8

REPORT No. 729—.

TEST OF A SINGLE-STAGE AXIAL-FLOW FAN

ByE. BAETON BELL

SUMNIARY

A ~“ngle-siage axial @ was built and tesied in the*hop of the pro~eller~eeearch tunnel of the NA(?A. The@n coxnpriaed a single %@.ade rotor hating a diameterof 91 &he8 and a sokiity of 0.86 and a wt of S7 eon-traoana hwing a eoltiitg of 1.98. The mior UMSdriwn@ a M-horsepower motor capable of rotating at a qeedof MOOrpm. T7Lefan was teded for ralume, preswre,and ejieieny ow a range of delirery pre.wuw andaohmes for a m-de range oj contrawne and blade-angleaeiting~.

l%e test resuh are presented in chartform in terms ofnondkmeional units in order that n“mila.rfarw may beaceuratel~ designed m-i%a minimum of .q40rt. The maxi-mu-meficien~ (88 percent) w obtained bg thefan at aMade angle of W“ and a contrawne angle of 70°. Ane~nq of 80 percent wag obtained by the fan with thecontrawrnes remmed.

INTRODUCTION

h connection with tests of airphbne cooling systemsthat are being ocmductwi in the propeller-research tmn-nei of the National Advisory Committee for Aeronau-tics, the need was felt for information on axial-fandesign inasmuch as the indications are that such fansW be usedin airplane ccoIing systems in the immediatefuture. In designs of aimraft with submerged engines,it may becomo necessary to provide a ti that willfurnish the neoessary voIume of air to cool the enginqthe oil coolers, and the intercooIers. In pu&er-propel-Ier radial-engine instaIIations, the uaq of ‘an axial fanmay help to scdve an otherwise diflicult ocol.ing prob-Iem. The deeision was therefore made to build anaxkd-flow fan with adjustable blades and contravenesand b conduct a series of performance tests on it.The reauIts of thsse tests me described herein, and thedata may be used as a basis for preliminary designstudies of superchargers of the &al-fan type.

These data are limited to the chraoteristics of oneparticular fan tWed over i range of blade and con-travene settings. No information is given on theeffect of such vmiabIes as adidity of blades and con-trava-nes, Mach number, staging for higher pressures,or use of vfmicme airfoil sections.

Since the tiuame of this report in preliminary form,errora of from 3 to 10 perhmt were discovered in the

pressure and efficiency curves. This error was due torotation of the air tilde the space downstream of thefan hub and affected the reading of the pressure y,. A ..,.slight alteration to the t%t sekup corrected this souroe .of error. The tests were then repeated and the cor-rected data me inserted in this report.

DESCRIPTION OF APPARATUS . .

The &ngle-stage axial-flow fan was built to be used , .primarily in cooIing and duct studies; consequently,an attimpt was made to obtain as high a combinationof pressure and volume as was consistent with the limi-tations imposed by the motor power and the fandiameter. Preliminary computations indicated that avolume of 9000 cubic feet per minute at a pressure of78 pounds per square foot could be obtained. Thisemdition corresponds to 21.2 horsepower. The valuesin terms of nondimensional qtantity and pressure

--.-—--

coefficients are Q/n.lF=O.446 and CZ=0.298 with thefau rotating at a speed of 3600 rpm.

The gener@ arrangement of the blower and the test ‘ --set-up are shown @ figures 1, 2, and 3.

.

The rctqr assembIy is shown in iigure 4. Attachedto the rotar hub are 24 blades that give a solidity of0.86, the solidity being defined as the result of bladechord times blade length times number of bladesdivided by disk area. The disk area is the area sweptby e bIades. Figure 5 is a sketch of an indiv&Iual

Pbla e. Each bIade is of R. A. F. 6 section and has ama&mm thickness of 12 percent of the chord. Each

~.. .

FImn L-~W 0[ arh-kul Wran&rrwlt km W@FIQCFend.

