in part, power transmitted, tooth loading, pitch line velocity, tooth profileerrcrr, tooth profile roughro.s.4, tooth spacing error, tooth alignmeat error, pitch,contact ratio ,,pproa:-.h ,,d recess angle, pressure angle, helix angle, tcoth facewidth, backlash, phasing, housi.¢g responise, bearing type, Installation and lubrication.
The authors concludel that "the wide va;'iatlon in gear system construction makesaccurate prediction (if the g'.ar rnoise s.ct.run -in impossible task, at least with thepresent level of knowh.ig, of gaa.tr L. isa generation and radiation." It appe.irs that theest. ;available mwthods uor gua:r noise predliction constitute only a rough cut at the final
Spe•'ctrum. It is cv:aimedl that t ht-levls of the dominant meshing frequencies can be
,prt..ietttd within (' IlI which is hil.,"4 I Iuc.-t ion:.l; Ie le:.sed on tho know;n variatitty ofcasing and related -tUrfaiveI r:adi:atlon properties.
113
C(omparison With Similar Papers
This report teviews the detailed gearing noise prediction methods of References1, 2, 3, 4, 5 and others and concludes that they are of limited usefulness.
Evaluation of Paper
This is an excellert summary of gearing noise prediction methods including thosethat require eonsiderable detailed knowledge of the transmission design and those• %hich are more practical anti more easily used. The prediction method proposed isapplicable to a uide range of gearing types, sizes and quality. Helicopter transmis-sions occupy only a small portion of the range of variables covered.
114
~,o
liartman, R. and Badgley, R., "Model 301 lILHATC Transmlssion Noise ReductionProgram", USAAV.-ABS Technical Report (Contract DAAJO1-C-O0j-0), January 1573.
Purpose
This study was conducted to reduce Heavy Lift Helicopter transmission noise byidentifying problem areas analytically and making design changes to .reduce clashi'rt-quency vibration and noise.
Summary
Dynamic testing %as perfornmed on a GH-47C helicopter transmission with inter-nal Instrumentation to nmatsure stra1,9, aeecC!eratlons, and displacements of rotatingcomponents, and external instrumentation to measure case acceleration and noise.Test results were used to v, rify prediction methodology which, in turn, was used toanalyze the dynamic response of the HLH transmission components.
Comparison With Similar Papers
This is a follow-on to work reported by Laskin, et all, Badgley and Hartman2 ,and Badgley and Laskin3 o
Evaluation of Paper
This xeport provides some of the most detailed analysis of transmission clash fre-quency dynamics to-date. iHcowever, details of tLe computation methods used for sys-term coupling (except for torsional) ard casing response are not Included,. R providesgood tracking of the flow of clash frequency energy from the source to ultimate pointsof radiation.
115
L.skin, 1., O-cutt, F". K. :Land Shipley, E. E., "Analysis of Noise Generated by UH-1iHLlicopter Transmission", USAAVLABS Techrdcal Report 68-41, June 1968.
lhe purposv was to dev.lop effective technology for the computation of helicopter",,.:..box operating noise and to apply the derived technology to an analysis and evalua-ti:.n of the [:1I-1 helicopter inain transmission.
In this report, tv(o basic programs which were developed for the prediction of
gearbox noise at clash frequene.es are described. The first program consists of atorsional (liolzer) analysis of the system taking the compliance of mating gears intoacco unt. The second program determines the excitation introduced into the systemat the various meshing points based on the geometry of the system, including thevarious types of error occuring in aircraft quality gears. Noise is determined em-pirically, equating clash frequency torque oscillations with noise generated.
Comparison With Similar Papers
This study forms the basis for the analysis of gearbox noise carried out in sev-eral follow-on programs including those reported by Badgley and Hartman2 , Badgleyand Laskind, and Sternield, et a15 .
Evaluation of Pa'per
The work required to predict transmission noise ia prohibitive, considering thepoor results attained in forecasting absolute levels. However, the technique. If Itcan be made to work, is helpful in td ntifying possible torsional resonances at up toclash frequr.cics. The comnphete lack of consideration of lateralbending of compo-nerts and dynanle component mounting lmpdances eliminates one very importantpart of the overvll problem from any consideration.
116
P- ... J.i lfLi-tndrsun, ii. It. and HfiltoD, I. A., "'Results of the Flight N'olse
Mt :.nur•tm,_lIt Program Using A St: ndarrd and Modificd SiI-3A lelieopter", NASAI ch:•t-cal Note D-7;33j, Ik.•'vibt.r 1t73.
"1 his Technical Note reports the noise characteristics of a standard Sii-3A hell-copter and a version mudified for lowt-r noise generation.
Summary
This rcport presents hover external noise narrow band spectra E: -.- ir-g tall rotorgi ,ox nfolbe, level ,f 55 dB at 750 liz and at a lateral distance, of -.. If-ot r d 270Idegrees azimuth at Lu foont hover. Power to the gearbox is approximately "00 horse-power at this condition.
Cami -sonf ithS! m,!ate-Lra-- __
This work was performed as part of the same general effort as reported In Refer-en.es I and 8.
Evaluation o)f Paper
This report contains far-field test rotor gearbox noise useful for estimating pur-poses.
117
Scilgl, It. G. and Mard, K. (G., "Transmission Noise Control - Approaches tnHt livoptcr ASiNn", ASME l'apt:r tJ7-i E-5s, May 1967.
Pu rp ise
This effort kas condlucted to define a number of methods which may be em-pluyued to rteduce the level ,of (.lash frequency noise generated by transmissions.
Su niim ry
This rcplyrt provides design criteria for severaw schemes proven to be useful Inretducing transmission noise emission In helicopter and other tranrmissions. Tables(it icribe the degree of noise reduction available through the employment of each of
thestt nia.;ures.
C'niparison With Similar Papers
This reV)rt covers a broad spectrum of possible gear noise reduction measurau ,some of which are treated in more detail in other reports.
Evaluation of Paper
General guidelines are presented for low noise gear design. The only apecifictectinique detailed is that of ph.asing planetary system gear clash for cancellation Inthe ring and sun gears.
118
Ii , h..ai --r J. It. " 'An lnvi-stigation 4 fit.'l i pler Tranas----,) I' !1eii'il,.n by Vil,riatl*-ri AYh'jz'lers :andl Dmping", UAýAMPi)I. Tt'c.h-
'I tI purp' ,Mt' of thi s tu&.' A :s !4. fit triw.'zaa: tht. trlinsmission noi '-v reduc'tion po-i:tv.:l d .)I y iI.jn( Lt'ar vilbr:titio a.ahoitrb.' and gcar damping by tes~ting in a helicopter
.',*t'I'.ILJ till1:; .1tt.iain'd %kert :is .i'gli :as -s 111 f'jr some of t~.t siiacrnes te,;tted.if~ r tht'. -:ex''uctj DIIs %%v- I. .ca: in earl'. y all cases, resulting in little or no
ch.amegs' in flt-e t'tal now:e :andE vibration output )f the transmission sy-Aern. Further.41idur!Ii't var't:llc' f-jr to idt-ntify the reasons for this result in termsb vf casing
.:e awrit-ri With Sinidar Papt rs
"I Ill.- iS M-1 ;Ar)piieatior .#f the' gcar n'ilst' analysis techniques of Refer-ences 1 and 3t-) rtiluc'tion of cl-is MItI eliJ''ncy andl not ýe.
Tito-' ri-poil iI shoA, INAt somt! naoise i'aluc'tlans are attainable %da unergy absorbing~yi'a. .lloweva'r, tlit relatively small reductions achived Indicateta h oa
flynamic systi-m biehavior must be better understood If significant reductions in netnuis.' rnalditio~n are' to) be ac'hieved via the technIques evaluated.
1 191120
:jUbjective Reaction Capsule Stu-ries
AtdcOck, B. D. and Ollerhead, J. B., "Effective Perceived Noise Level Evaluated forST. 4. and Oth,..r Aircraft Sounds", FAA-.NO-70-5, May 1970.
Pui •S
Tht- author's intention was to determine the ability of the Effective PerceivedNoiise Level (EPNL) and other scales to predict the reponses of subjects to the soundsuf a variety if aircraft, including those powered by turbofan, turbojet, piston and tur-boprop propulsion systems.
Summary
Testing indicated that the differences between the various ratiig scales are typi-cally( of the same order as the experimental error incurred in performing the tests.It Is sIuggcsted that future ,fiort be directed to explaining the deficiencies of the vari-uus rating systems which cause them to yield substantial differences between theratud aid judged noisiness of the various classes of Arcraft.
Comparison With Similar Palpers
The conclusions generally agree with others (e.g., References 1, 2, 5, 6 and 11)that dBA is a rea.wonable compromise unit for quantifying helicopter noise annoyance.
Evaluation of Paper
The most significant result from this study is that all of the rating schemestested attained similar standard deviations about their regression lines, indicatingsimilar accuracy for forecasting the subjective annoyance-of the S'TOL and CTOLsounds tested. The rating scales evaluated were: PNL, PNLT, LL(S), LL(Z),SPL(A),-SPL(Bi), SPL(C), SPL(V)), and CASPL. Ihence, for turbofan, turbojet, andptopelter driven SFOL aircraft, any of the above ratings is equaUly goad .(or- bad) atpredicting subjective reaction from the community.
.v.~:.::.U~,1Ij~I't trit~.rr~cie14a Ntise Inicluding Implications of ldentiffyIna
*±2At M AV'u ~lfu~u.ai lct sure', Erivirounmintal Prutection
I Le~ J)urhE)51 of this n(As,ie study was to determine the merits and shortcomings .af.:.t~.'k thueiacti-tri/i. ti.v Impact of noise of present or proposed alrport.'aircraft
*Iiqtr:it41sn:. on the public IVealth itnd welfare, determine which ineth-id is most buitable.. ar:e!'';~I)%'.? thfe. LX 1tdvrA1 (uivernment, and detcrmine the implications oIf issuing
n . ' -ifriUlairi-.im I~th~hn a standlard method for characterizing the noise from.itircr:la~ iirport 11).qwi'ti'ur.S MAn~ Of specifying maximum permissible levels fur the pro-
Itei.-4 0". pbic61t Lvalth :aii1 -'l efare.
This report propoxses the use of LdIn for the objective evaWh;t.UA of enztnpmntsl -
tjolst.. it rectillfleflls a, level of L( fl 60 as realistic and acceptable for control ofhea~ring luss, spetech communication, annoyance and general health. It recomitends
(J~ai~ Vic thellowable level bjy from 2 to 5 dli for environments where pure tonesart- kiv'c.tn to he. pri-strt. The constituents Of Li~n are -given, including a single event1jurameter called Soaa)Lnd lExposurc Level which is ap~plicable to a single aircraft pas-
This dlorument forms a strong, wedl supported case for the use of the recoin-mi-nded comnrunity noise criteria. It forms the basis for the studies reported by1linterkejs.er and Sternfed' 0 and Munch and King"1 whicb wcre aimed specifically-4t the- helicopter application.
Evaluation o~f aqr
Ii ei': "-rt forun4 m av exciflnt catie for theo adoption of JLdn 60 as the ultimate;f,pal hor the nois'e environment. hlowfiver, it does riot take fully Into account thervalitics of the current noise environment Where this limit Is commonly exceeded andwhvrs- Its Impti~tion would he Ymeaninglems and would Impose severe Ilimitations 4nmany scgments of the ljusinef-H community. It acknowledges that, the proposed goalA1al.11ld 1w :'I1)Jle'ct to a. rhe'l'Ae for Imjlementation but does not detail such aL schiedule
122
ICox, C. R., ."Ieilcopter Noise Reduction and its Effects on Operationse , Paper No352, Proce~ihngs - 25th American Helic_.ter Societ Forum. Ma- 1c969Purpose
" To present the factors that influence the reduction of helicopter noise and discet
their effect on helicopter design and operation.
Summary
This paper compares helicopter noise with other types of environmental noise,indicates that certain flight conditions are associated with above-normal levels ofnoise generation by certain types of rotors, and presents trends of the variation ofrotor noise with several operating and design parameters.
Comparison With Similar Papers
Noise parametric trends presented agree generally with those of the remainderthe literature. Flight conditions generating higher than average noise levels arecovered in more detail in Reference 15.
Evaluation of Paper
This paper uses only Perceived Noise Level as an Indicator of h~elicopter annoy-ance and deals only with the 3 0 0 0-pound, two-bladed, single-rotor helicopter.
123
£dge, P. M., Chambers, R. M. and Hubbard, H. H., "Evaluation of Measures ofAircrat. Noise", Proceedings of NASA Aircraft Safety and Operating Problems Con-ference, NASA SP-270, Volume 1, 1971.
Purpose
This report discusses the status of development of measurement units to properlyrepresent human responses to aircraft noise.
Summary
This paper identifies various ways in which aircraft noise affects people inculingannoyance, speech interference, etc. It summarizes subjective testing procedures,-types of rating units, peak versus effective measures of noise impact, and referenoesthe relevant studies performed up to the date of ihe report.
Commparisnn With Similar Papers
None.
Evaluation of Paper
This is a suLnmary of the state of the art in messurmest of htumm respmas tonoise in 1971. Quantitative data is not presented.
1
/¶
bi I
'I
124
Fidt 11, S. arnd Pearsons, K. S., "Study of the Audibility of inpulsive Sounds", NASACR-159.i, Ma'v 1970.
This study was conducted to perform experiments to investigate the. effect ofphase, duration, intersignal interval, repetition, and frequency on the perceived
noisiness of impulsive signals.
Summary
Six experiments were performed in an anechoic chamber to investigate the effectsof ph.ysical parameters on impu!sive noise subjective noisiness. Five transient wave-
forms (not repetitive) were used for testing. It was found that: the phase spectrum of
an impulsive signal is irrelevant in establishing its perceived noisiness, the ear'ssensitivity to noisiness of impulsive signals resembles an energy summation processfor which no specific time constant was found, and tlte common coirection contours(such as dBA, dBN, and PNL) may undercorrect in the low frequency regions.
Evaluation of Paper
The work presented is not necessarily applicable to repetitive impulsive noisesuch as that from a helicopter. The psychoacoustic consequences of these results,
which were performed for single transient impulse noises, are not substantiated forrepetitive impulses.
125
labAe., D. R., "Fliht 2perations to Minnirize Noise", Vertififte (Ameriean Hell-conoer S•ociety), February 1971.
pu rpso
To determine thu flight conditions which c~ause high noise levels in a metimmtransport helicopter.
Sum~mary
A Beli 205 class helicopter was flown through an extesiw feW pagm Wltify the flight re,-tmes whic& generated blade slap noise. These regtze are presentedin the form of an area to be avoided on a plot of airspeed versus rate of climb or rateof descent. There were four categories of blade slap Identified: IntermitteM slogh
c-ntinuous slap, I',ud slap, and maximum slap. It was found that the areas gomeratimgthe higher blade slap levels can be avoided by making pilots aware of thm awMl alter-ing their flight tachniqLes uppropriately. Reductions of Perceived Noise Level oa theorder of 10 PNdB were attained by using the modified fligM profile.
Comparison With Similar Papers
This paper aupplements the work on trajectory effects in wUch may be 0MA ioReterencea 9. 10, 11, 13 and 14.
Evaluation of Paper
This paper provides a clear indication of the impo•rtc ot blads p "I dad.nating helicopter noir. levels when it occurs. Biwc PlL was used to evalhsatg doe
i elative annoyance of the helicopter with and without blade siap the salami )jsevsdifference to observers is probably much greater than the mseaared frhremos I&-dicates.
126
i1eck-or, N1. It. L. anti Kryter, K. 1)., "Comparisons Betw.veen Subjective Ratings ofAircraft Noise and Various Subjective Measures", FAA NO-6h-33, April 1968.
Purpose
This study was undertaken to evaluate various estiblished and proposed objectivemethods of measuring aircrai .noise relative to their ability to predict subjectiveratings vf the ace!ptability of noise produced by present-day commercial aricraft.
Summary
Paired comparison tests were performed using tape recorded flyovers of severaltypes of aircraft during take-off and landing operations. Objective measures werecomputed for the level of each sound and for a comparison (reference) sound for eachaircraft operation. The relative accuracy with which the objective measures pre-dicted the subjective ratings was expressed in terms of the variance in the computedvalues of each objective measure. The smallest variance was associated with ameasure that takes into account the spectral properties of a given flyover for its en-tire duration and also the presence of pure tones or other narrow-band energy con-centrations.
Comparison With Similar Papers
The data suggests that A-weighted SPL is a practical compromise to rate air-craft noise annoyance. The results presented herein are consistent with those ofPearsons 1 , Sternfeld, ct a15 , Ollerhead6 , Adcock7 , and Munch and King1 1 .
Evaluation of Paper
The paper .indicates that, for maximum or peak values, a weighted Sound Pres-sure Level (SPL) is as good or better than the Perceived Noise Level (PNL), whichrequires a calculation rather than simply a direct readout. A tone correction seemsto improve correlation as does a duration correction (an integrated duration correc-tion is preferable). It appears that the use of a tone correction w1th diminishedweighting below 500 Hz and an integrated duration correction applied to any one ofseveral basic human hearing response weighting functions results in a relativelyaccurate objective noise rating scale. Attempts to "fine tune" a rating scale fromthis list of requirements seem to constantly run into the law of diminishing returnsin terms of reduced standard deviation between objective and subjective measure-ments of noise. Impulsive noise is not treated at all here nor is any low frequencyhelicopter type'rotational noise.