49

50 REPORT NO, 720--NATI0Nm umsoRY COM3fImEE FOR AERONAUTICS

FImrRE 2.-View of sxlel-taoui-sngementrmmexitend,

were made at various times during the Lusts. hyvariation in the no-load torqur, caused possibly Lychanges in lwaring friction, was aIIowtxl for in tbv datu.The torque coefficients include Lho torqur nccrssary torotate the hub as well as the blades.‘ The ehwtric motor, which supports tlw ftm hub nml

blades on its shaft, is mounted insido the fan casingby four strwmdine struts. Etwh strut, contuins fourorifices on each side, which www used for measuringthe quantity of air flowing. The prmsuro Uiffwmcebetween tke orifices and the atmosphere was cali-brated against quantity of air flow. A venturi tubewas used for this calibration..

The casing of the fan was of rcdlcd and wrkled steelplate, bored to a diameter of 21 inches nnd rclicvcd to

6.. /g”” Dkl -

I -/’

=% Ev?-k-ccu-?kwew.

dillPI(IUEI3.—Axhd4an test arruicemot.

blade has a straight twist of 2° p@rinch of blade lcngtband is not tapered. The blades were cut from didbar stock duralumin on a profiling machine and werepolished and btied by hand.

F~re 6 shows the ccmtravanes and the fixed’ hubawmmbly, Thirty-mvon contravenes with a sohdityof 1.33 wore used. l?iguro 7 is a sketch of an inchidualcontravene. The contravrme airfoil section was arrivedat by laying out an arbitrtuy camber line and usingan IVACA 0012 thicknees distribution. Tho ordinatesof the resulting section am given in figure 7. Thecontravenes were twisted 30 per inch of lengti andwere not tapered. The spacing between blade andcontravene center lines was 3 inches. A small clear-ance between the blade hub and the eontravane huballowed a sIight amount of cooling @ to flow throughthe motor.

Tlm power for the fan is supplied by a 25-horsepower,direct-current electric. motor. J3cfore it was mountedin the fan casing, the motor was calibrated with aProny brake for torque output as a function of arma-ture current at a constant value of fieId current. No-load runs with the fan rotor assembly (fig. 4) removed

a diameter of 21 ){6 inchm at thr fnn section. Th[Lcontravanca were rnountcd in a hub that was cmrhvlon the motur frame. The fan casing was carri[’dby a skwl framework on a welded tingle-iron brew,which was in turn mounted on rollwa resting on hard-ened and ground steel tracks. The rollms providod ameans of measuring the thrust produced by thu fun,The entrance cone for the fan was separahdy suppmtrd,as shown in the auxiliary view of figuw 3. Thmc was

FlmJmx 4,—AxhWnn bhdo whed.

TEST OF A SINGLE-STAGE AXCAIrFLOW FAN 51

Wew .44

$Eii55- ““”●

a close but free joint betwem the entrance cone andthe fan casing. A cylinder having a diameter. equal tothat of the hub and motor was projeeted upstream intothe free air far enough to extend beyond the pressurefieId of the entrance. The exit cones were independ-ently supported and were separated from the fan byan air gap. The working motion of the fan was there-fore free to roil fore md aft on its roIIeN to a limited

.

9

“

A

3;” 3*

‘ IL B

extent. Connected ~o the supporting framework andpadlel toend of the

the thrust axis was a thrust wire. Onethrust wire was oarried over a” pulIey and

4 7_l~”Dim.———

B

Wi?wxx

-—......w1

!!, rx

I“ 3“3*

ILyJ-

7“x

I1

t

A’ i4;= ---

,10=

&r+–/’-lSkCficrla’

FIGUBE &—AxM-fan blade.

-

..-.

.

station

4Ordinat%

o.Cs5.142.Is95.aMo.2-IO.23s6

:%.1775.U45.W

o.024.019

0

:E.!m.400.600

1:l%1.all

‘ SectionW -

FIGCM 7.—.AxIafEJIJI mntre.vane.

OontraveaesmMon

.

.

. ...