127
l1int,,rkeu.ier, E. G. and S'trnlf.lI, If., "Subjective Response to Synthesized Flight
Ntnise oif Several Trpes oif V 1'l 01. Alrcraft", NASA CR-1118, August 1168.
To evaluate subjtctliv response, to the' tur-field noise characteristics of several
types of V "ST(L aircraft sized to carry G;O passengers over a 500 mile range.
Surnmary
The acoustical slgxitures of several V/STOL aircraft were analytically predicted,
and tapt- recordings synthesizing these sounds prepared. Test subjects rated these
sounds on a PNL basis against !et sounds. The various V/STOL configurations are
rated against one another for terminal ann cruise operation with the results varying
for each yp(- of operation.
Comparison With Similar Pape~rs
This paper does not provide as much information on the validity of the various
rating scheme.; as do other references. It rates types of V/STOL aircraft for rela-tive noise generation.
Evaluat•on of Paper
All comparisons were made on the basis of PNL and rated aginst jet noise.
Evaluations were made In an untreated room where the reproduction of low frequencyrotor noise, particularly blade slap, may not be good,
128
ilinterkeuser, E. G. and Sternfeld, H., "Civil Helicopter Noise Assessment Study -
Boeing Vertol Model1 347", NASA CR-132520, May 1974.
Purpose
To forecast the certification and community noise acceptance criteria for heli-copters in the 1975-1985 time period. To determine the noise reductions required onthe Boeing-Vertol 347 helicopter to meet these criteria and the means of achievingthem.
Surnmary
The certification limit recommended is 95 Effective Perceived Noise Level deci-bels (EPNdB) at points located 500 feet to each side of the touchdown/takeoff point and1000 feet from this point directly under the approach and departure flight path. Com-munity acceptance would be measured as Equivalent Noise Level (Leq), based on dBA,with separate limits for day and night operations. Modlidcations required to the model347 helicopter to meet these requirements Include: new blade tips, rotor blade geom-etry modifications, increased fuselage length, and engine silencing.
Comparison With Similar Papers
This is a parallel study to that reported by Munch and Kingal with basic differ-ence only in the recommendation for use of EPNL over dBA in rating basic helicopternoise.
Evaluation of Paper
Tii-ds was a comprehensive study which considered many current systems of ratingaircraft and community noise annoyance. It concludes that the A-weighted soundpressure level provides the best means to denote acceptable community noise by al-lowing the helicopter to generate a time average noise level equal to the noise levelin the community without the helicopter in cases where the community ambient noleis greater than the allowed Leq levels of 60 and 50 for day and night, respectively.
129
SL.,,.rt., .). .,"Wlvi,-• r ,'" Nu)is- - Ar. Existing Methods Adequate for Rating
A..r,.tnct, or l.,)udnls.. *'", .Journ.a of Thli American lielicopter Society, April 1974.
To) est'.llish the validltv of using Perceived Noise Level (PNL) or A-weighted
soundl pr.s.u.•ure Ic.vel uBAI for rating the efft-cts of helicopter noise on listeners.
Surnm:arv
Tlhi.s Aurk dlemonstrates that thu existe.'nce of blad., slap or tall rotor whine In ah,.livC,,jter noise :,p'(trum mnake:s I he rating nicl.ures fair from accurate. The paper
rekujnnimnds that a nv% :tpprav'h to thte rating (f heli.opter noise be developed.
C'omp:irlson With Similnr lPaprs
It is possible that a biad.i slap noise rating factor could be called for in this paper.
Evaluation of Paper
This palpcr makes a g(xod cast- for the Inaccuracy of conventional noise rating.Schtem4s in dvaling with spectra containing impulsive noise.
130
Munch, C. L. " "Prediction of V/STOL Noise for Application to Community Noisef•)sure", kDtpartmunt of Transportation Report No. DOT-TSC-OST'-73-19, May
The objective of this program was to develop a computer program for the predic-tion of Effective Perceived Noise Level (EPNL), tone corrected Perceived NoiseLevel (PNLT), and the A-weighted sound pressure level (dBA) of a V/STOL vehicleas it flies along a prescribed takeoff, cruise, and landing flight path.
Summary
The objectives described above are achieved. Procedures used to predict noiseradiation by helicopter rotors, propellers, turboshaft engines, lift and cruise fans,and jets are described in detail. A program and users' guide are furnished. Impul-sive type rotor noise from helicopters is not treated, nor is noise from deflected jets,augmentor wings, blown flaps, and other high-lift devices for which definitive predic-tion methods were not yet available.
Compariaon With Similar Papers
This is a good program to evaluate operational and design change impact on noiselevels of a variety of aircraft.
Evaluation of Paper
This report shows excellent correlation for turboshaft powered helicopter andturboprop STOL cases which were the only ones checked. it is considered a veryuseful program for providing aircraft noise input to V/STOL port planning studies.
h~t
.,Iu:;,'h, C. L.. and Kilg, .. un.mn ity Acccptafle of helicopter Noise: Criteria
.an,! \[,pl ca'io". NASA (CR-132430, lT7.1.
I, od'liic criteria for n init of , ivil ht-lic upt rsi to make tIheir iperations accept-
d W. to tO cm,1 mu L1itity- ignbo r•rg t'r'i ninals :an flight paths an:d to evaluate a current'
.i-mTrAtio!l Vivil transport h.licopt,.r against this crittrion to dutermine the operating
u.nitlitions, teriminal arva rtcquirntments, and a:'oustical modifications necessary forco n iIl rimcu .
Su n__I 1:k ry
" h• .ritj.rion found to lic uiiiipatjihl - ith '-intimuiuties was the Day-Night NoiseI.Lvel ILDtN at a constant hv'. i 11 6;0 dBA for ,nmbients up to :-, dBA and an "impactto ambient" ,f 2 dBA for ambients above this level. This criterion was found to be i•naccordance %%ith multinational aircraft noise regulated levels, with state regulations,and %ith 'onmioanity noise ordintances In existence at the time. It was determined thatthe unmodiurlhd helicopter met the ( riterion in cruise flight at typical alttudes, butmodifications to the main ant tail rotors and the engines were necessary f3r terminalarea operations to attain reali!-tic land area requirements.
Comparison With Similar Papers
This is the best case made' for use of d1lA and LDN in evaluating aircraft noiseand community impact. The study is p)arailhl to that of Reference 10.
Evaluation of Paper
*rhis was a comprehenlsve study which considered most current systems of rating
aircraft and community no)ise annoyance. It coecludes-ttiat the A-weightm. soundpressure level provides the best comi.,riation of accurary and practicality for use In
rating community reaction to helicopter noise. It uses this number as the basis for a
comnprehin.9ivv rating zicht-mt ',mji-h cortibnes the ,,ffecta of sound level, soun,- dura-
tion, ambicrt rxnlse I.evel, time of day, numix.r of flights, and the human hearing
response. A unique criterion is also developed to identify the presence of rotor bladeslap in a helicopter noise signature and to quantify the effect.
132
,.I!,rhead, J. B., "Acoustic Considerati'ns in the Dc.sign of a Quiet Helicopter",\k - L; Lalxoratories Technical Report MR70-3.
The purpo.e of this study was tu relate certain helicopter design and operationparameters to the production of noise and its resultant aural detection.
Sumniary
This paper reviews acoustic factors to be considered in the design of quiet heli-copters and the basics of aural detection, discusses Lowson type methodology forrotor noise prediction, and presents some trends for design and operation parametersto yield up to 20 to 1 reductions in aural detection distance relative to conventionalhelicopters designed with no regard to the aural detection problem.
Comparison With Similar Papers
Although quantitative comparisons of annoyance versus aural detectability aredifficult to make, this'paper could supplement References 9, 10, and 13 in outliningdesign practice for low noise generation in helicopters.
Evluation of Paper
No unique Information Is presented, but a good review of noise prediction andaural detection prediction techniques is provided In this report.
121'
oliorItY.Lt. J. B., "Scaling Aircraft Noise Perceptfon", Journal of Sound and Vibra-
ti.n, \',u:'.•c 26;, No. 3, 19(J7J.
'u rpo se
T. p'rformn extensive e'xpvrimentation to deter.nine the practical differences be-t-.%k.,,n .•;t,'rous alternativte methods for calculating the perceived levels of individual
Jai rcralt ;l)ov(Jr sounds.
Sunm .mar
Or•w- hundrtv.l and twenty recorded sounds, including jets, turboprops, piston air-(ralt, and hvlicopters &ere rate-d by a pantl of subjects In a p-ired comparison test.The rtsults wer,: analyi.cd to evaluate a number of noise rating procedures in termsof thcir ability to accurately e(stimate both relative and absolute perceived noisinessover a ,id.r dynamic range (84-115 dB SPL) than had generally been used in previousexperiments. The performances of the different scales were examined in detail fordifferent aircraft categories, and the merits of different band level summation proce-dures, frequency weighting (unction, and duration corrections were investigated.
•__)mparison With Similar Papers
This is a short form of the author's report. Reference 4. This is an extensivestudy using lA.-tter noise reproduction than most others.
Evaluation of Paper
Several conclusions from this study are: perception of low frequency harmonicsound (from helicopters particularly) needs further study as poor correlation was
attained; the influence of doppler shift on perceived noisiness Is not conclusivelyknow, as it seems important in laboratory simulations-but not In auctual-aircraft fly-
overs; tone corrections are not particularly beneficial below 500 Hz and ahould beignored it. this range, three dLB per doubling of the number o,1 exposures Is accurate.The data :shnws slight superiority of PNL and EPNL over dBA and EdBA (effectiveA-we-ighted sound pressure level). Standard deviations.between subjective andohJecti%,v data were 4.6 and 3. 5 for PNL and EPNL, respectively, and 4.9 and 4.2for dBA and EdIIA, respectively for helicopter noise.
lv'
.. . . . . . .. .. . . ..... . .. -
O',Li-rhead, J. B. and Lowson, M. V., "Problems of Helicopter Noise Estimation andHeduction"i ALUA P:ipcr No. 69-195, February 1969.
To present a solution for the prediction of helicopter rotor rotational noise andcicisgn charts ior reiuction of this type of noise.
Summaray
This paper presents a closed form solution for the prediction of helicopter rotorrotatiokal noise and design charts identifying parametric changes for its reduction.
)oise reduction requirements are derived on the basis of aural detection of the heli-copter.
Comparison With Similar Papers
This paper discusses noise reduction as keyed to aural detection, as was done byOllerhead t 2 . Aural detect!on is generally controlled by rotor rotational noise in heli-copters. This type of noise is also significant in annoyance in some cases.
Evaluation of Paper
This paper does not deal with the subjective evaluation of hellcopcar noise as awhole. However, it is useful In defining criteria for and the means to reduce rota-tional noise at extremely large distances, where it Is first detected aurally.
P,"".oas, K., ".ouiirt'.s Judgiv:';,t.s of iulhcuprA.-r Flyovers", FAA DS- 6 7 -1,"
"Nu dtiturmint th.e :q)Jlicability of ' several objective rating measures In predictingt.c .h;bj#,ti%(v' respistse to helicopter flyover noise.
Su'wmnarv
Tests %ere conducted in which 21 college students Judged the noisiness of eightrecorderd hcelt.,pt,.r flyover noises versus a jet transport flyover noise and a shaped
oIa.:,l of n.k~*. T'%sts were c'i)Tf'i cted Ini an ani'cholc chamber using primar'iy themethotd ,f pa:ired comparisons. I hft- rx.sults in licat, that the calculated PerceivedNoise Level (P.NL) is the be-st predictor oi noisiness, followed closely by the N-wlght-ed sound pressure level jdi.N) anfl the A-weighted sound pressure level (dBA). Dura-tion anti purj.-tonc corrections applied to the ca:culated PhL did not Improve the pre-diction accuracy of this measure.
Compari.son With Similar Papers
"Tfhus wi•rk was aime.d solely at helicopter noise. The conclusions are similar toth :-' (if kfr.rei-ces 2, 5, -;, 7 awl i 1.
Evaluatlon of Paper
Tlu.- report indicates that dBA is approximately the same accuracy as PNL injudging the subjective annoyance of helicopter noise.
'.I %
pears ins, K. S. and Bennett, R. L., "Htandbook of Noise Ratings", NASA CR-2376,
A 1974.
Purposc
To provide compilation, in a concise form, of information describing the multi-
tude of noise rating schemes which are in use today.
Summary
This book contains descriptions, title, unit, definition, applicable standards, pur-
pose, background, calculation method, and example of usage for rearly all current
noise rating schemes. Categories of rating schemes covered are: direct ratings of
sound level (Sound Level Meter type weighting functions which are not amplitude vary-
ing), computed loudness and annoyance ratings (including those variants dealing with
tone, duration, and number of repetition corrections), commurication interferenceratings, and community response ratings.
Comparison With Similar Darers
This report provides a su imary of all of the noise rating schemes discussed and
evaluated in the papers su:n'•ai~zed in this section.
Evaluation of Paper
This is an excellent "single source" of material on all of the significant methods
of rating noise effects on mau.
137
Stepnit wski, W. Z. and Schmitz, F. Ii., "Possibilities and Problems of AchievingCommunity Noise Acceptance of VTOL,, International Council of the AeronauticalS,'ienccs, ICAS Paper 72-34, September 1972.
Purpose
The purpose of this study was to investigate the reduction of the acoustical annoy-ance of VTOL aircraft by reduction at the source through aircraft design and by flightpath management.
Summary
This paper presents first a review of noise standards. Typical transport aviationnoise standards are shown which project 85 EP"dB by 1985. As current state-of-the-art rotary wing VTOL transports indicate an annoyance level of approximately 95EPNEdB, this goal requires a 10 dB reduction in noise level. However, recent studieshave shown that a relative elevation of the noise level above that of the backgroundrepresents a very important criterion of the acoustic tolerance. The results of thestudy indicate that up to 10 EPNdB above daytime background noise level will resultin essentially no reaction from the community, whereas a 20 EPNdB increase willcause widespread complaints. It is also pointed out that PNL or EPNL may not besuitable for true indications of subjective reaction to the noise from different types ofaircraft.
In the second part of the paper, the reduction of noise at the source is discussed.Although an attractive overall criterion for assessing the penalties of noise reductionis the direct operating cost, it is difficult to calculate and does not permit a directstep-by-step evaluation. Thus, the authors present their results as weight and/orperformance penalty vs. noise reductibn attainable. They present the major noisesources, which are in order of decreasing importance: blade slap, tail rotor rota-tional noise, main rotor noise, turbine engine noise, and transmission noise. Thephenomenon and alleviation of each-source are discussed in turn, including a discus-sion of the associated weight and performance penalties for noise reduction, Rotarywing, tilt rotor, and lift fan concepts are discussed.
It is concluded that for two typical suburban communities, a reduction in noiselevel at the source of about 10 PNdB is required for current state-of-the-art rotarywing aircraft, and more than 20 PNdB for lift fan concepts. However, reducing therotor tip speed (the most powerful noise reduction effect) for a 10 PNdB noise reduc-tion will result in large weight and performance penalties. Flight trajectory manage-ment has potential for reducing "footprint" area, but there are too many variables(specified level of annoyance, whether buffer strips are used, ambient noise level,etc.) for general assessment of the benefits of this approach.
,139
('otnt;:rison With Sin'ilar ,I•aprs
This paper presents a general overview of the major noise sources in Hellcoptersand other VTOL aircraft and their alleviation. Other general noise source mechanismsareC discusst)d by )llv1rhead1 2 , Cux1 3 , and others, and this paper presents no new in-
formation in this area. TLiC data from the Model 347 has been discussed elsewhere by
Hinterkeuser and Sturnfeldl 0 as has the use of trajectory changes by the same
authors 1 4 .
Evaluation of P.apeUr
This paper presents a good comprehensive review of the major noise sources in
VTOL aircraft and means for -alleviating the noise at the source and through take-off
and landing flight path olptirization. Although essentially no new Information Is pre-
sented, it does give the reader a good overview of the VTOL aircraft noise picture.
The major elements in assessing the community acceptance of VTOL aircraft
operation are well presented. However, this paper would be strengthened if it ad-
d(resaed the basic problem of assessing subjective reaction to very different noise
signatures (i.e., from. rotary wings to tilt rotors to lift fans) using PNdB units,
which have been shown to be inadequate for helicopters in general, particularly
in the case where blade slap occurs 1 ' 2,8,11
140
Stlvrafeld, H., .linterleuser, E. G., Hlackman, R. B. and Davis, J., "Acceptabilityaf VTOL Aircraft Noise Determined by Absolute Subjective Testing", NASA CR-2043,June 1972.
Purp~ose
To d(etermine the relative subjective acceptability of two VTOL aircraft soundsusing absolute subjective testing methodology and to investigate the effects of theapplication of noise criteria to VTOL aircraft.
Summary
A program was conducted in which test subjects evaluated the simulated sounds ofa helicopter, a tilt wlng and a turbojet aircraft (used as a reference). Over 20,000evaluations were made while the test subjects were engaged in work and leisure activ-ities. The effects of level, exposure time, distance and ndrcraft design on subjectiveacceptability were evaluated. It was found that the helicopter and tilt wing sounds hadto be 4 to 5 PNdB lower than the reference sound to be judged equal In annoyance forsounds 15 seconds in duration. It. was also found that the effects of noise durationdecrease when durations exceeded 120 seconds and that good correlation was obtainedbetween subjective ratings and acoustical measurements of helicopter and tilt wingVTOL sounds. Peak PN L, dBA, and dBC produced similar correlation.
Comparison With Similar Papers
The results presented in this paper correlate with those of References 1, 2, 6,7 and 11.
Evaluation of Paper
This report* indicates that PNL, dBA, and dBC produce similar results in pre-dicting annoyance of VTOL noise and that they all underpredict the annoyance relativeto subjective evaluation.
141
L. I'S, 1t. J. , "Jury' W..tings of ('umpk'x Aircraft Noise Spectra Vers.us Ca.lculatedRatings", ACOUSUtica Society of America, Soth Meeting, Novenmer 1970.
Purpost*
This paper present&,d the r..suit. of a study which had the objective of determining
the accuracy of several noise rating systems in prý,.lictlng the annoyance of severalfixed wing aircraft noie spectra.
Sunimarv
Engine noise spectra (15 in all, vere relcruduced inside at, anechoic listeningfacility and judged by a sound jui'.ý ,: :mn-yac. The method of adjustment proce-dure was used by the subjects tj st.( lidt tvst sonild iulaiivc to a :onstant jet noise type
reference sounld. The objective noise rating .aeasureb tested 'Mere: PNLT, ANL(Annoyance level), PNI,, dBA, dBB, dBC, and dBI). It is concluded that the ANLseems to rate actual engine noise spectra better than any of the other measures con-sidered in the study. ft is als,; concluded that the close agreement between resultsobtained with the two parallel methods of analysis (i.e., electrical signal analysisversus analysis of the acoustic signal in the test chamber) indicates that, with suffi-cient care, precise electrical atalysis can be made and may actually be better wherequestions of tUnc correction "t:. involved,
Comparison With Similar Papers
The ANL parameter has not attained general usage as have the PNL and spectrumweighting functions evaluated in References 1, 2, 5, 6, 7, 10, 11, 16 and 17.
Evaluation of Paper
Duration was not one ol "he factt a considered in this studý. Orly the spectrum
weighting functions and pure 'ones were used af: variables. Only .o of the. sevefirating scales yielded standard deviations :ut of llr.e with the rest. these were dBC
and 41BB. Of the remainder, ANL produced the lowest standard deviation (1.17). Itappears that the addd complexity of computing the values of P1LT, ANL, and PHLare not worth the extra trouble considering the similar correlation aqtained with the
simple weighted functions dBA and dBD. It also appears that dBA would be preferablefrom the point of view of availability on sound level meters and analysis equipmer.t.
142
RE FE RENCES
Rotor Noise
1. Gutin, I.., On the Sound Field of a lIotatmng Propeller. TM 1195, National dvisaoryCommittee for Aeronautics, Washington D.C., 1948.
2. Hubbard, H. H. and Regier, A.A., Free-Space Oscillating Pressures Near theTips of Rotating Propellers, Report 996, National Advisory Committer 'or
Aeronautics, Washington D.C., 1950.
3. Garrick, I. E. and Watkins, C. E., A Theoretical Study of the Effect of ForwardSpeed on the Free-Space Sound Pressure Field Arouad Propeller, Report 1198,National Advisory Committee for Aeronautics, Washington D.C., 1954.
4. Watkins, C. E. and Durling, B.J., A Method for Calculation of Free-Space SoundPressures M-tar a Propeller in Flight Including Consideration of a ChordwkseBlade Loading TM 3809, National Advisory Committee for Aeronautics,Washington D.C., 1956.
5. Lowson, M. V., "The Sound Fleid for Singularities in Motion," Proceedingsof the Royal Society, A. Vol. 2h;, 1965, pp. 559-572.
6. Schlegel, R., King, R., and Mull, H., Helicopter Noise Generation and Pro-pagation, USAAVLABS Technical Report 66-4, October 1966.
7. Lowson, M. V., and Ollerhead, J. B., Studies of Helicopter Rotor Noise,USAAVLABS Technical Report 68-60, January 1969.
8. Schlegel, R. G. . and Bausch, W. E., Helicopter Rotor Rotational Noise Pre-diction and Correlation USAAVLABS Technical Report 70-1, November 1970.
9. Wright, S. E., "Sound Radiation From a Lifting Rotor Generated by AsymmetricDisk Loading," Journal of Sound and Vibration, Volume 9, Number 2, 1969,pp. 223-240.
10. Loewy, R. G., and Sutton, L. R., "A Theory for Predicting the Rotational Noiseof Lifting Rotors In Forward Flight, Including a Comparison With Experiment,"Journal of Sound and Vibration, Volume 4, Number 3, 1966, pp. 305-344.
11. Sternfeld, H., Bobo, C., Carnklch.ei, D., Fukushima, T., and Spencei, R.,An Investigation of Noise Generation on a Hyovering Rotor, Part 11, U.S. ArmyResear'ch Office - Durham, !Ieport D210-10550-1, November 1972.
143
i.. iHosier, 0. N. .and Ramakrishnan, It., and Pek'g, R.J., "The Prediction of RotorRotational Noise Using Measured Fluctuating Blade Loads," Presented at the 30thAnnual National Forum, American Helicopter Society, Preprint No. 80L, May1974..
13. Leverton, .1.W., "The Noise Characteristics of a Large 'Clean' Rotor,"Journal of Sound and Vibration, Volume 27, Number 3, April 1973, pp. 357-376.
14. Lowson, M. V., Whatmore, A. It., and Whitfield, C. E., Source Mechanlama forRotor Noise Radiation NASA Contractor Report 2077, August 1973.
15. Bausch, W. E., Sikorsky Methodology Review and Recommendation RagardingPrediction of Helicooter Rotor Noise, Report prepared under NASA PurchaseOrder No. L-5723A, 1974.
16. Leverton, J., and Pollard, J., "A Comparison of the Overall and BroadlbadNoise Characteristics of Full-Scale and Model Helicopter Rotors," Journal ofSound and Vibration Volume 30, Number 2, 1973, pp. 135-152.
17. Ffowcs-Williams, J. E., and Hawkings, D.L., "Theory Melatng to Noise aiRotating Machinery," Journal of Sound and Vibration, Volume 10, Number 1,July 1969, pp. 10-21.
18. WlClnalk, S. E., "A Correlation of Vortex Noise Data From Helicopter MainRotors," Journal of Aircraft, Volume 6, Number 3, May-June 1969, pp. 279-281.
19. Munch, C. L., Prediction of V/STOL Noise for Application to CommunityNoise Exposure, Department of Transportation Report DOT-TSC-OST-73-19,May 1973.
20. Leverton, J.W., Helicopter Noise - Blade Slapi-Part 1: Review and TheoreticalSuyNASA CR-1221, October 1968.
21. LUvertonr, J.W., Hlelicopttcr Noise - Blade sla.1 Part 2: Experimental Results,NASA CR-1983, March 1972.
22. Widnall, S. , "Hlelicopter Noise Due to Blade-Vortex Interaction," Journal ofthe Acoustical Society of America, Vc ume 50, Number 1, 1971, pp. 354-365.
23. Bausch, W. I-., Munch, C. L., and Schlegel, R. G., An Experimental Stiday ofiic0copter Rotor Impulsive Noise, USAAVLABS Technical Report 70-72, 1971.
24. Fliotas, L.T. , 'Vortex Induced Helicopter Blade Loads and Noise," Journalof Sounj.,and Vibration, Volume 27, Number 3, 1973, pp. 387-398.
144
25. ilinterkeuser, G., and Sternfeld, Ii., Jr., Civil Helicopter Noise Assessment
Studs, Boeing Vertol Model 347, CR-132420, NASA, Washington D.C., 1974.
26. Arndt, R.E.A., and Borgman, D.C., "Noise Radiation From Helicopter Rotors
Operating at High Tip Mach Number," Presented at the 28th Annual Forum,
American Helicopter Society, June 1970, Preprint 403.
27. Lyon, R. H., Mark, W. D., and Pyle, R.W., Jr. , "Synthesis of Helicopter
Rotor Tips for Less Noise," Journal of the Acoustical Society of America,
Volume 53, Number 2, 1973, pp. 607-618.
28. Hubbard, H. H., Lansing, D. L., and Runyan, H. R. , "A Review of Rotating
Blade Noise Technology", Journal of Sound and Vibration Volume 19, Number
3, 1971, pp 227-249.
29. Morfey, C.L., "Rotating Blades and Aerodynamic Sound". Journal of Sound
and Vibration, Volume 28, Number 3, 1973, pp 587-617.
Englne Noise
1. Lighthill, M.J., "On Sound Generated Aerodynamically: I, General Thecry,"'Proceedings of the Royal Society, A, Vol. 211, 1952, pp. 564-587.
2. Lighthlll. M.J., "On Sound Generated Aerodynamically: 11, Turbulence as aSource of Sound," Proceedings of the Royal Society, A., Vol. 222, 1954, p. 1.
3. Bushell, K.W., "A Survey of Low Velocity and Coaxial Jet Noise with Applicatloain Prediction," Journal of Sound and Vibration. Vol. 17, No. 2, 1971, pp. 271-282.
4. Ho, P. T. and Tedrick, R. N., "Combastion Noise Prediction Techniques forSmall Gas Turbiae Engines," Inter-Noise 72 Proceedins, 1972, pp. 507-512.
5. Grande, E., Brown, D., Sutherland, L., Tedrick, R.. Small Turbine EngineNoise Reduction, Vol. U1, AFAPL-TlR-73-79, Air Force Aero PropulsionLaboratory, Wright-Patterson Air Force Base, Ohio, 1073.
6. Motainger, R., Prediction of Engine Combustor Noise &ad Correlation WithT64 Engine Low Frequency Noise. Report No. R72AEG313, 'eneral ElectricCompany, 1972.
7. Nietzel, R. L., Lee, R. and Charay, A.J.. 9SY,'1. Trak n1 Firal Report.Engine and Installation Preliminary Design CR-134738, NASA, WashingtonD.C., 1973.
8. Gerend, R. P., Jumasaka, H. P., and Roumdhill, J. P.. "Core Engine Noise,"Paper No. 73-1027, American Institute of Aeronautics asd Astronautics,October 1973.
9. Grande, E., "Core Engine Noise," Paper No, 73-1026, American Institute ofAeronautics and Astronautics, October 1973.
10. Dunn, D.G. and Peart. N.A., Aircraft Noise Source end Contour Estimation,CR-114649, NASA, Was~hington D.C., L973.
11. Huff, R.G., Clark, B.J. and Dorsch, R.G., Interim Prediction Method for LowFrequency Core Engine Noise TMX-71627, NASA, Washington D.C., 1974.
:2. Anon, Jet Noise Prcdiction, Aerospace Information Report 876, Society clAutornotive Engineers, 1965.
13. Kazin, &. B., 0't. a!., Core I.ridrz Noise Ccontrol PrcgrKm. (3 Volumes),DOT-FA72W-3023, Federal Aviation Administration, Washington D.C., 1975.
146
14. Strahle, W.C. 0 "A Review of Combustion Generated Noise," Paper 73-1023,American Institute of Aeronautics and Astronauti:s, October 1973.
15. Pickett, G.F., "Turbine Noise Due to Turbulence and Temperature Fluctuations,"Paper presented at the 8th International Congress on Acoustics, London, July 1974.
16. Mathews, D.C. and Peracchio, A.A., "Progress in Core Engine and TurbineNoise Technology," Paper No. 74-948, American Institute of Aeror.autics andAstronautics, August 1974.
17. Smith, M. J.T. and Bushell, K.W., "Turbine Noise - Its Si inificance in the CivilAircraft Noise Problem," Paper No. 69-WA/GT-12, Amer.can Society ofMechanical Engineers, 1969.
18. Smith, M.J. T. and House, M. E., "Internally Generated Noise from Gas TurbineEngines: Measurement and Prediction," Transactions of the American Societyof M•echanical Engineers: J. of Engineering for Power, April 1967, pp. 177-190.
19. Burdsall, E. A. and Urban, R. K., Fan-Compressor Noise: Prediction, Researchand Reduction, FAA -RD-71-73, Federal Aviation Administration, WashingtonD.C., 1971.
20. Benzakian, M.J. et. al., Fan/Compressor Noise Research. (Four Volumes),FAA-RD-71-85, Federal Aviation Administration, Washington D.C., 1972.
21. Gutin, L., On the Sound Field of a Rotating Propeller, TM-1195, NationalAdvisory Committee for Aeronautics, Washington D. C., 1948.
22. Lowson, M. V., "The Sound Field for Singularities in Motion," Proceeding ofthe. Royal Society, Vol. 286, 1965, pp. 559-572.
23. Lowson, M. V., Theoretical Analyses of Compressor Noise CR 1287, NASA,Washington D.C., 1969.
24. Allen, C. Ii., Noise Reduction, (L. L. Beranek, Ed.) McGraw I1ill Book Company,New York, 1960.
25. Bowes, M.A., Te'st axd Evaluation oi a Qcuiet fellcopter Configurat.on HTII.42fl,Technical Report 71-31, U.S. Air Mobility Research and Development i.ar4oratory,Fort Eustis, Va., 1972.
26. Tyler, J. M. and Sofrin, T. B., "Axial Flow Compressor Noise Studies," Pbper345D, 1961 SAE Aeronautical Meeting.
- -•'g. --- • '.- .""-.. . --- ' • •-- .. . ... .•- -•... . .. m ,,. • ,..-,
_7. Shahady, P.A., Lyon, C.A., Tedrick, R.M., and H!idenbrand, R.W., "Reductioaof Noise from Small Turbopropulsion Engines", AIAA Paper No. 74-.9, Preaetedat the AIAA 12th Aerospace Sciences Meeting, January 1974.
2?. Kazin, S. B., and Emmorling, J.J., "Low Frequency Core Engine Noise", ASMEPaper No. 74-WA/AERO-2, November, 1974.
.v. Haydden, R. E., Nolae from Interaction of Flow With Rilgd Surfaces: A Reviewof Current Status of Pred.tlon Techniques, NASA CR2126, October, 1972.
30. Caadel, S. M., Analytical Studies of Same Acoustic Poblemas of Jet EzignssPhd Thesis, Califorana institute of Tochnology, 1972.
31. Cumpsty, N. A. and Marble, F. E., The Generation ot Noise by the Fluctuations
in Gaa Tenperature in a Turbine, Cambridge University Department a Engimer-ing Report CUED/A TURBO/TR57, 1974.
32. Priede, T., "Noise of Diesel EnWAg Injection Equipment", Journal of Bound adVibration, Volume 6, Number 3. 1967, pp 443-459.
148
Gearbox Noise
1. Laskin, I., Orcutt, F. K., Shipley, E.E., Analysis of Noise Generated by UH-1Helicopter Transmission, USAAVLABS Technical Report 68-41, June 1968.
2. Badgley, R. H., Hartman, R. M., "Gearbox Noise Reduction: Prediction andMeasurement or Mesh-Frequency Vibrations Within an3 Operating HelicopterRotor Drive Gearbox", ASME Paper No. 73-DET-31, September 1973.
3. Badgley, R. H., Laskin, I., Pr& a for Pelicopter Gearbox Noi3e Predictionand Reduction, USAAVLABS Technical Report 7t#-12, March 1970.
4. Hartman, R., Badgley, R., Model 301 HLH/ATC Transmission Nuise ReductionProgram, USAAVLABS Technical Report (Cuntract DAAJO1-71..C-0840 (P40)),January 1973.
5. Sternfeld, H., Schairer, J., and Spencer, R., An Investigation of HelicopterTransmission Noise Reduction by Vibration Absorbers and Dsmping, USAAMRDLTechnical Report 72-34, August 1972.
6. Grande, E., Brown, D., Sutherland, L., Tedrick, R., Small Turbine EngineNoise Reduction, Volume II. Noise Prediction Methods. Air Force Aero Pro-pulsion Laboratory Tech. Report AFAPL-TR-73-79, Volume II, December1973.
7. Bowes, M.A., Test and Evaluation of a Quiet Helicopter Configuration HH-43B,U. S. AAMRDL Technical Report 71-31, January 1972.
8. Barlow, W.H., McClusky, W. C. , and Ferria, H.W.-, OH-6A Phase II Quiet.Helicopter Program, USAAMRDL Technical Report 72-29, 1 ptember 1972.
9. Pegg, R.J., Henderson, H. R., and lilton, D.A. , Results of the Flight NoiseMeasurement Program Using a Standard and Modified SH-3A HIelicopter NASATechnical Note D-7330, December 1973.
ilelic'-pter N Pjciredic~or
1. D)unn, D. G. and Peart, IN.A. , Aircraft Noise Source and Contour Ectimation.CH-1146349, NASA, JulY 19713.
2. Munch, C. 1.. Prediction of v Is-roi.- Nt'iise for Applcation to Commatynt NoiseEýLoaure, 1X-pt. of Transportat~on freport No. D)OT-TSC-OST-73-19, May 1973.
3. Lowson, M!. V. and Ollerhead, J. B. , Studies of IHelleopter Rotor Noise,LSAAVLABsS Trectmic:.i HReport 6;5-60, January 1969.
4. Sc-hlvgel, R. , King, R. and Mull, H. , Helicopter Noise Generation and Propa-giUn SAAVLAIJS Technical Report 66-4, October 1966.