-#p& Loweradhak

o.025.m. lcdl.160-m

:E-ml.m

d%L!2CBI1.403L6ML~

k%

o.Oia.Im. WI.178.m

:E.m.s25.6W

:%4.242.176.0R6.050

0

0-.017–. Olti–. 015–:%

:&

:%.loi.ln.107.091.Oea.mz. Ou

o

L. E. radiusT. E.Ayflus

B

(LOW.0025wW

lfIWCU 6.—Axl8l-fm c01tfuvs2M wflK!L

52 mwom NO. 729-NAmONAL DVISORY cowmmm FOR AERONAUTICS

connected to a dial-balance head. The other end ofthe thrust wire was carried over a pulley and connectedto a weight pan. The dial balance and all oount.er-weights used were cerefully calibrated before the testswere made.

The exit cone was provided with a celhdoid \tidowthrough which tufts+ located in the air stream, could beviewed for the purpose of estimating the stream twistangle. At the dowmtream end of the sehup a conicalphg mounted on a screw thread was used for varyingthe restriction and controlling the volume of flow.

On the end of the motor, opposite the fan hub, wasmounted the generator of a ‘i?eeton tachometer. Thisinstrument was wired to a ndliamm eter, the reading ofwhich was frequently caIibratti against mater speed.

DESCMPTION OF TESTS

MI tests were run at a speed of 3600 rpm except. bcases in which the torque would have exceeded 36.5foohpounds, which corresponded to the motor rating.Under those conditions the tests were run at maximummotor torque.

A Serie9 of tests was run with sev-e@ cOntravane-angIe settings ranging from 40° to 70° and anotherseries was zun without contravenes, At each of theseconditions the bIade angles were varied from 5° or10° to 35° or 40°. The quantity and the pressurecoefEcients were varied by changing the restriction attie outlet of the test set-up. At each point, data werotaken of balance reading, amount gf counterweight,manometer readings of the static pr~e pc and of thepressure at the orMces in the motor support, bmometerreading, temperature, bygrometer reading, tachomet.wreading, motor field current, and motor armature cnr-rent. The angle @ flow downstream of the fan wasestimated by Iooking at the tufts.

Extreme care was taken in setting the blade and thecontravene angks but, because of the difllculty insetting them, they may not have been sat closer than+%’. BIade and ccmtravane angles were measuredat a radius of 7% inch= (71.4 percent l?). Both bladeand contravene angles were measured with respect tothe same reference plane, that is, the plane of rotationof the blades.

PRESENTATION AND DISCUSS1ON OF RESULTS

The ramh% of the test reported in this paper arepresented in a manner similar to that used for pro-pellers. IVondimensionaI coei3icients, which are applic-able ta any similar axial fan operating at or near thesame ReynoIds and Mach numbers, are used.

2’CT== torque coefficient

These coefllcients are p~otted against the quantitycoefficient Q/nDwhere:

17 fan diam8ter, 1.75 feetn rotational speed, revolutions per secondAp pressure rise across fan, pounds per square footQ quantity rate of flow, cubic feet per second -P mass density of air, slugs per cubic foot2’ torque, foot+ounds

ak!.o:

p. static preasore on downstream side of fan hubp blade tmgIe, degrees@ ccntravane angle, d&rees# stream twist angIe, degreesR bhule radius

The coefEcient Q/nP corresponds to Vjn.D as used forpropellers and is also proportional to the dischargeco~cient p as used in reference 1. For the. particularfan tested Q/n17=0.412 V/nD (where V=averagevelocity though the disk) and Q/~&—l.29P.

The presure rise across the fan was taken as tiethrust on the disk area &tided by the disk area. Thethrust on the disk area is equal to the thrust obtainedon the thrust system (balance and counterweights)corrected for the force resulting from pressure on thedownstream side of the hub, that is, p, measured ii thespace inside the tit cone. Thip correction wris eitheradded to or subtracted from the thrust, depenchig onwhether PC was below or above” atmospheric pressure.As the horizontal areas at the free joints on eith”m endof the blower outer cassg wqe small; the correctionfor any pressure dHerence at these point9 was neglected.No correction w-as made for apy pressure drop due toflow if cQoling air..

The coef6cient C?z is proportional to tbe preksurecaeficient used in reference 11which in the notation of”

this paper is Apj{u9, where u is the rotational tip speed. “

For this fan, 0, Z4.93 Ap/~ u’.

The results are pres~nted in &ures 8 to 28 as fo~ows:.

-= cmtzmfy&y*tk -

Sto il.-- .--. _----:----------------------- 40.12 to lo------------------------------------ ML16 to lo------------------------------------- 60.m to n-------__ --__ ------- .----__ -----IF--- 7Q. --24 to ~-----._--------_--_-__-_- No Cc@avanee.

28--: — ------------------------- Variation of fan c@-acteri&ios wfth m-rotational spe@...

Two plots of the pressure-coefficient data are presented.In one pIot, the test points are given and Iines of con-stant angle of twist downstream from the fan aresuperimposed. Ih the other pIot, lines of constantefficiency are superimposed to facilitate design work.

. .

*

.

.-.

.. .- —.-

.-

—.-

.- .=J.

!.-

TEST OF -A SINGLE-STAGE

.2q

I I I I t I

24 :------- 6bd3s Sfakd— ,, (msrb!bd

m .

.}6 . v

Crv“

/.12 . .“

,$=d

,.’ %

.m ;s m

-.---- u

d#

-a---- - Jo”,CM; w-

;’ >-p==~

0 J 2 .3 .4 .5qo

!i’tGuEE .s.-Tmque cmxllc!enb. +, &. “=

2.8.

!!1b

g- ------Rides Sfirrled2.4 : — # mfalled h

+ —-— Constmf stream mgle

FIGUEE9.—Pre9?um amefetms. +, 40=.

A!IKIAL-FLQW Fm 53

28 :

I

24 : --------- &&s srfdled— /, mtdkxf

/ 60

/.6 :1 -fy~‘. “. 50

c,/ ~ /

/

\l

\/ //

a“.

\

.8 : Y\ ‘ t - “ \

\ r)=30pemSnt

‘.4 : \

10*

r. . . .;-9 [,.,. ),, ,,

o J .3 .4 .52W

kmz 10.—Pmsure wemefents showingUnesof mnstantemckneg. +, W.

mum Ib-kdfmn emdenck.s. ●, W.

.

4

54 REPORT NO. 729-NA’!’IONMJ ADVISORY CO?d?41’rI’EE FOR AERONAUTICS

I3

.72.:40°

.68 :.--::------- stoh&dstoh&d i

,,

.64 :

.60 ;

/ o

/

.56 ;}

r

. } -—

.52 ;0 -... .— -,-

/ ( *

.48 :

#-,, { 300 “–

.44 :, }

$ 7-,

.’,’

) ‘00

.40:< .-

,’c,

,’/ j 3

.-, ----...<P’

.36 .. ,’

, P/’ .

. — —e

.‘ ,’.32 .

.’ ,0----.--4-, ,‘,’ .’ /

,.

.28 . 0 Fc r“. ..’,4‘. 4.0-- ,8’ ,’

#yw ~

25°1.24 .

t, k ,f’ ,d.0

d,d-

.2 0..

9’

.-.a.-....,J

./6. d,

0. P . . ...

id %2u“-a.a, ●

.12. ~----->

)4

-af/

.08L ,--- -4 --’m

/50

I:/?-5 0Au J..,,

0 ./ .2 .3 .4 .5 .6u. , —

.7 -8 .9 Lo L/Q/nD’

.—

TEST OF A $YIW3LE=TAGE A2ZMJ-FLOW FM

55

3.2

P

I2.4

2.0 :

Cp

}.2 -

G -

-—-(h+onf stream ongle

.4 .

.8 .9.3. . .4 s ~ .6 .7

0 ./ .2 QJnD

FImms la.-~ Coefficlmb. +, w.