1.50
F
Helicopter Noise Reduction Techniques
1. Hirsh, N. B. and Ferris, H.W., "Design Requirements for a Quiet Helicoptcr",American Helicopter Society Preprint 604, May 1972.
2. Barlow, W. H., McCluskey, W.C. and Ferris, H.W., OH-6A Phase II QuietHelicopter Program, USAAMRDL Technical Report 72-29, September 1972.
3. Bowes, M.A., Test and Evaluation of a Quiet Helicopter Configuration HH-43B,USAAMRDL Technical Report 71-31, January 1972.
4. Schlegel, R. G. , Hush Final Report - Quiet Helicopter Program, Sikorsky Air-craft Report No. SER-611478 (Contract DDA J02-69-%.-0020), January, 1970.
•..o
151
.......-t-.- ~- a-.---
Subjective lesponse to Helicopter Noise
I. Pearsons, k.S., Noisiness Judgements of Helicopter Flyovers, FAA DS-67-1,5 January 1967.
"2. Hfecker, M. H. L., Kryter, K. D., Comparisons Between Subjective Ratings ofAircraft Noise and Various Objective Measures, FAA No-68-33, April 1968.
3. ollerhead, J. B., The Noisiness of Diffuse Sound Fields at High Intensities,FAA-NO-70-3, August 1969.
4. Ollerhead, J. B., An Evaluation of Methods for Sealing Aircraft Noise Perception,NASA CR-1883, October 1971.
5. Stv'rneld, H., Hinterkeuser, E.G., Hackman, R. B., Davis, J., Acceptabilityof VTOL Noise Determined by Absolute Subjective Testing, NASA CR-2043,June 1972.
6. Ollerhead, J. B., "Scaling Aircraft Noise Perception," Journal of Sound andVibration, Vol. 26, No. 3, 1973.
7. Adcock, B. D., Ollerhead, J. B., Effective Perceived Noise Level Evaluated forSTOL and Other Aircraft Sounds, FAA-NO-70-5, May 1970.
8. Leverton, J. W., "Helicopter Noise-Are Existing Methods Adequate For RatingAnnoyance or Loudness," Journal of the American Helicopter Society, April 1974.
9. Munch, C. L., Prediction of V/STOL Noise For Application to Community NoiseExposure, Dept. of Transportation Report No. DOT-TSC -OST-73-19, May 1973.
10. Hinterkeuser, E.G., Sternfeld, H., Civil Helicopter Noise Assessment Study-Boeing Vertol Model 347, NASA CR-132420, May -1974.
11. Munch, C. L., King, R.J., Community Acceptance of Helicopter Noise: CriteriaAnd Application, NASA CR-132430, 1974.
12. Ollerhead, J. B., Acoustic Considerations in the Design of a Quiet Helicopter,Wyle Laboratories Technical Report WR70-3.
13. Cox, C. R., "Helicopter Noise Reduction and its Effects on Operations", PaperNo. 352 in the Proceedings of the 25th American Helicopter Society Forum, May1969.
152
i.
14. Schmitz, F. H. and Stepniewski, W. Z., "Reduction of VTOI: Operational NoiseThrough Flight Trajectory Management," AIAA Journal of Aircraft, Volume 10,Number 7, July 1963.
15. Halwes, D. R., "Flight Operations to Minimize Noise", Vertiflite (AmericanHelicopter Society), February 1971.
16. Hinterheuser, E.G., Sternfeld, H., Subjective Response to Synthesized FlightNoise of Several Types of V/STOL Aircraft, NASA CR 1118, August 1968.
17. Fidell, S.', and Peasons, K.S., Study of the Audibility of Impulsive Sounds,NASA CR 1598, May 1970.
153/154
HELICOPTER NOISE BIBLIOGRAPHY
Adcock, B.D. and Olierhead, J. B., Effective Perceived Noise'Level Evaluated for STOL
and Other Aircraft. FAA-NO-70-5, Federal Aviation Administration, Washington,
D.C., 1970.
AGARD, Fluid Dynamics of Rotor and Fan Supported Aircraft of Subsonic Speeds.,AGARD Conference Proceedings No. 22, September 1967.
d'Ambra, F., Dedleu, J. P. and Julienne, A., "Measurements of Helicopter Noise inFlight (Measure de Briet d'Hclicopters en Vol)" TP No. 1136, Office Nationale D'Etudesel de Researchers Aerospatiales, France, 1972.
Amiet, R. K., Acoustic Radiation from an Airfoil in a Turbulent Stream, Report
N111208-2, United Aircraft Research Laboratories, East Hartford, Conn., 1974
Amor, C.B., and Leverton, J.W., "An Investigation of Impulsive Rotor Noise Usinga Model Rotor", J. of Sound and Vibration Vol. 28, pp. 55-71, 1973.
Anon. " Effects of Noise on Commercial V/STOL Aircraft Design and Operation",A68-44938, Boeing Co., Seattle, Washington, 1968.
Anon. "Frequency Weighting Network for Approximation of Perceived Noise Level forAircraft Noise", SAE ARP 1080.
Anon., "Helicopter and V/STOL Noise Generation and Suppression," Report of theResults of a Joint U.S. Army, National Academy of Sciences, National Academy ofEngineering Conference, Washiagton, D.C., July 30-31, 1968.
Anon., Impact Characterization of Noise Including Implications of Identifying andAchicving Levels of Cumulative Noise Exposure, Environmental Protection Agency Air-craft/Airport Noise Study Report NTID 73.4, 1973.
Anon., Jet Exhaust Noise Prediction, (Proposed revision of AIR 876), Rolls-RoyceLimited, England. Second Draft, October 1973.
Anon. , Standard Values of Atmospheric Absorption as a Function of Temperature andHumidit, for use in Evaluating Aircraft Flyover Noise, SAE-ARP-866, 1964.
Arndt, R, E.A., and Borgman, D.C., "Noise Radiation from Heliccpter Rotors Oper-ating at P igh rip Mach Numbers", Paper presented at the 16th Annual National Forumof the American Helicopter Society, Washington, D.C., June 1970.
Arnold, James S., "Generation of Cowbustloa Noise," J. of Acoustic Soc. of Amer.,Vol. 52, Number 1 (part 1), January 14, 1972.
155
Arnoldi, R.A., Near-Field Computations of Propeller Blade Thickness Noise. ReportR-096-1, United Aircraft Corporation Research Department, East Hartford, Conn.August 1956.
Arnoldi, R.A., Propeller Noise Caused by Blade Thickness. Report R-0896-1, UnitedAircraft Corporation Research Department, East Hartford, Connecticut. January 1956.
Baczek, L. "An Experimental Investigation Concerning Trailing Vortex and HelicopterRotor Blade Interaction", M.S. Thesis, MIT, Cambridge, Mass., 1970.
Badgley, R. H. and Hartman, R. M., "Gearbox Noise Reduction: Prediction and Mea-surement of Mesh-Frequency Vibrations Within an Operating Helicopter Rotor DriveGearbox", Paper No. 73-DET-31, American Society of Mechanical Engines, 1973.
Badgley, R.H. and Laskin, I., Program for Helicopter Gearbox Noise Prediction andReduction, TR 70-12, U. S. Army Aviation Material LaboratL, les, Fort Eustis, Va.,1970.
Banerian, G., "A Look at the Duration Correction for Computing EPNL", J. of Soundand Vibration, Vol. 23, No. 4, 1972.
Barlow, W. H., McCluskey, W. C., and Ferris, H.W., OH-6A Phase II Quiet Helicopter Program, TR-72-79, U. S. Army Air Mobility Research and Development Labor-atory, Fort Eustis, Va., 1972.
Barry, B., "Subsonic Fan Noise," J. of Sound and Vibration, Vol. 7. No. 2, pp. 207-220, 1971.
Barry, F. W. and B. Magliozzi, Noise Detectability Prediction Method for Low TipSpeed Propellers. Tech. Rept. AFAPL-TR-71-37, Wright-Patterson Air Force Base,Ohio. June 1971.
Bateman, D.A., et al; Compressor Noise Research, FAA-ADS-31, Federal AviationAdministration, Washington, D.C. 1965. 7 - _
Bauer, B. B., and Tcrick, E. L., "Researches In Loudness Measurement", I.E.E.E.Transaction on Audio and Electro-acousttcs, Vol. AU-14, No. 3., pp. 141-151, Sept.1966.
Bausch, W. E., Munch, C. L., and Schlegel, R. G., AN EXPERIMENTAL STUDY OFHELICOPTER ROTOR IMPULSIVE NOiSE, USAAVLABS TR-70-72, U.S. ArmyAviation Material Laboratories, Fort Eustis, Va., 1971.
Becker, R. A., "Noise Reduction Design in the Small Helicopter", Vertiflite, Vol. 16,No. 4, pp. 14-18, 1970.
156
B01 Helicopter Company, A Study of the Origin and Means of Redhicing Helicopter Noise,Unites States TCREC Tech Report No. 62-73, Nov. 1962.
Benzakein, M. J., et al; Fan/Compressor Noise Research, FAA-RD-71-85, Four Vol-umes. Federal Aviation Administration, Washington, D.C. 1972.
Beazakein, M.J. and Kazin, S. B., "A Theoretical Prediction of Aerodynamically Gen-erated Noise In Fans and Compressors," Paper presented at the Acoustical Society ofAmerica Conference in Cleveland, Ohio, November. 1968.
Benzakein, M. J., and Morgan, W. R., "Analytical Prediction of Fan/Compressor Noise,ASME Paper 69-WA1GT-10. 1969.
Bishop, D. E., Frequency Spectrum and Time Duration Descriptions of Aircraft Fly-Over Noise Signals, FAA-DS-67-6, Federal Aviation Agency, Washington, D. C.
Bishop, E. E., "Helicopter Noise Characteristics for Heliport Plarning," FAA-ADS-40,Federal Aviation Administration, Washington, D. C. 1965.
Bishop, D. E., "Judgement of the Relative and Absolute Acceptability of AircraftNoise", J. of the Acoustical Society of America, Vol. 40, No. 1, pp. 108-122, 1966.
Bishop, D. E., and Horonjeff, R. D., Noise Exposure Forecast Contour Interpretationsof Aircraft Noise Trade-Off Studies FAA NO-69-2, Federal Aviation Administration,Washington, D. C., 1969.
Bishop, D.E., and Horonjeffi R.D., Procedures for Developigt Noise Exposure Fore-cast Areas for Aircraft Flight Operations, FAA-DS-67-10, Federal Aviation Agency,Washington, D.C., 1967.
Blazier, W. E., "Criteria for Control of Community Noise", Paper presented at themeeting of the Acoustical Society of America, November 1967.
Blum'enthal, V. L., Streckenbach, J. M., Tate, R. B., "Aircraft Environmental Prob-lemt, " AIkA Paper 73-5, 1973.
Borsky, P. N., "Noiso as Perceived by the Coimmunity", Proceedings of the SAE/DOTConference on Aircraft and the Environment, Washington, D. C., 1971.
Borst, H. V., "Review of V/STOL Aircraft with Tilt-Propellers and Tilt Rotors,"of the Royal Aeronautical Society, Sept. 1968.
Bowes, M.A., "Test and Evaluation of a Quiet Helicopter Configuration HH-43B",J. of the Acoustical Seciety of America, Vol. 54, No. 5, pp. 1214-1218, 1973. Also, TTR 71-31, U.S. Army Air Mobility Research and Development Laboratory, Fort Eustis,Va., 1972.
157
lirt-gman, 11. L. and Pearson, R.R., Development of a Noise Annoyance SensitivityScale, CR-1957, NASA, Washington, D.C., 1972.
lirown, D., "Analyses of Propeller Vortex Noise", Paper presented at the Slat meet-i:•g of the Acoustical Society of America, April, 1971.
llrwk;n., 1). and (llerhead, J. B., Propeller Noise at Low Tip Speeds AFAPL-TR-71-55, Wr•.-ight Pattersen Air Force Base, Dayton, Ohio. 1971.
Burdsall, E.A. and Urban, R. 1l., F.an-Compressor Noise: Prediction, Research,and Reduction Studies, F"AA -Rl)-71-73, Federal Aviation Administration,Washington, D.C., Fcbrua'ry 1971.
Burpo, F. B. and Lynn, R. it., Measurement of Dynamic Airloads on a Full ScaleSemi-Rfigid Rotor Bell Helicopter Company, TCREC Technical Report 62-42, U.S.Army Transportation Research Command, Fort Eustis, Virginia, December 1962.
CAL/AVLABS, Proceedings of the Third CAL/AVLASS S3-m psium, Vol. I: Rotor/Propeller Aerodynamics - Rotor Noise, June 18-20, 1969.
Carpenter, P. J., Lift ano rofile Drag Characteristics of a NACA 00.12 AirfoilSection as Derived from Measured lielicopter Rotor Hovering Performance, NACATN 4357, Washington, D.C. 1958.
Carter, N. L., "Effects of Rise Time and Repetition Rate in the Loudness of AcousticTransients", J. of Sound and Vibration, Vc.l. 21, No. 2, pp. 227-239, 1972.
Chandrashekhara, N., "Some Studies of Tone Generation in and Radiation from Axial-Flow Fans," PhD Thesis, University of Southampton, 1970.
Chestnutt, D., Fetler, C. E. and Hubbard, H. H., "Trends in Noise Control for Air-craft Gas Turbine Power Plants," NASA, Washington, D.C.
Chichester, Miles, and Romer, D. R. M. "The Impact of VTOL Aircraft on AirpoitDesign and Development," J of the Royal Aeronautical Society, Vol. 75, August 1971.
Christensen, C. M., "The sound Field of a Compressor Rotor," Masters of ScienceThesis, M. I. T., June 1968.
Civil Aeronautics Board, "Direct Exhibits and Direct Testimony of Pioneer AirlinesInc. in the Reopened Waebingtor,-.Baltimore Helicopter Service Investigation", Docketr17665 et. al., Washington, D. C., July 19, 1971.
158
Clark, D. R., and Leiper, A C., "The Free Wake Analysis, Method for the Predictionof Helicopter Rotor Hovering Performance," J. of the American Helicopter SccletyVol. 25, No. 1, 1970.
Clark, L. T. ,"Noise Generation by Turbomachines," D6-20393, Boeing Co., Seattle,Wash., April 1965.
Clark, P.J. F. and Ribner, H.S., "Direct Correlation of Flactuating Lift With RadiatedSound for an Airfoil In Turbulent Flow," J. of the Acoustical Society of America.Vol. 46, No. 3, Fp. 802-805, 1969.
Clark, F.RI. and Kryter, K. D., Perceived Noisiness Under Anechoic, Semi-Reverh-erent, and Earphone Listening Conditions, CR-2108, NASA, Washington, D.C., 1972.
Cohen, A., "Airport Noise, Sonic Booms, and Public Health", Proceedings of theSAE/DOT Conference on Aircraft and the Environment, Washington, D.C.. 1971
Cohen, A., el. al., Correlation of Objection ability Ratings of Noise With ProposedNoise - Annoyance Measures, N 66 24828, U.S. Department of Health, Education andWelfare, 1964.
Cole, J. N. and Engi d, R. T., Evaluation of Noise Problems Anticipated with FutureVTOL AlrcraLft, Al. L-TR 66-245. Wright-Patterson Air Force Base, Dayton, Ohio,1967.
Conner, W. K. and Patterson, H. P., Community Reaction to Aircraft Noise AroundSmaller City Airports, CR-2104, NASA, Washington, D.C., 1972.
Cox, C. R., "Aerodynamic Sources of Rotor Noise," J. of the American HelicopterSociety, Vol 18, No. 1, pp. 3-9, January, 1973.
Cox, C.iR., "Full Scale He.icopter Rotor Noise Measurements in Ames 40 x 80 FootWing Tunnel ," Bell Helicopter Report No. 576-099-052, September 1967.
Cox, C. R., "Helicopter Noise and Passive Defense," American Helicopter Society,19th Annual National Forum, A63-18693, p. 156-163, 1963.
Cox, C. R., "Helicopter Noise Reduction and its Effect on Operations", Paper No. 352,Proceedings of the 25th Amnerican Hlihlcopter Socinty Forum, May 1969.
Cox, C.R., "Rotor Noise Measurements in Wind Tunnels." Proceedings of the ThiJCAL/AVLABS Sympostum, Volume 1, Aerodynamics of Rotary Wing and V/STOL Air-craft. June 190.9,
159
Cox, C. R., "Subcommittee Chairman's Report to Membership on Aerodynamic Sourcesof Rotor Noiso," Presented to the 28th Annual Forum of the American Helicopter Society,May 1972.
('ox, C. R., and Lynn, R. R., A Study of the Origin and Means of Reducing HelicopterNoise, TCREC-TR-62-73, November 1962.
Crirni, P., "Prediction of Rotor Wake Flows," Propeller and Rotor Aerodynamic. ,
Vol. of the CAL/USAAVLABS Symposium Proceedings, June 1966.
Crosse, G. W., et. al., "A Controll3d Experiment on the Perception of HelicopterRotor Noise," J. of the Royal Aeronautical Society, Vol. 64, pp. 629-632, 1960.
Curie, N., "The Generation of Sound by Aerodynamic Means," J. of the Royal Aero-nautical Society, Vol. 65, No. U11, pp. 724-728, 1961.
Curie, N., "The Influence of Solid Boundaries Upon Aerodynamic Sound," Proceduresof the Royal Society, 231A, pp. 505-514, 1955.