. .

56 REPORT NO. 72f+NAT10NAL nvmoxiy COMMmEE FOR AerOnaUtiCS

3.2

F

2,8 — \

~

..

2.4

\

.-

2.0/ 7;5k

\

c=/

/

\ , /

/.

‘“

, -----

1.6- ~~ /

f/

1,%

25”

f. 2 \

s h= . ~’

,.?7=50 pa-cent

.8\

—

\\

I I

-.-— —..—

.4 -----●

!5”-.— .-...-. .—r. — .—.

fl=5”/0°

1 , I t ,0 ./ .2; .3 .4 .5 ‘“ ;6 .7

Q/nDsFmwm lL—PreeswecoeellelenteshowingUmad ooummt etlldency. 6 E@.

.

. ... .- ._ -,- .- _.,

..— ,

—..—.—.- . . . . . .-. .

-. .-., . .

. . . .. ...=.

—.. — -. .— ——--

—. . .

.. . ..—

.8 .9

80.— —..— .. ..— —,---- .–— ------

— —.

60

\0

* /.’

0 */“

/.— .-—

unstalled -

0 .( .2 .3 .4 .5 .6 .7 .8 ,9Q/nDJ

Ftww15.-h1d4aJI emdencki +, w.

. mt,f;.{,d, ,/

20

.

.

*

TEST (31’ A S?XGLE-ST.4GE AXIAL-=OW F~ 57 -

....

.,“.

.

F[GUM I&—Tarqtre cc.a%cfents. ~, ~

58 REPORT NO. 729—NATIONAL ADVISORY COMM-E FOR AERONAUTICS

4.0 — .-—--..... — —-.-.— —0

------Blades stalled. . . .--, ..-, . -

0

3.6 —.. .,- ..—

.3.2

2.6

r

(.6 , ! , 1.

\

T //fl

/

/ / ,,

/ //

,.-)

f

11,. /

/

f1.2 /

lb .’1

/

, /’ I / \ -

–~–-4 ----4 -—-4 ----1

w-}-l-i,“

~ -10”

2.4

w 4’1/’ “ ~~ ~ ‘“ %

/’ / ... . . . ..._.

t), ,/ .

t

7-— . .. . . .— . .

‘.Q%

\\ b -,/ ,’

/’ ,_J~U

-- .

,/

1 . .-. —

~

‘w-q ? “:”~ +’;’ v ./ 1’ / (1 “-/

/

/

/

L

30”.-

.—. —.

i M / A

/

!

/

/-.—. .__. . . .- -

.,.

b .’/ !3 ; / -125”

,.

0 .! .2 -3 .4 .5 .6 .7Q/rzDJ

.8 .9

FKWBE 17.-Prwwre omllchts. ~, IKP.

TEST OF A SINGLE-STAGE AXIAL-FLOW F&N 59

.32 :

/

2.8 \

\/

/

2.4 ) \ /’ / \

./

\/ \

/ /

/

I I IAY-KIY I I %kw ‘35”

/ ‘v

II K,. t/

\1.1 H ;’=; I \ ...

L2.0

F \,\ ~\, ~hJ t h I I/l I\#t’ I I I Ju-1 t

, A —- 1

II I d\ I N \ I 1 I \ t I A I \ I

.

I

.8L L

‘f lN\N--+-t-177/i’\lP’NJ I TN-H+-T7” I lJil- .

\l w! ! \,&+q-.60L3-

,——IL------q=;Opc+emf

I

.4 \ 20”

\,

)= foe r6=

, , I , t * , 1 t , to .1 .2 .3 .4 .5 .6 -7 .8 .9

Q~d3

FIGURE lS.—Prassure coefflcknfuhwhg lhm of constant *U. +, ~.

60

60

Q

e I f t

A4 .

o“ ./ .2 ..3 .4 .5 .6 .7 .8 .9@.@3

R(PJM 19.—Axfalfmletrwfolmfes+, m.

—.

.-

00 REPORT NO. 72*NATIONAL ADVISORY COti17TEE FOR AERONAUTICS

.m~

. .— ~

6’? :x

x~.... . .— ___ . ,- ~., , ....

------------ Blqdes Sfof/ed , /’ 45”t, unsiu!led

. . ---- ...- ._. .—

.60 :

s.

, .-— —-- --=. .-—

.56 -

x

s 8

x

.62

.

/x

71

...-.

.+% //

—. . ..— -.

.44 - — — — — — — — — — — — — / — # c

-

—

>

— 2s L. --- --- -...40°

iJ%r

d

.40 ., d

Y,...,

;’Po

.36 :,

.- — .—, —

cT- ; ...-—. ..-.,,

.32 . .’ 3,’ ●,“ Y!

.’ ,’

.28. ;.#‘ .’

.x ,“ 9’ H.’ , 3

.’ d AI t 1 l=”l I [-”-rl—~ “~t, J,.’

.24.,6 to+, # ,

,‘ . (#

—.#--- 0 -=% ~

b ““II—-—1

I

-0. . .

.20 :~. .x- #- ,0

. . . d/ .—

‘a.D’ .

. . .“* , . >..- ,‘. ..0 k

- . . .——,

/3, . . . . ..- ,~

. t6 . . 309,’ ‘~ P“ ~

,’ . %b ‘u ,*. A+

./2 . 0’a-. 9’

‘-w, ‘&

---- # ~ h‘i 25°

r

I. , , , , ?

I I 1

.-

.

k..i..l..lil..i....i..li.il.ii.i..ir.i...i.i...i....i...i....i....i...i....i....i....i..U-.

0 J .2 .3 .4 .5 .6 .7 .8 .9 /.0 /.1 L?Qp’lD’

FIGURE !M.-To!’qus ~mcienh +, 7CP.

TEST OF A SINGLE-STAGE AXIAL-FLOW FAN 61

l...ilrti.llli!i.!.illl!..i...[...l..li...ir1.i...irllli....i1lpi...1i..i.i..i..i.J“

p=fo” 15”

0 J .2 .3 .4 .5 .6 .7 -8 .9 LO Li 1.2Q~nD’

~QUM 22-kR3SUXt ~ts ShOW@ _ Of =-t a-. +, ~.

62 REPORT NO. 729-NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

I(X71 -— .- — --

80 : . T

f ,’260 “

i! ~* P

J

t

.- .. .- — .. .—

;40 : . .

a------------Nudes stoned

a mstulkd ““~‘/5” .—.

u ./ .2 .3 .4 .5 .6 .7 .8 .9 LO 1./ UQ/nil’

FIGURE23–Axia14m e5cImciw. &W.

.24 I I I-------- !-- B/odes sfatkd

I—. . .. . undd..ed

.20

L.%d -w

./6

Cr :% 1

./2t

P r ‘%35*

Ho4

30°0

.08 ; * s-a :, *“ -y-u” -

..~,-o~ - }

25°

.04 -f -- –~ -* --m - B=iu* %5”

20°

0 .f .2 .3 .4 .5 .6QjnD3

o .1 .2 .3 .4 .5 .6@Da

.

FIOUBE 24.—T@rque coefllclmts. No crmkavanw. FIGURE2s-Fhrsura cwEicknts. No cmirmma

TEST OF A SINGLE-STAGE AXIAbFLOW FAN M

r

2.0

1.6

i.2

%

.8

.4

0 ./ .2 .3 “ .4 .5 .6Q/d’

FrGU~E23.-Prea?umcoef%ckotsshowingMm of mnstsnt e13iciency.k-o Caqavam.

The stream angIe #, for which constant vahm areimposed on the pressure-coefficient plots in @urea 9,13, 17, 21, and 25, is the average stream angl~ as estim-ated by viewing the tufts located behind the bIadewheel. Under certain conditions there was consider-able variation of the angIe along the radius. lt isbelieved, however, that tbe stream angle of most ofthe air was within +3° of that given. Positive vahsof # indicate that the air steram was twisting in thedirection of rotation of ‘the rotor.