Davidson, 1. M., and Hargest, T. J. , "Helicopter Noise," J. Royal Aeronautical Society,Vol. 69, pp. 325-336, May 1965.
Davies, D. O., and Coplin, J. F., "Some VTOL Powerplant Design and DevelopmentExperience," J. of the Royal Aeronautical Society, Vol. 70, pp. 977-986, Nov. 1966.
Day, H. P., A Theory for Tip Stall Noise of Helicopter RotorsReport N412344-1,United Aircraft Research Laboratories, East Hartfort, Conn., 1974.
Dean, L.W., "Broadband Noise Generation by Airfoils in Turbulent Flow," AIAAPaper 71-587, Palo Alto, C2lif., June 1971.
De Belleval, J. et. al, Studies of Coherent and Incoherent Structures of Noise of Aero-dynamic Origin, TTF-14,091, NASA, Washington, D.C., 1971.
Definitions and Procedure for Computing the Perceived Noise Level for Aircraft Noise,SAE AIR 865A, Aug. 15, 1969.
Doming, A. F., Noise From Propellers With Symmetrical Sections at Zero BladeAngle. NACA TN 605. National Advisory Committee for Aeronautics, Washington,1). C., July 1937.
Deming, A. F., Noise From Propellers with Symmetrical Sections at Zero BladeAngle, II, NACA TN 679, National Advisory Committee for Aeronautics, Washington,D.C.
160
D1.-r.ing, A. F., Prpe•ir Roatation Noise Due to Torque and Thrust, NACA TN 747,Nanlonal Adviliory (orr.mittee for Aeronautics, Washington, D.C., January, 1940.
Denning, R. M., "Propulsion .for V/STOL," Presented at the British Air Line Pilots"I'L.chnacal Symposium, London, Nov. 1970, GP1006.
De~partment of Transportation, "Transportation Noise and Its Control," PB-213-007,June 1972.
Dickerson, D.O., et.al., Transportation Noise Pollution, Control and Abatement,
.NASA Contract NGT 47-003-028, 1970.
i)iprose, K.V., Some Propeller Noise Calculations Showing the Effect of Thickness andPlanform. Technical Note No. M.S. 19, Royal Aircraft Establishment, Farnborough,
England.
Doak, P. E., "Acoustic Radiation form a Turbulent Fluid Containing Foreign lodies,"Proceedings of the Royal Society (London), Vol. A254, pp. 129-145, 1960.
Doak, P. E., and Vaidya, P. G., "A Note on the Relative Importance of Diserete Freq-uency and Broad-Band Noise Generating Mechanisms in Axial Fans," J. of Aound andVibration , Vol. 9, No. 2, pp. 192-196, 1969.
Dodd, K. N. and Roper, G. M., "A Deuce Programme for Propeller Noise '.Jculations,"Royal Aircraft Establishment Technical Note No. M.S. 45, January 1958.
Dodson, A. D., "An lnvesAgation Into Rotor Rotational Noise of Helicopters in the Singleand Tandem Rotor Configuration," M.S.C. Thesis, University of Southampton, England,1969.
Dunn, D. G. and Peart, N.A., Aircraft Noise Source and Contour Estimation, CR-114649, NASA, Washington, 15.-C., 1973.
Eastman, S. E., "Comparative Cost and Capacity Eitimates of Vertiports and Airports1975-1985," ALAA Paper No. 69-208, February 1969.
Eatock, H. L., Plucinsky, J.C., and Saiatsbury, J.A., "Designing Small Gas TurbineEngines for Low Noise and Clean Exhaust," Paper No. 73-1154 presented at the CASI/
ALYA Aeroraautical Meet.!ng, October 1973.
161
!-:dgc, P.M., Chambers, It. M. , and Ilubbard, H.H. , "Evaluation of Measures ofAircraft Noise", Preceedings of NASA Aircraft Safety and Operating Problems
Coa.ervncc, NASA SP-270, Volume 1, 1971.
Einsweiler, R.C., "Planning for Compatibility of Aircraft and Environment," Proceed-ings of the SAEiDO)T Conference on Aircraft and the Environment, WashingtonD.C.,
1971.
Elias, f., et. al. A Study of Turbo-Engine Compressor Noise Suppression Techniques,
NASA CR 1056, Washington, D.C., 1968.
Ernsthausen, W., "Influence of Aerodynamic Characteristics on the Solnd Field and
Radiated Power of an Airserew," Akustieshe Zeitschrift, Vol. 6, pp. 245-261, 1941.
Einsthausen, W., The Source of Propeller Noise. NASA CR 1056, Washington, D.C.,.May 1937.
Evans, T.D. and Nettles, W.E., "Flight Test Noise Measurements of a U-IB Hellei-copter," Paper presented at the AlfS/UTA Joint Symposium on Environmental Effectson ITTOL Designs, Arlington, Texas, November 1970.
Ffowcs Williams, J. E., and Hawkins, D. L., "Theozy Relating to the Noise of Rotat-
ing Machinery," J, of Sound and Vibration, Vol. 10, No. 1, pp. 10-21, July 1969.
Fidell, S., et. al., "The Noisiness of Impulsive Sounds," J. of the Acoustical Societyof America, Vol. 48, No. 6, pp. 1304-1310, 1970.
Fidell, S., and Pearsons, K.S., Study of the Audibility of lJiipulsive Sounds, NASACR-1598, Washington, D.C., 1970.
le Filieul, N. S., "A Study of the Origin and Means of Reducing Helicopter Noise," -
J. of Sound and Vibration, Vol. 3, pp. 147-165, 1966.
Filotas, L.T., "Approximate Transfer Functions for Large Aspect Ratio Wings InTurbulent Flow," J. of Aircraft, Vol. 3, pp. 395-400, 1971.
Filotas, :. T., Theory of At1 ,oil Response in a Gusty Atmosphere Part II - Responseto Discrete Gusts of Continuous Turbulence, Report 141, University of Torontoinstitute for Aturospacv' Studles, Canada, 1969.
Filotaw, L T., "Vortex Induced Helicopter Blade Loads and Noise,'"J.. of Sound andVibration , Vol. 27, No. 3, pp, 387-398, 1973..
162
Fink, M. R., Predicted Noise Decay of Transonic Compressors with Sharp LeadingEdges, Repoit No. I:AR-2173, United Aircraft Research Laboratorties, East Hartford,Conn., 1970.
Fis-'k, W.S. "Creation of Pseudo-Pure Tones and Sensitivity of TPNL to Tolerances onNoise Spectra or Level of Background Noise", Memorandum of November 20, 1967 toMember of SAE committee A. 21 from W R. Morgan.
Flemming, D.M., and Scholten, I., "Noise Problems of VTOL with Particular Refer-ence to the Dornier DO 31," The J. of the Royal Aeronautical Society, Vol. 73, Aug.1969.
Fr ;1en, P.A., Kerwin Jr., E. M., and the staff of Bolt, Beranek and Newman, InC-.,Methods of Flight Vehicle Noihe Predictiorn. WADC Tech. Rept. 58-343, Wright AirDevelopment Center, Wright-iPaterson Air Force Base, Ohio.
Fricke, F.RL., and ".-evenson, D.C., "Pressure Fluctuations in a Separated FlowRegion," J. of the Acoustical .ociety of America , Vol. 44, pp. 1189. 1968.
Gach, M., "Appraisal of Community Response to Aircraft Noise," Proceedings ofthe SAE/DOT Conference on Aircraft and the Environment, Washington, D.C., Feb.1971.
Galloway, W. J., "Noise Exposure Forecasts as Indicators of Community Response,"Proceedings of the &AE/DOT Conference on Aircraft and the EnviroaŽ.ent, Washington,D.C., February [971.
Galloway, W. J., and Bishop, E. E., Noise Exposure Forecast, Evolution, Evaluaon.LExtentions, and Land Use Ir.'erpretations, FAA-NO-70-9, Federal Aviation Auminlstra-tion,-Washlngton, D.C., 1970.
Galloway, W. .. , and von .iferke, H.E., "Individual and Community Reaction to Air-craft Noise; Present Status and Standardization Efforts", Committee No. 4 Report,International Conference on Reduction of Noise and Disturbance of Cival Aircraft,London, November 1966.
Garrett, R.M., "Determination of the Loudness of Repeated Pulses of Noise," J. otSound and Vihr;'tion, Vol. 2, No. 1, pp. 42-52, 1965.
Garrick, I. E., Watkins, C. E., A 'l'hcore'tical Study of the Effect of Forward Speed onthe Free-Space Sound- Pressure Field Around l'rop,4lers. U.eport 1198. NationalAdvisory CommIltce for Acronz'uties, Washington, D.C., August 31, 1953.
163
.. . ..... ... .. Z = .. .. .........l ,.. . . .. ... : • 2
utch-an, J. R., The M .,an•s, of F'recasting the Community Noise Impact of a Trans-portation System, A)-73•6-4, The ... d Corporation, 1971.
6t-or'ge Washirgton U;nivrsity, &)cial Impacts of Civil Aviation ;ýr..d Impleatftons for.u P~olicy (CA1__.. LA)T "iST-10-6, and NASA CR-1988, Washington, D.C., 1971.
fIcrent, H.P., Kuinasaka, 1i. A., and Roundhill, J. P., "Core Engine Noise." Paper7-1027, Am.rican Institute of Aeronautics and Astruna'ltics, October 1973.
Guldt:nherg, S.A., &ad Pelven, V. S., "The Influence of Pressure on Rate of FlamePropagation In Turbulent F'low," 7th, Sympodium Combustion, London, England, pp.590-59.t, 195g.
G raham, J. B., "ltow to Estimate Fan Noise," Sound and Vibration Vol. 6, pp. 24-27,May 1972.
Grande, E., "Core Engine Noise," Paper 73-1026, American institute of Aerorauticeand Astronautics, October 1973.
Green, D. M., "Psychophysical Comparison Mehtods", Transportation Noises,University of Washington Press, 1970.
Gutin, L. J. On the Sound Field of a Rotating Propeller. Physikallsche Zeftschrlftdet sowjetunton. Vol. 9, No. i, 1936. Presented as ARC paper 3115 or HACA Tech.Memo 1195.
164
____________________ 1 -P -- q---
iafrin'r, I., "Sympxosiurn on the Noise and Loading Actions on Helicoptcr, V/STOLAircr 61t, anc Grouad Effect Machines", J of Sound and Vibration Vol. 3, p. 336-339,
Ilalwcv,, I). It., "Flight Operations to Minimize Noise", Vertiflit., February 1571.
Halwvs, I). P. and Cox, C. It., "Noise Reduction Possibilities for a Light Helicopter",S;k' Paper 6ti06,3, October 00l;9.
Hanson, !). B., "Measurements of Static Itlet Turbulence", H'amllton Standard
Engiieering ReUport 6554, May 1974.
Ilargest, T.J. , "V"'s ;I. Aircraft Nolce, lFluid n•n'imia of Rotor a; J Fan Supported
Aircraft at Subsonic Speeds", AGAiRD CP 22, Paris, France, September 1957.
Itartinen, It. and Badgiey, P., R., Model 301 IPLH/ATC Transmission Noise Reductionogram, Report aac Contract i)AAjOI-71-C-0840, U.S. ;Nrin' Aviation Material
Laboratories, Fort Fustis, Va. , 1973.
Hazard, W. I., "Predictions of Noise Disturbance Near U.rge Airports", J of Soundand Vibration, Vol. 15, No. 4, 1971
liealy, G. J., Investigation of V'copellcr Vortex Noise including the Effects of BoundaryLayer Control. CALAC Report 23329, November 1970
Ilealy, G. J., Prediction of Rotor/Propuller Rotational Noised Lockheed Report
LR21206, June 1968,
Ilealy, G. J., Prodi'.tion of Rotor/Propeller Rotational Noise-Nor.dimensional
Parameters, Lockhe.d Report L1122200, March-1969,
ilealy, G. J., "Prwpeller/Rotor Rotatinal Noise Analysis Including Time -Vorying
Blade Forces," Paper FF5, 76th Meeting of Acoustical Society of America, November18-22, 1968.
Ilecker, M ii. L. and Dryter, K. D., Comparisons Between Subjective Ratings ofAircraft Noise and Various Objection MeL4ures, FAA NO-68-33, Federal Aviation
Administration, Washington, D.C.
Ifeller, Hi. and Wilihll, S. E., Thn. tlme (if F) tietuatlmi Forces in the Ger.r-.rtton ofCompressor Noiav Cli 2012, NASA, Washihgton, D.C., 1972
ilcrah, A. S., Acous.tic and Aerodynamic Investtition of Leading-Edge Serra.tions
on iAftLng Suarface, Holt Beranek & Newman, 1971.
165
lhirsh, A. S. andl liyouen, it. E., Aerodrynamni' Noise from Airfoils With and With-out l.,adling ,dge Sc-rations, lReport 2095, Bolt, Berauek, and Newman, Cambridge,
N:a:;sa•ehuswtts, 1971.
Ilildchrand, It. W., vt. al.. Small Turbine Engine Noise Reduction, Vol. I - VI,
AFAPL-TR-73-79, Air Force Aero Propulsion Laboratory, Wright-Patterson AirYomrt! Base, Ohio, 1973.
Hlilurn, 1l. A., iIendersoIa, I1. R., and Pegg, R. J., Ground Noise MeasurementsDluring Flyover, hlover, Landings, and Take-Off Operations of a Standard and a
Modif•ed III[-4t:;B i, lieopter, TM X-2221;, NASA, Washington, D.C., 1971.
Ilhnterheuser, E. G., "Synthesis of Aircrfft Noise", Progress of NASA ResearchRelating to Noise Alleviation of Large Subsonic Jet Aircraft, pp. 537-545, 1968.
lliatcrkeuser, E. G. and Stcrnfeld, H., Civil Helicopter Noise Assessment Study-_Boeing Vertol Model 347, NASA CR- 132420, Washington, D.C., 1974.
llinterkeuser, E. G. ai]d Sternfeld, If., Subjective Response to Synthesized FlightNoise Signatures of Several Types of V/STOL Aircraft. NASA CR- 1118, Washington,D.C., 1968.
IHirsh, N. B. and Ferris, It. W. ,"Design Requirements for a Quiet Helicopter", Paperpresented at the 78th Annual National Forum of the American Helicopter Society,
Washington, D.C., May 1972.
lb, P. Y. and Tedrick. R. N., "Combustion Noise Prediction Techniques for Small
Gas Turbine Engines", Proceedings of Inter-Noise 72 pp 507-512, 1972.
Hoffman, J. 1). and Ve!hoff, H.R., "Vortex Flow Over Helicopter Potor Tips", J of
Aircraft Vol. 8, pp. 739-740, 1971.
Horlock, J. I., "Fluctuating Lift Forces on Aerofoils Moving through Transverse andChordivise Gusts", J of Basic Engineering: Transactions of the American Society ofMechanical Engineers (Series D , Vol. 90, pp. 494-500, 1968.
Hlosier, R. N., Ramakrishman, R., and Pegg, R. J., "The Prediction of Rotor* Rotational Noise Using Measured Fluctuating Blade Loads", Presented at the 30th
Annual National Forum of the American Helicopter Society, May 1974.
Howes, W. L., Loudness Determined by Power Summation, TM X-2300, NASA,Washington, D.C., 1971
Howes, W. L., Relations Among Loudness, Loudness Level. and SPL. TM X-2298,
NASA, Washington, D.C., 1971.
166
.v.
"lubbard, II. 11. Proptcller-Noise Charts for Transport Airplanes. NACA TN296'. National Advisory Committee for Aeronautics, Washington, D.C.
V1 Hubbard, I1. Ht., l.ansing, D. L., and Runyan, H. L., "A Review of Rotating Bladeoil.Technology", Loughborough University of Technology, Symposium on Aerodynamic
$.- Noise, Loughborough, England, September 14-17, 1970.
"*!. lHubbard, I1. If. and Maglieri, D. J., "Noise Characteristics of Helicopter Rotorsat Tip Speeds Up to 900 Feet Per Second", J of the Acoustical Society of America,Vol. 32, No. 9, September 1960.
"Hubbard, It. It., Regier, A. A., Free-Space Oscillating Pressures Near the Tipsof Rotating Propellers. NACA Report 996, National Advisory Committee forAeronautics, Washington, D.C.
SlHubbard, if. It. and Regier, A. A., Propeller Loudness Charts for Light Airplanes,T. N. No. 1358, National Adviaory Committee for Aeronautics, Washington, D.C.,
July 1947.
p.- Huff, R. G., Clark, B. J. and Dorsch, R. G., Interim Prediction Method for LowFrequency Care Engine Noise, rM X-71627, NASA, Washington, D. C., 1974
Hulse, B., et. al., Some Effects of Blade Charactei-stics on Compressor NoiseLevel, FA65WA-1263, Federal Aviation Administration, Washington, D.C., 1966.
"Hulse, B. T., and Large, J. B., "The Mechanisms of Noise Generation in aCompressor Model", Paper 66-6T/N 42, March 13-17, 1966, meeting presented atthe ASME.
'I
Hunting, A.W. and Fleming, R.S., Helicopter Steep Angle GCA Approach Evaluation,i€ Project Report AD676528, Federal Aviation Administration, Washington, D.C, 1968.
Hurlburt, R. L., "Noise in an Airport Community", Proceedings of Inter-Noise 72,pp. 366-371, 1972.
ICAO, Report of the Special Meeting on Aircraft Noise in the Vicinity of Aerodromes,Document 8857, inteniational Civil Aviation Organization, 1969.
Jagger, D. H. and Kemp, E.D.G., "The Potential and Development of a V/STOLInter-City Airliner", Aircraft Engineering, January 1970.
167
m~~. . . . . --- **. .. . .. . . .
.Johnson, I1. K., Ikevtlupment of a rechni, ue for Realistic Prediction and ElectronicS% nthtsis of Ifelicopter Rotor Noise, TR 73-8, U.S. Army Air Mobile by Research-ind D)cvclopment Laboratory, Fort Eustis, Va., 1973.
Johnson, If. K. and Katz, W. M., Investigation of the Vortex Noise Produced by aIklicopter Rotor, Rochester Applied Science Associates, USAAMRDL TR 72-2,February 1972.
.]ohnston, G. W., "Fan/Rotor Noise - Some Recent Developments", Presented at theCASI/AIAA meeting, October 29, 1973.
.Johnston, G. W., V/STOL Community Annoyance Due to Noise, Technical Note No.177, University of Toronto Institute for Aerospace Studies, Canada, 1972.
•Jonsson, E. and Sorenson, S., "Adaptation to Community Noise - A Case Study",J. of Sound and Vibration, Vol. 26, No. 4, 1973.
Koramcheti, K. and Yu, Y. H., "Aerodynamic Design of a Rotor Blade for MinimumNoise Radiation", AIAA Paper No. 74-571, Presented at the Fluid and PlasmaDynamics Conference, June 17 - 19, 1974.
Kazin, S.B. and Emmerling, J.J., "Low Frequency Core Engine Noise", Paper 74-WA/Aero-2, American Society cf Mechanical Engineer, 1974.
Kazin, S. B., et. al., Core Engine Noise Control Program (3 Volumes), Report No.DOT-FA72WA-3023, Federal Aviation Administration, Washington, D.C., 1975.
Keefe, R. T., An Investigation of the Fluctuating Forces Acting on a Stationary CircularCylinder in a Subsonic Stream and of the Associated Sound Field, UTIA Report No. 76,University of Toronto, Canada, 1961.
Kelly, J. C., "Broadband Fan Noise Due to Vortex Shedding", Note No. RR (OH) 400,Rolls-Royce Limited, Englapd, 1969.
Kemp, N. H., "On the Lift and Circulation of Airfoils in Some Unsteady Flow Problems",J. of the Aeronautical Sciences, Vol. 19, pp. '13-714, 1952.
Kemp, N., Arnoldi, R. A., Machine Calculation of Free-Space Sound Pressure FieldAround Propellers in Forward Motion. Report RB-22673-1, United Aircraft CorporationResearch D--partment, East Hartford, Connecticut. February 1954.
Kemp, N. H. and Sears, W. R., "The Unsteady Forces Due to Viscous Wakes InTurbornachinery," J. of the Aeronautical Sciences, July 1955.
168
Kester, .1.1). "'Sourcs of .Nise f•ri,' Advanvcd Turbofan Engines," Prepared forSpring 196s4 AS.MI: Alecting.
King, I,., l' 1:1(iction of Tai i ulor Noi.c, Te,-hnical Report AMTR-11, SikorskyAircraft, Strptford, C..nn., Noveniber, 1970.
King, It.1 and Sthlegt'l, it. ".'e*di-ticn Methods and Trends for Helicopter RotorNoise" Procecdingi of tne Third ('AI, AVI.ABS Symposium, Aerodynamics of RotaryWing and v.STrO1 A ire raft, J1 une I9 ;.
Knowler, A. E., "The St.cond N.'oi.ec and Social iurvey Around Heathrow London Air-port", Proceedings of the 7th Intcra-mtional C,'rgress on Acoustics, Volume 2,(A73-12951 03-12) Budapest, Ak.-'Ic nias.Kiado, 1971.
Koch, W., "On the TIa'an:;!i,;:-ion of Sound Waves Through a Blade Row," J. of Soundant: Vibration, Vol. is, No. 1, pp. 111-128, 1971.
Kramer, M., "Thu Aerodynarni. Protile as Acejstic Noise Generator," J ofAeronautical Science Vol. 20, pp 280-282, 1953.
Krejsa, E.A. andVelerno, M. F., Interim Prediction -Method for Turbine Noise,Proposed NASA TM, Washington, D.C.
Fryter, K. D., "A Note on the Quantity (Effective) Perceived Noisiness and Units ofPerceived.Noise Level", J. of Sound and Vibration, Vol. 25, No. 3, 1972
Kryter, K. D., "Concepts of Pcerceived Noisiness, Their Implementation and Appli-cation," J. of the'Acoustical Society of America. Vol 43, pp. 344-361, 1968.
Kryter, K. D., "Possible Modifications to the Calculation of Perceived Noisiness",CR-1636, NASA, Washington, D.C., 1970.
Kryter, K. D., " Prediction of Effects of Noise on Man", Progress of NASA Research7 Relating to Noise Alleviation of Large Subsonic Jet A4rcraft, SP--189, NASA,
Washington, D.C., 1968.
Kryter, K. D., .Review of Research and Methods for Measuring the Loudness andNoisiness of Complex Sounds, CR-422, NASA, Washington, D.C., Apri! 1966.
Kryter, K. D., "Scaling Human Reactions to the Sound from Aircraft," J. AcousticalSociety of America, Vol. 31, No. 11, pp 1415-1429, 1959.
Kryter, K.D., Johnson, I'.J., and Young, J.R., Judgement Tests of Flyover Noisefrom Various Aircraft, CR-1635, NASA, Washington, D.C., 1970
169
Kryter, K.D. and Pearsons, K.S., "Judged Noisiness of a Band of Random NoiseContaining an Audible Pure Tone", J. of the Acoustical Society America, pp. 138-150,19(;6.
Kryter, K. D. and Pearsons, K.S., "Some Effects of Spectral Content and Durationon Perceived Noise Level", J. of the Acoustical Society of America, Vol. 35, No. 6,pp. 866-883, 1963.
Kr%'ter, D. K. and Williams, C. E., Some Factors Influencing Human Response to Air-craft Noise, FAA-AI)S-42, Fe'deral Aviation Administration, Washington, D.C., June1965.
Krzy•oblocki, M.A., "Investigation of the Wing-Wake Frequency With Application ofthe Strouhal Number," J. of the Aeronautical Sciences, Vol. 12, January 1945.
Kurbjun, M. C., Vogelcy, A. W., Measurements of Free-Space Oscillating PressuresNear Propellers at Flight Mach Numbers to 0. 72. Report 1377. National AdvisoryCommittee for Aeronautics, Washington, D.C., 1958.
Landgrebe, A. J., "The Wake Geometry of a Hoverning Helicopter Rotor and itsInfluence on Rotor Performance", Paper presented at the 28th Annual Material Forumof the American Helicopter Society, May 1972.
Laskin, I., Orcutt, F. K., and Shipley, E. E., Analysis of Noise Generated by UH-1Helicopter Transmission, TR 68-41, U.S. Army Aviation Material Laboratories,Fort Eustis, Va., 1968.
Leverton, J. W., "Helicopter Noise." Institute of Sound and Vibration ResearchMemorandum No. 167., 1967.
Leverton, J. W., Helicopter Noise-Blade Slap, Part I - Review and Theoretical Study.NASA CR-1221, Washington, D.C., -1968.
Leverton, J. W., Helicopter Noise - Blade Slap Part H1 Experimental Results, NASACR 1983, Washington, D. C., 1972.
Leverton, J.W., "Helicopter Noise-Are Existing Methods Adequate For RatingAnnoyance or Loudness?". , J. of the American Helicopter Society, April, 1974.
Leverton, J.W., "The Noise Characteristics of a Large 'Clean' Rotor", AGARD-CP-111, Conference Proceedings No. III on Aerodynamics of Rotary Wings, 1972,also J. of Sound and Vibration, Vol. 27, No. 2. pp. 357-376, 1973.
170
Leverton, J.W. and Pollard, J.S., "A Comparison of the Overall and BroadbandNoise Characteristics of Full-Scale :and Model Helicopter Rotors", J. of Sound andVibration, Vol. :30, No. 2, pp 135-152, 1973.
Leverton, J.W., and Taylor, F.W., "'Helicopter Blade Slap." J. of Sound andVibration, Vol. 4, p. 345-357, 1%6.
Levi, H. and Forsdyke, A.G., "Steady Motion and Stability of a Helical Vortex",Proceedings of the Royal Society of London A, Vol. 120, pp. 670-690, 1928.
Lighthill, M.J., "Sound Generated Aerod*'vnrmically". Proceedings of the RoyalSociety, London, England. A21I. 1952.
Lighthil, M.J., "Sound Generate'd Aerodynamically, Bakerian Lecture 1961,"Procedings of the Royal Society , London, England Vol. 267, p. 147-182, 1962.
Little, J.W., "Human Response to Jet Engine Noises", Noise Control, Vol. II,pp 11-13, 1961.
Little, J.W., and Mabry, J. E., "Sound Duration and Its Effect on Judged Annoyance".J. of Sound and Vibration, Vol. 9, pp 247, 1969.
Lockheed Aircraft, "Improved Rotor/Propeller Noise Predicting Techniques," Dec.29, 1969, Indeper.dent Reaearch Engineering Work Assignment 41-5487-7346 CALAC.
Loewv', R.G., "Aural Detection of Helicopters in Tactical Situations," J. of theAmerican Helicopter Society, Vol. 8, No. 4, Oct. 1963.
Loewy, R. G. and Sutton, L. R., A Theory for Predicting the Rotational Noise ofLifting Rotors in Forward Flight, Including a Comparison With ExperimentUSAAVLABS Tech. Report 65-82, U.S. Army Aviation Material Lilboratories, FortEustis, Va., 1966. -
Lowson, M. V., "Basic Mechanism of Noise Generation by Helicopters, V/STOL Air-craft and Ground Effect Mechanisms," J. of Sound and Vibration, Vol. 3, No. 3. pp.454-466, 1966.
Lowson, M. V., "Compressor Noise Analysis," NASA SP-189, Washington, D. C.,October 1968.
Lowson, M.V., "Fundamental Considerations of Noise Radiation by Rotary Wings",AGARD Conference Proceedings No. 111 on Aerodynamics of Rotary Wings, September,1972.
171
Lowson, M. V., "Possible Mechanism loi the Surface-?Pressure Fluctuations BeneathTurbulent Boundary Layers," J. of the Acoustical Society of America, Vol. 40,
pp. 1264, 1966.
Lowson, M. V., "Reduction of Compressor Noise Radiation," J. of the Acousticalsociety of America, Vol. 43 No. 1, pp. 37-50, January 1968.
Lowson, M. V., "Rotor Noise Radiation in Non-Uniform Flow." Paper presented atthe Symposium on Aerodynamic Noise, Loughborough University of Technology. 1970.
Lowso\ , M.V., "Theoretical Analysis of Compressor Noise," j. of the AcoustialSociety of America, Vol. 47, No. I (Pt. 2), pp. 371-385, January 1970.
Lowson, NI. V., "The Sound Field for Singularities in Motion. "roceedings of theRoyal Aeronautical Society, Vol. 286, pp. 559-572, August 1965.
Lowson, M. V., Thoughts on Broad Band Noise Radiation by a Hel iopter, *Wyle
Laboratories Report WR 68-20, December 1968.
Lowson, M. V. and J. B. Ollerhead, "A Theoretical Study of Helicopter Rotor Noise,"J. of Sound and Vibration, Vol. 9, No. 2. March 1969.
Lowson, M.V., Oilerhead, J.B.; "Problems of Helicopter Noise Estimation and-Re-duction," AIAA Paper 69-195, February 1969.
Lowson, M. V. and J. B. Ollerhead, Studies of Helicopter Rotor Noise, Tech. Rept.68-60, AD684394, USAAVLABS. January 1969.
Lows on, M. V., Whatmore, A., and Whitfield, C. F., Source Mechanisma for RotorNoise Radiation, Report TT7202, Loughborough University of Technology, England,
1972.
Lyon, R. H., "Radiation o. Noise by Aerofoils That Accelerate Near the Speed of Sound".J. of the Acoustical Society of America, Vol. 49, No., pp. 894-905, 1971.
Lyon, R. H., Mark, W. D. and Pyle, R.W. ,Jr., "Synthesis of Helicopter Rotor Tipsfor Less Noise," J. of the Acoustical Society of America, Vol. 53, No. 2, pp 607-618, 1973.
Macfarlane, C. G., "On the Energy-Spectrnm of an Almost Periodic Succession of
P-ulses," Proceedings of the I. R. E. . October 0-49.
Magee, J.P., Maisel, M.D., and Davenport, :..,.. "rh u i gi. anti perforz•ancc
Prediction of Propeller/Rotor for VTOL Applications", Paper No. 325, presentedat the 25th Annual Nation Forum of the Amcrip.an Helicopter Society, Washington,
D.C., June 1970.
172
Miglicri, I). J., lHilton, 1). A. and Hubbard, if. If., Noise Considerations in the Designand ()pcrations of V/ST)I Air'raft, NASA TN D-736, Washington, D.C., 1961.
Magliozzi, B. and Ghanger, T. G., Advanced V/STOL Propeller Technology - Far FieldN.)ise. Investigation, AIFI)I.-TR-71-s)5, Vol. 13, 1971.
Mani, R., "Noise Due to Interaction of Inlet Turbulence with Isolated Stators andRotor", J. of Sound and Vibration, Vol. 17, pp. 251-260, 1971.
Marshall, D.A.A., "Sources of Noise in Acro-Engines", Paper presented at the firstInternational Symposium on Air-Breathing Engines, 1971.
M:, rtc, J. E., and Kurtz, D.W., A Review of Aerodynamic Noise from Propellers,
Rotors, and Lift Fans, NASA TiH 32-146i2, Washington, D.C., 1970.
M:athews, I). C. and Peracchio, A. A., "Progress in COre Engine and Turbine NoiseTechnolagy", Paper No. 74-948, American Institute of Aeronautics and Astronautics,August 1974.
McCann, J. C. and Sofrin, T. G., "Pratt & Whitr.ey Aircraft Experience In CompressorNoise Reduction," Acoustical Society of America, Paper 202, November 1966.
McCormick, B.W., Jr. and Surendraiah, M., "A Study of Rotor Blade - Vortex In-teraction", Paper No. 421, Presented at the 26th Annual National Forum of theAmerican Helicopter Society, Washington, 1). C., June 1970.
McPike, A. L., "Recommended Practices for Use in the Measurement and Evaluationof Aircraft Neighborhood Noise Levels," Preprint 65-216 SAE, 1965.
Metzger, F. B., et. al., A Study of Propeller Noise Research, SP 67148, Rev. A,Hamilton Standard, Windsor Locks, Conn. 1961.
Meyer, J. R. and Falabella; G.-,-An Investigation of the Experimental AerodynamicLoading on a Model Ifelicopter Blade, TN-2953, National Advisory Committee forAeronautics, Washington, D.C., 1953.
Miller, L. M. and Ver, I. L., Noise Study in Manhattan, New York City for the Eva!u-ation of Dominant Noise Sources including Helicopter Traffic, Report No. 1610, BoltBeranek and Newman, Cambridge, Mass., 1967.
Miller, R. II., "'otor Bllade Harmonic Airloading", .J. of ,he American !nstitute ofAeronautics and AM.tronpautlcs, Vol. 2, No. 3, 1964.
173
?.iilh'r, It. 11., "Unstad., Airloads on Illicopte," Rotor Blades", J. of the Royal
Aeronaut cal Socit.tv, Fol. 6.s, No. 6;40, 196-1.
\Miller, It. It., "Notes or. Cost of Noise Reduction in Rotor/Prop Aircraft," Conference
un V ST'OI Noise Generation and Suppression, MIT Memo Report FTL-M68-9,Cambridge, Mass. , August 196S.
Miller, L. N. and Beranek, L. L., "Attenuation of Sound Passing from Outdoors into
A Tvpical House," J. of the Acousticl Society of America, Vol. 29, pp 1169-1179,1957.
Monnerie, B. and Tognet, A., "Study of the Effect of the Ma±eginal Vortex from aIfulicopter Blade on the Aerodynamic Flow Around the Following Blade (Etude del'Influ,:nce du Tourbillon Marginal Issue d'une Pale d'lielicoptere sur lEcoulementAerodynamiqf.' Autour de la Pale SuivanteV', Paper presented at the AssociationF!.r'ncakise des Ingenieurs et Techniciens de l'Aeronautigue et de l'Espace, Colloguecd'Acrodyi.amique Appliquee, 7th, Modane, Savoie and Ecole Centrale Lyonnaise,Ecully, Rhone, France, Nov. 4-6, 1970.
Morfey, C. L., "A Review of the Sound-Generating Mechanisms in Aircraft-EngineFans and Compressors," Aerodvnamic Noise, pp. 299-329, H.S. Ribner, Ed., Toronto,Canada, 1969.
Morfey, C. L., "Broadband Sound Radiated from Subsonic Rotors", InternationalSymposium on the Fluid Mechanics and Design of Turbomachinery, PennsylvaniaState University, 1970.
Morfey, C. L., "Lift Fluctuations Associated With Unsteady Chordwise Flow Paston Airfoil," J. of Basic Engineering: Transactions of the American Society ofMechanical Engineer (Series 1)), Vol. 92, pp. 663-665.
Morfey, C. L., "Rotating Blades and Aerodynamic Sound." J. of Sound and Vibration,Vol., 2-, pp. 587-4617. 1973.
Morfey, C. L., "Sound Generation in Subsonic Turbomachinery," Transacti6n of theASME, Series D., Journal of Basic Engineering, Vol. 92, pp. 450-458, 1970.
Morfey, C. L., "The Sound Field of Souices in Motion." J. of Sound and VibrationiVol. 23, pp. 291-295. 1972
Morfey, C. L., "Tone Radiation from an Isolated Subsonic Rotor," J. of the AcousticalSociety of America, Vol. 49, pp. 1690-1692, 1971.
Moreira, N. N1. and Bryan, M. E., "Noise Annoyance Susceptibility", J. of Sound andVibration, Vol. 21, No. 4, 449-462, 1972.
174
Morse, P.M. , and Ingard, K. V. , TheoreticLl Acoustics, McGraw-Hill, New York,
Motsinger, R., Prediction of Engine Combustor Noise and Correlation With T-64Engine Low Frequency Noise', R72AEG:113, General Electric Company, 1972.
Mugridge, B. D., "Acoustic Radiation from Acrofoils With Turbulent Boundary Layers."J. of Sound and Vibration, Vol. 16, pp. 5!)3-614, 1971.
Mugridge, B. D., "Broadband Noise Generation by Aerofoils and Axial Flow Fans",paper 73-10111, presented at the AIAA Aerocoustics Conference, October 15-17, 1973.
Mugridge, B. I)., "Sound Radiation from Aurofoils in Turbulent Flow," J. of Soundand Vibration, Vol. 13, pp. 3:62-363, 19j70.
Mull, H. R., External Noise Characteristics of Two Commercial Transport Helicopters,United Acoustic Consultant Report R-6-12, Haarold R. Mull and Associates, Wilton,Conn., 1964.
Mull, H. R., Washington D. C. Hiclicopter Demonstration, Report R-6606, Harold R.Mull and Associates "'ilton, Conn., 1969
Muller, J.L., "Calculation of Aircraft Noise Duration", J. of Sound aid Vibration!Vol. 16, No. 4, 11971.
Malil-r, E.A. and Okermeler, F., "The Spinning Vortices as a E-.,urce of Sound,"AG:ARD CP 22, Paris, France, Sept. 1967.
Munch, C.L., Theoretical Helicopter Noise Prediction Including Comparison WithExperiment, Wyle Laboratories Research Staff Report WR 69-18, August 1969.
Munch, C.-L. Simplified Helicopter Rotor Noise Prediction Program. TechnicalReport AMTR-9, Sikosky Aircraft, Stratford, Conn., November 1970.
Munch, C. L., Standard Far-Field S-65 Rotor and Aircraft Noise Snetra Teclnic-alReport ETR-2, Sikosky Aircraft, Stratford, Conn., March 1971.
Munch, C.L., Predictions of V/STOL Noise for Application to Community NoiseExposure. Report No. ID)'T-'rSC-OST-73-19. Department of Transportation,Washingtton, 1). C.
Munch, C. L. and King, R.J., Com.tmunityAvcvptance of Helicopter Noise: Criteriaand Applicationt NASA CR-132.130, Washington, 1). C., 1974.
175
:ig.l, 1). tC., Parnmll, J. [. ond Parry, Ii. J., "Procedure for CorrectingPorcuivcd Nuisc Level fio the E.ffect of Background Noise", Transportation Noises'University of Washington Press, 1970.
NASA Contract NASI-12505 - iUsearch Program to Study the Effects of At.mosphericlurbulence oil Rotor Generate Noise. June 1973.
NASA Contract NASI-13015 - Research Program to Explore the Influence ofForward Flight on Propeller Noise. May 1974.
National Bureau of Standards, "The Social Impact of Noise", EnvironmentalProtection Agency PB 206 724, December 1971.
Naumann, 11. and Yeh, If., "Lift anti Pressure Fluctuations of a Cambered AirfoilUnder Periodic Gusts and Applications to Turbomachinery", J of Engineering forPower: Transactions of the Americ.n Society of Mechanical Engineers (Series A),Vol. 95, pp 1-10, 1973.
Nemec, J., "Noise of Axial Fans and Compressors: Study of Its Radlatio- andReduction", J of Sound and Vibration. Vol. 6, No. 2, pp. 230-236, 1967.
:Joad, P. J., "Theoretical Prediction of Helicopter Rotor Noise", T. H. G.Note No. 5/63, Westland Aircraft Limited, England, 1963.
Obata, Juichi, Yosida, Yahei, Sakae, Studies on the Sounds Emitted by RevolvingAirscrews. Parts I & 11, Aero. Res. inst., Tokyo Imperial University, Tokyo,Japan. Report No. 79 and 80, Vol. VI, No. 13 and Vol. IV, No. 14, 1932.
O]1-rhead, J. B., Subjective Evaluation of General Aviation Aircraft Noisea FAA-No. 67-35, Federal Aviation Administration, Washington, D. C., 1968.
Ollherhead, J. B., Soine Analyses of Helicopter Noise, WR 68-8, Wyle Laboratories,llur"tsville, Alabama, 1969.
Ollherhead, J. B., Acoustic Considerations in the Design of a Quiet Helicopter,T. R. WR70-3, Wyle Lah-ratoric, Huntsville, Alabama, 1970.
Ollerhead, J. B., "Rotor, Propeller, and Fan Noise in Theory and Practice",L•oughborough University of Technology, Symposium on Aerodynamic Noise,Loughborough, Engl:id, Septermber 14-17, 1970.
OllerheMd, J. B., An Evaluation of Methods for Scaling Aircraft Noise Perception,
CR-1883, NASA, Washington, 1). C., 1971.
Oilerheiad, J. B., lll,'oPtter Aural Detectability, Technical Report 71-33, 1971.
176
Ollcrlhtad, .J. B. , "Scaling Aircraft Noise Perception", J of Sound and Vibration, Vol.2 , No. 3, pp. 361-38, 1973.
ollerhead, J. B. and Lowson, M. V., "Problems of Hfelicopter Noise Estimation andReduction", Paper No. 1;9-195, AIAA, February 17-19, 1959.
olklvrhe.a:', .1. 1P. and Munch, C. L. , An Application of Theory to Axial Comprescor
Noise, C1-1519, NASA, Washington, 1. C. , 1970.
Oilvrheac, J. B. and Tayior, It. B., DUscriIption of Helicopter Rotor NoiseComputer Progrurn USAAV'LAJIS TR 68-1, Fort Eustis, Va., 1969.
Parnell, J. E., Nagle, D. C., and Parry, If. J., Growth of Noisiness for Tonesand Bands of Noise at 1)iifercnt Frequencivs, FAA-DS-67-21, Federal AviationAdministration, Washington, D.C., 1967.
Parry, if. J. and Parry, .1. K., "The Interpretation and Meaning of LaboratoryDeterminations of the Effect oif Duration on the Judged Acceptability of Noise",.I of Sound and Vibration Vol. 20, No. 1, 1972.
Paterson, R. W., et. al., Vortex Shredding Noise of an Isolated Airfoil UnitedAircraft Research Laboratories, Technical Report K910867-6, East Hartford, Conn.1971.
Pearsons, K. S., The Effect of Duration :cnd Background Noise LI vel on PerceivedNoisiness. FAA ADS-7h, Federaltion Aviation Administration, Washington, 1D. C.,April, 1966.
Pearsons, K. S., Noisiness Judgements of Helicopter Flyovers, FAA-DS-67-1,Federal Aviation Administration, Washington, D.C., 1967.
Pearsons, K.S. "As.sessment (f the Vadidity- f Pure Tone Corrections to ReceivedNoise Level", Progess of NASA Research Relating to Noise Alleviations of Large.-Lbsonic -Jet Aircrft. SP-10i, NASA, Washington, D. C., 1968.
Pearsons, K. S., Combination Effects of Tone and Duration Parameters onPerwcivcd Noisiness, NASA, Washington, 1). C., 1969.
Pea rsons, K. S., "Laboratory Studies on the Effects (if Duration and SpectralComplkxixty on i!ibjective Ratings of Nois-", ASIJA Reports No. 4, pp. 228-237,1969.
Pearsons, K.S., Bennett, R. L. and F!rlell, S., "Situdy of Effects of the Doppler
Shift on Perceived Noisiness", Acoustical Society of America, Houston, Texas,
November, 1970.
177
icý, rsons, K.S. and Beunectt, R. L., Handbook of Noise Rating, CR-23 76, NASA,
Washing•,tn, D.C., 1974.
Piarson, R. G. and Hart, F. D., "Studies Relating the Individual Char~ctezistics of
People With Their Responses Wo Noise", Progress of NA•;A Research Relating toN,)ise Allev'iatinn of Large Subsonic Jet Aircraft, SP-189, NASA, Waahington
D.C., 1968.
Pearsons, K.S., Horonjeff, R. D., and Bishop, E. E., The Noisu'iess of TonesPlus Noise CR-1117, NASA, Washington, D.C., 1068.
Pegg, R. J., Henderson, .I. R, and Hilton, D. A., Rcr-z'lts of the Flight NoiseMeasurement Program Using a Standard and M1odfijed SH-3A lielicopter,
TN D-7330, NASA, Washington, D. C., 1973.
Pugg, R. J., Henderson I1. R. and Hiilton, D. A., Flyover Noise Characteristics
of a Tilt-Wing V/STOL Aircraft (XC-142A). TM X-3074, NASA, Washington, D. C.,1974.
Pickett, G. F., "Turbine Noise Due to Turbulence and Temperature Eluctuatlons",
Paper presented at the Zighth International Congress in Acoustics, July 1974.
Piziali, R. A. and DuWaldt, F. A., A Method for Computing Rotary Wing AirloadDistributions in Forward Flight, TR 62-44, U. S. Army Transportation ResearchCommand, Ft. Eustis, Va., 1962.
Pohard, J. S. and Leverton, J. W., "Effect of Blade Tip Planform in the Noiseand Aerodynamics of a Helicopter Rotor", lResearch Paper 414, Westland HelicoptersLimited, Frgland, 1972.
Potter, R. C., An Experiment to Examine the Effect of Porous Trailing Edges onthe Sound Generated by Bladeq in an Ailflow, Report WR 68-_6,-Wyle Laboratories,Huntsville, Ala., 1968.
Powell, A., "Theory ot Vortex Sound", Journal of the Acoustical Society ofAmerica Volume 3#L, Number, 1, January 1964.
Price, P. B., et. al., "Optical Studies of the Generation of Noise in TurbulentFlames", 12th Synpesluni on Combustion, pp. 1093-1101, Poitiers, France, 1968.
Reichardt, W., "Subjective and Objective Measurement of the Loudness Level ofSinwle and Repeated Impulses", J. of the Acoustical Society of America. Vol. 47,
No. 6, pp 1557-1562, 1970.
173
itibre;, H. S., "N,'r'e oi Aircraft", Paper 65-545, UTIAS Rev. 24, InternationalCouncil oi the Aeronautic'l 6cieaces, 4th Congress, Paris, France, Aug. 24-28, 1964.
Wlrce, C. G., and Ztpler, E. " Loudness and Pitch Sensation of an Impulsive Soundof Very Short Duration", .i. of Srund and Vibrator, Vol. 5, No. 2, pp. 285-289, 1967.
Richards, E. J., "Aeronautical Research at Southampton University", Journ-al of
the Royal Aeronautical Society, Vol 69, pp. 505-541, August 1965.
Richardson, E. G., "Aeolian Tonaj', Proceodings (,f the Physical Society ofLndonn, Vol. 36, 1124.
Hlchari3aon, E. G., "Critical Velocity of Flow Past Objects of Airfoil Section",
Procebdings of the Physical Society of London, Vol. 37, 1925.
Rled, W. W., The Statistical Theory of Turbulence, N.,,thwestern University Report
400-41-57, Sept. 1957.
Riedel, S. C. and Schairer, J. 0., "Acoustics Data Obtained from Blade/VortexLnteraction Study", Boeing Vertol Company, Philladelphia, Pa., 1970.
Robinson, D. W. and Bowsher, J. M., "A Subjective Experiment with HelicopterNoises", J. of the f)oyla Aeronautical Society, pp. 335-637, 1961.
Robtnbon, D. W., "The Subjective Basis for Aircraft Noise Limitation", J, fthe Royal Aercnanticai Society. Vol. 71, No. 678, pp. 396-400, June 1667.
Robinson, D. W., The Concept of Noise Pollution Level, National Physics LaboratoryAeronautical Reaort AC 3 1969.
Robinson, D. W., A New Basis for Aircraft Noise Rating, National PhysicsLaboratory Aeronautical Report AC 3i., 1971.
Rushko, A., "Experiments cf the Flow Past a Circular Cylinder at Very HighReynolds Number", J. of Fluid Mechanics Vol. 10, Part 3, 1961.
Ross, D., Vortex Sheddlnig Sounds of Propellers. Report No. 1116, Bolt, Beranek,and Newman, Cambridge, Mass., 1964...
Rule, S. J. and Little, J. W., "Effect of a Composite Instructional Set on Responseto Complex Sounds", .1. of Experimental Psychology. Vol. 71, p. 200, 1966.
Rtylander, It., Sorvnson, S., and Kajland, A., "Annoyance Reaction from AircraftNoise Exposure", &_.,f 'ý)und and Vibration, Vol. 24, No. 4, pp. 419-444, 1972.
179
FRylander, R., Sorensen S., Alexander, A., and Gilbert, Ph., "Determinants forAircraft Noise Annoyance - A Comparison Between French and Scandanavian Data",J. of Sound and Vibration. Vol. 28, No. 1, pp. 15-21, 1973.
Sadler, S. G., "A Method for Predicting Helicopter Wake Geometry, Wake-InducedFlow and Wake Effects on Blade Airloads", Paper presented at the 27th Annual NationalV/STOL forum of the American Helicopter Society, Washington, D. C., May 1971.
Sadler, S. G. and Loewy, A.; A Theory for Predicting the Rotational and Vortex Noiseof Lifting Rotors in Hover and Forward Fli1ht, Rochester Applied Science Associates
r Rept. 68-11, Rochester, N.Y., 1968.
Sadler, S. G., Johnson H. K., and Evans, T. D. , Determination of theAerodynamic
4 Characteristics of Vortex Shedding from Lifting Airfoils for Application to the Analysisof Helicopter Noise, Report 73-02, Rochester Applied Science Associatts, Inc., 1973.
Sadler, S. G. and Loev y, R. G., "The Importance of Vortex Shedding Effects on Hell-copter Rotor Noise with and without Blade Slap," Procedings of the Third CAL/AVLABSSymposium, Vol. 1. June 1969.
SAE, Technique for Developing Noise Exposure Forecasts. FAA-DS-67-14, FederalAviation Administration, Washington, D.C., 1967.
Scheiman, J,: A Tabulation of HelicopterRotor-Blade Differential Pressures, Stresses,and Motions, as Measured In-Flight, NASA TM-X-952, Washington, D.C., 1964.
Scheiman, J., Hilton, D. A., and Shivers, J. P., Acoustical Measurements of the VortexNoise for a Rotating Blade Operating With and Without Its Wake Blown Downstream,TND-6364, NASA, Washington D.C., 1971.
Scheiman, J., and Ludi, L. H., Qualitative Evaluation of the Effect of Helicopter RotorBlade Tip Vortex on Blade Airloads, TND-1637, NASA, Washington D.C., 1963
Schlegel, R. G., Hush Final Report - Quiet Helicopter Program, SER-611878, SikorskyAircraft, Stratford, Conn., 1970. -
Schlegel, R. G., and Bausch, W. E., "Helicopter Rotor Noise Prediction and Control"J. of the American Helicopter Society, Vol 14, No. 3, July 1969.
Schlegel, R. G. and Bausch, Helicopter Rotor Rotational Noise Prediction and Correlation.
USAAVLABS TR 70-1A and 1 B, 1970, U.S. Army Aviation National Laboratories, FortEustis, Va.
Schlegel, R., King, R., and Mull, H., Helicopter Rotor Noise Generation and Propagation.
* Tech. Report 66-4. U. S. Army Aviation Material Laboratorie3, Fort Eustis, Virginia.* f-. October 19615.
180 I
I - Schiegel, R. G. and Mard, K. C., "Transmission Noise Control-Approaches in Helt-•'•copter Design," Paper 67-DE-58, American Society of Mechanical Engineers, 1967.
Schmitz, F. H., et. al., A Comparison of Optimal and Noise - Abatement Trajectoriest. #.,of a Tilt-Rotor Aircraft, CR-2034, NASA' Washington, D.C., 1972.
.Schritz, F.H. and Stepniewski, W. Z., "Reduction of VTOL Operational Noise ThroughFlight Trajectory Management", AIAA Journal of Aircraft, Vol 10, No. 7, July 1973.
Schultz, T. J., Noise Assessment Guidelines and Tecbnical Background, HUD ReportNo. TE/NA-172, 1972.
Sears, W. R. "Some Aspects of Non-Stationary Airfoil Theory and Its Practical Applica-tion," J. of the Aeronautical Sciences, Vol. 8, No. 3, Jan. 1941.
* " Semotan, J. and Semotanova, "Startle and Other Human Responses to Noise", J. of- Sound and Vibration, Vol. 10, No. 3, pp. 480-489, 1969.
* Shahady, P.A., "A Survey of Propeller Noise Prediction Methods", Air Force FlightDynamics Labora~ory, Pres. at Las Vegas Symposium of the Acoustical Society ofAmerica Septembet 1968.
I,I',. Shahady, F.A., etal., "Reduction of Noise from Small Turbo P-ropulsion Engines",
Paper No. 74-59 presented at the AIAA 12th Aerospace Sciences Meeting, January 1974.
Shapiro, N., and Healy, G.J. "A Realistic Assessment of the Vertiport/Community
Noise Problem, "Journal of Aircraft Vol. 5, No. 4, July 1968.
Sharland, I. J., "Sources of Noise in Axial Flow Fans," J. of Sound and Vibration.
Vol. 1, No. 3, pp. 302-322
Sharland, 1. J. and Leverton, J. W., "Propeller and Helicopter and Hovercraft Noise,"Chapter 9 in Noise and Fatigue in Aeronautics, edited by Richards and Mead, John
-Wiley and Sons, 1968.
Shashady, A., Presentation of Calculated Rotational Sound Pressure Due to a Propellerin Forward Motion. Report R-22673-2. United Aircraft Corporation Pesearch Depart-
ment, East Hartford, Connecticut. January 1954
Shashady, A., Kemp, N. H., A Study of the Effective Radius in Propeller Sound Calcu-lation and on Analytical Integration for Sound in the Far-Field. Report R-22673-3.United Aircraft Corporation Research Department, East Hartford, Connecticut. F"abru-ary 1954.
181
Shepard, W.S., and Wolfe, J. R., "A Study of Noise Produced by a Helicopter Rotor-Tip Vortex Interaction," Paper presented at the Joint Symposium on EnvironmentalErf,.cte on UTOL Designs, Arlington, Texas, November 1970.
Silverstein, A., Progress in Aircraft Gas Turbine Development, NASA-TM-X-52240,Washingtoi., D.C., 1966.
Simons, 1.A, "Some Aspects of Blade/Vortex Interaction Helicopter Rotors In ForwardFlight," J. of Sound and Vibration, Vol. 4, No. 3, pp. 268-281, 1966.
Simons, 1.A., et al., "The. Movement, Structure and Breakoown of Trailing Vorticesfrom a Rotor Blade," CAL USAAILABS Symposium Proceedings: Aerodynamic ProblemsAssociated with V/STOL Aircraft, Vol. 1, Propeller and Rotor Aerodynamics, Buffalo,NY, June 1966.
Skudrzyk, E. J., and Haddle, G. P., "Noise Production in Turbulent Boundary Layerby Smooth and Rough Surfaces," J. of the Acoustic Society of America, Vo. 32, No. 1,pp. 19-34, Jan 1960.
Smith, M. J. T., "The Problem of Turbine Noise in the C!vil Gas Turbine Aero Engine,"ICA3 Psa., 68-35, September 9, 1968.
Smith, M.J.T., and Bushell, K., "Turbine Noise, Its Significance in Civil AircraftNoise Problems," ASME Paper 69-WA/GT-12, Nov. 1969.
Smith, M. J. T., and House, M. E., "Internally Generated Nol-e from Gas Turbine Eng-ines: Measurement and Prediction," J. of Engineering for Power, pp. 177-190.,April 1967.
Snow, R., "Correlation of Broad Band Compressor Noise,", MSc Dissertation, InstituteFmnd Biration Research, University of Southampton, 1970.
Soderman, P. T., Leading-Edge Serrations Which Reduce the Noise of Low-Speed RotorsTN D-7371, NASA Washington, D.C., 1973.
Spencer, R. H., "The Effect of Noise Regulations on VTOL Aircraft of the Future,"Vertiflite, Vol. 14, No. 10, pp. 2-8, Oct. 1968.
Spencer, R. H., "Application of Vortex Visualization Test Techniques to Rotor NoiseResearch," Paper No. 470, presented at the 26th Annual Natienal Forum of fhe ArAeri-can Helicopter Society, Washington D.C., June 1970.
182
Spencer, R. If. and Sterafeld, H., Jr. Measurements of Rotor Noise Levels andEvaluation of Porous Blade Tips on CH-47A flelicoptcr, USAAVLAES TR 69-18,U. S. Army Aviation Material Laboratories, Fort Eustis, Va., 1969
Spencer, R. et. al., Tip Vortex Core Thickening for Aplication to Helicopter RotorNoise Reduction USAAVLABS TR 66-1 U. S. Army Aviation Material Laboratories,Fort Eustis, Va., 1966
Sperry, W. C., Aircraft Noise EvaluationL FAA-NO-68-34, FederalAviation Adminis-tration, Washington, 1). C. 1968
Sperry, W. C. ; "Effect of Aircraft Noise on Environmental Quality," Federal AviationAdministration, Washington D. C., 1970.
Sperry, W. "Aircraft Noise Exposure: Background, Methodology, and Comparisons,"Federal Aviation Administration. Washington D.C. 1971
Spivey, W.A. "New Insights in the Design of Swept Tip Rotor Blades," Presented atthis 26th Forum of The American Helicopter Society, -1970.
Stave, A. and King R. J., The Annoyance of V/STOL Noise - Phase I, Impulee NoiseSER-50679, Sikorsky Aircraft, Stratford, Conn., 1970.
Stepaiewski, W. Z. and Schmitz, F. H., "Possibilities and Problems of AchievingCommunity Noise Acceptance of VTOL", International Congregs of the AeronauticalSciences, ICAS Paper No. 72-34, September 1972.
Sternfeld, H. "New Techniques in Helicopter Noise Reduction," Noise Control, Vol. 7,p.-. 4-10, May 1961.
Sterufeld, H. Influence of the Tip Vortex on Helicopter Rotor Noise NASA N68-13150,Washington, D.C., 1968
Sternfeld H. Jr. and Hintorkeuser, E.; "Effects of Noise on Commercial V/STOLAircraft Design and Operation," J. of Aircraft, Vol. 7, No. 3 19,10.
Sternfeld, H. and Spencer, R. H., "Operatloual Aspects of Helicopter Noise",Paper 855A. SAE Air Transported Space Meeting, New York, April 27-30, 1964.
Sternfeld, H. and Spencer, R. H., Recent Research in Rotor Noise Reduction, SAEPublication No. 690684, October 1969.
Steruleld, H., Schairer, J., and Spencer, R., An Investigation of Helicopter Trans-mission Noise Reduction by Vibration Absorbers and DampinqTR 72-34, U. S. ArmyAir Mobile by Research and Development Laboratory, Fort Eustis, Va., 1972
183
Stcrneld, If., et. al., Acceptability of VTOL Noise Determined by Absolute SubjectiveTesting, CR-2043, NASA, Washington, D.C. 1972.
Steriifeld, if., et. al. , An Investigation of Noise Generation and Hovering Rotor, Part11, ilepart D210-10550-1, U.S. Army Research Office - Durham, 1972.
Sternfeld if., "Can Helicopters be Good Neighbors", Proceedings of Inter-Noise 73,pp 438-444, 1973.
Stevens, S. S. "The Measurement of Loudness," J. Acoustical Society of America Vol.27. No. 5, 1955.
Stevens, S. S. "Calculation of the Loudness of Complex Noise," J. Acoustical Societyof America, Vol. 28, No. 9, pp. 807-832, 1956.
Stevens, S. S., "Procedure for Calculating Loudness: Mark VI", J. of the AcousticalSociety of America, Vol. 31 No. 1 pp. 1577-1585, 1961
Stevens, S. S., "Perceived Level of Noise by Mark VII and Decibels (E)", J. of theAcoustical Society of America, Vol. 51, pp 575-601, 1972.
Stowell, E. Z., Deming, A. F., Vortex Noise from Rotating Clindrical Rods. -NACA519. National Advisory Committee for Aeronautics, Washington, D.C. 1935.
Strahle, W. C. "On Combustion Generated Noise, "J. of Fluid Mechanics, Vol. 49,part 2, pp. 399-414, 1971.
Strahle, W. C. "Some Results in Combustion Generated Noise," J. of Souud and Vibra-tion, Vo'. 23, No. 1, pp. 1.3-125, 1972.
Strahle, W. C., "A Review of Combustion Generated Noiae", Paper 73-1023, AmericanInstitute of Aeronautics and Astronautics, October 1973.
Strahle, W. C. and Shivasbankara, -B. N., "Experiments of Combustion Generated Noise,,"Presented at the Interagency Symposium, Stanford University, California, March 28-29,1973.
Stuckey, T. J. and J. 0. Goddard, "Investigation and Prediction of Helicopter RotorNoise. Part I. Wessex Whirl Tower Results, "J. j.ound and Vlbration, Vol. 5, No. 1,pp. 50-80. January 1967.
Surendraiah, ,M., An Eperimental Study of Rotor Blade - Vortex Interaction, Cr--1573,NASA, Washington, D. C., 1970
184
Swift, G. "A Study of the Sound Pressure Field Near a Propeller In Forward FlightWith Particular Reference to Phase Evaluation, " Masters' Thesis, The University ofSouthampton, 1965.
Tanner, C. S., Measurement and Analysis of Noise From Seventeen Aircraft in LevelFlight (Military, Business Jet, and General Aviation) , FAA-RD-71-98, Federal Avia-tion Administration, Washington, D.C., 1971.
Tanner, C. S. and Glass, R. E., Analysis of Operational Noise Measurements in Termsof Selected Human Response Noise Evaluation Measures, FAA-RD-71-112, FederalAviation Administration, Washington, D.C., 1971.
Tanner, H. K., and Morfey, C. L., "Sound Radiation from Broadband Forces in Circu-lar Motion," Loughborough University of Technology, Symposium on AerodynamicNoise, September 14-17, 1970.
Taylor, F. W., "Helicopter Blade Slap," M. S.C. Thesis of the University of Southampton,England, 1965.
Tedrick, R.N. and Hildenbrand, R. W., "Progress in the Development of OptionallyQuiet Turboprop Engines and Installations," Paper No. 730287 presented at the SAEBusiness Aircraft Meeting, April 3-6, 1973.
Tempest, W. , "Loudness and Annoyance Due to Low Frequency Sound," Acoustic,Vol. 29, pp. 205-209, 1973.
Theodorsen, T., General Theory of Aerodynamic Instability and the Mechanism ofFlutter, Rept. 436, National Advisory Committee for Aeronautics, Washington, D.C.,1935.
Tracor, Inc., Community Reaction to Airport Noise, CR-1761, NASA, Washington,D. c., 1971.
Tyler, E., "Vortex Formation Behind Obstacles of Various Sections," PhilosophicalMyazine.1 Vol. 11, No. 72, Apr. 1931.
Tyler, J. M., Sofrin, T. G., "Axial Flow Compressor Noise Studies," SAE AeronauticsMeeting, 345D, 1961.
Van de Vooren, A. I. c.nd Zandbergen, P.J., "Noise Field of a Rotating Propeller inForward Flight," J. of the American Institute of Aeronautics and Astronautics , Vol.1, No. 7, pp. 1518-1526, 1963.
Vogeley, A. W., Sound- Level Measurements of a Light-Atrplar.e Modified to ReduceNoise Reaching the Ground," Report 926, NACA, Washington, D.C., 1948.
185
Von Gierke, Hi. , Impact Charamctertzatiof of Noise inclutLdng mpLiajns of Ide.ti
n An hieving Levels of Cumulative Noise Exposure, Envirionmentai Protection Agency
Aircraft/Atort Noise Study Report, NrID 73.4, July 27, 1973.
Von Karman, T. and Sears, W. R. "Airtoil Theory for Nonuniform Motieno J. of the
Aeronautical Sciences, Vol. 5, ±io. 10, Aug. 1938.
Von Niekerk, C.G., "Ncise Generation in Axial Flow Fans," J. of Sound and Vibration'
Vol. 7, No. 2, pp. 31.0-311, 1968.
186
Walker, G. J. and Oliver, A. R. , "The Effect of Interaction between Wakes fromBlade Rowe in an Axial Flow Compressor on the Noise Generated by Blade Interaction",ASM.'E Paper 72-GT-15, March 1972.
Walsh, R. G., Jr., Leading-Edge Pressure Measurements of Airfoil Vortex Inter-action , ASRL-TR-153-1, Aeroelastic and Structures Research Laboratory, MIT,Cambridge, Mass., !970.
Ward, J. F., "Helicopter Rotor Periodic Differential Pressure and Structural ResponseMeasured in Transient and Steady-State Maneuvers", .Paper No. 423 presented at the26th Annual N.tional Forum of the American Helicopter Society, Washirigtk, . C.,June, 1970.
Watkins, C. E., Durling, B. J., A Method for Calcuhtion of Free-Sýpace Sound -
Pressures Near a Propeller in Flight Including Considerations of tha Chordwise BladeLoading. NACA TN 3809. National Advisory Committee for Aeronautics, Washington,D. C., November, 1956.
Watter, M., "Prog:ers Report on the Reduction of External Helicopter Noise WithProceedings of the ARPA Workshop," IDA Research Paper, Washington, D. C. I May24-25, 1968.
Wells, R. J., "Jury Ratings of Complex Aircraft Noise Spectra Versus CalculatedRatings", Paper presented at the 80th meetiags of the Accustical Society of America,November, 1D70.
Whatmore, A. R. " A Study of Transient Noise from Helicopter Rotor Blades", M. Sc.Thesis at the Unive~sity of Southampton, 1968.
White, R. ?. ,"VTOL Periodic Aerodynamic Loadings: The Problems, What is BeingDone and What Needs to be Done", J. of Sound and Vibration, Vol. 4, No. 3, pp. 305-344, 1966. -
Widnall, S. E., "A Correlation of Vortex Noise Data From Helicopter Main Potors,"Journal of Aircraft, Vol. 6, No. 3, pp. 279-281. May-June 1969.
WidnalU, S. E., "Helicopter Noise Due to Blade-Vortex Interaction," J. of the AcousticSociety of America, Vol. 50, No. 1, (Part 2), pp. 354-365, July 1971.
Wilkes, L. H., "Noise Research on Helicopter Rotors", Research Paper R. P. 349,Westiand Helicopters Limited, England, 1968.
Williams. C. E.. Pearsons, K. S., and Hecker, M. I1. L., "Speech Tntelligibility inthe Presence of Time-Varying Aircraft Noise". J. of the Acoustical Soclety of America,Vol. 50, No. 2, pp. 426-434, 1971.
187
Willi:inis, C. E., et. al., The Spteech interference Effects of Aircraft Noise, FAA-DS-67-19, Fedvral Aviation Administration, Washington, D. C. 1967.
Williams, J. M. and Berthoud, R., "Helicopter t ise in Central London", Social &Conmmunil.y Planning Research Paper P. 184, Noveinber 1970.
Willmarth, W. W., "S)aee-Time Correlations and Spectra in Turbulent BoundaryLayer.," Memo 3-17-69W, NASA, Washington, D. C., 1-22 (1952).
Wilson, L. N., "Experimental Investigation of the Noise Generated by the TurbulentFlow Around A Rotating Cylinder, "J. of the Acoustical Society of America, Vol. 32,No. 10, pp. 1203-1207, October 1960.
Wirt, L. S., "Gas Turbine Exhaust Noise and Its Attenuation, " SAE Paper No. 1002B,January 1965.
Woodley, D. It., "The Suppression of Power Plant Noise in Helicopters", D8-2139-1,Boeing-VerLol, Philadelphia, Pa., 1968.
Wright, S. E., "Sound Radiation From A Lifting Rotor Generated By Asymmetric DiskLoading," .1. of Sound and Vibration Vol. 9, No. 2, pp. 223-240,1969.
Wright, S. E., "Waveguides and Rotating Sources", J. of Sound and Vibration, Vol. 25,No. 1, pp. 163-178, 1972.
Wright, S. E., "Spectral Trends in Rotor Noise Generation." Paper No. 73-1033preseuted at the AIAA Aero-Acoustics Conference. October 1973.
Yeowart, N. S., Bryan, NM. E., and Tempest, W., "Low Frequency Noise Thresholds",•J. of Sound and Vibration Vol. 9, No. 3, pp. 447-4j3.
Yeowart, N. S., "The Evidence for a Reduction in Calculated Noisiness and LoudnessDue to Ambient Noise" D6-25358TN, Boeing Vertol Company, Philadelphia, Pa., 1970.
Yeowart, N. S. , "Acceptable Exposure Level for Aircraft Noise in ResldentialCommunities", J. of Sound and Vibration Vol. 25, No. 2, 1][72
Yudin, E. Y., On the Vortex Sound from Rotatin Rods. NACA Tech. Memo 1136.Natior.al Advisory Committee for Aeronautics, Washington, D.C.
Zandbergen, P. J., "On The Calcuhtion of the Propeller Noise Field Around Aircraft,"National Aero-and Astronautical Research Institute, NLR-TM 0. 23, p. 46, Amsterdam,Netherlands, June 1962.
188
Zepler, E. E. and Harel, J. P. , "The Loudness of Sonic Booms and Other ImpulsiveSounds", J. of Sound and Vibration V31. 2, No. 3, pp. 249-256, 1965.
Zwicker, E., Flottorp, G., and Stevens, S. S., "Critical Bandwidth in LoudnessSummation," J. of the Acoustical Society of Amet ica, Vol. 29, pp. 548-557, 1957.
I