The maximum efficiency of 88 percent for this funwas found to be at a blade-angle setting of 30° and acontravene setting of 70°. It is interding to note. thatthe contravene setting of 70° yieIded the highest ef&ciencies for nearly alI vahms of Qjn~ a.

The fan eficiency with ccmtravanes removed was 80percent as compared with 88 percent with the contra-venes set 70°. Tl& loss of 8 percent resuhs from the

/m

80

&o

. *.k5-

20 I,8.1P

0 J 2. “3 .4 .5 .8

FMWEE21.-Ax&?l4m eSklenc!rs. No mntramws.

fact that the rotational losses occurring without con-travenes were greater than the profile drag of the ccin-travanes. The downstream angle of twist for the peak-

.-. .—

dliciency condition with contravenes set 70° was about -5° or 100, whereas the angle of twist with contravenes .__:removed was about 25°.

Of perhaps more importance than the effect on efi- .-.ciency is the effect of contrawmes on the pressuresproduced. The maximum pressures for a given quan-tity of flow were found to be considerably kss withcontravenes removed thun with them installed, regard-less of the blade-angle setting. RIen the contravenes .........

RofOfionOlspeed, n,rps

.-

FkicFtE ‘a.-Variation of fanchmaderisticswithmtatkmdsrml. QldP,0.+%A Z&;+.. w.

w~e remov~, the rottttion~l interference velocity wasin the same direction as the blade rotational veIocity. .-

The result was a certain relative velocity over theblade surfaces and, consequently, a certuin pressure.When the contravenes were m place, the air was givenan inflow rotational-velocity component opposite indirection to that of the ~tor, the result being anincrease in the reltttive velocity between the air and therotor blades and an increase in pressure.

The stalling cha_mcteristics of the fan were wry pro-nounced. b Iong as the blades were unstalled, opera-tion was very smooth. & the rdriction was increasedand the flow was decreased, however, the fan reached astalling point beyond which the operation became very

=.

64 REPORT NO. 72-NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS ;

rough and” nOiSy. In some cases the quantity of airflow dropped 04 considerably with stalling, and it wasimpossible to obtain points for a curve, On all thecurves, the stalled portion is indicated by clotted lineswhen enough points could be obtained to justify it.It is recommended, however, that fans be designed tooperate only in the unstalkd portion.

As the range of this fan was limited by both thetorque and the speed characteristics of the motor, littleatt~mpt was m~de tQ get an extensive evaluation of Iscale &eCt. One series-of tests was made, however, atI!3=25° and +=70° for a short range of Q/n~ at differentblower speeds. Values of C=, C,, and T were takenfrom these tests at a value Gf Q/@= 0,45. Thgsevalues are p]otted in @gure 28 agai~t fan rotation@speed, and the results indicate tht, while the pressureand the torque increase, the efficiency decreases withReynolds number, The variation of pressure and

torque coefficients with Reynolds numbw is unmpcchedly lmge.

No eflwts from compressibility would ho exprctwlfmm these tests, inasmuah as the highest tip speed wasonly 330 feet per second. Compressibility should betaken into account for designs wherein the tip speedswill be above 600 feet per secoml.

LANQ~EY MEMORIAL AERONAUTICAL LABORATORYI

“NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS,LANGLEY FIELD, VA., S@ember 2%, 19.#1.

REFERENCE

1. Keller, Curt, Marks, Lionel S., and Weskc, John Il.: ThoTheory and Performance of Axhl-l?lowFans. McGr&w-Hill Book Co., Inc., 1937.

?

1SlI1~ f(F;>J 69 (13PI:l 47)Bell, E. Barton

AUTHORrslAMER. TITLE, Tes t

fORG'N. TITLE,

DIVISION, Power Plants, Reciprocating (6)SECTION, Cooling (1)CROSS REfERENCES, Fans, Cooling (~106); Fans, Axial

1"1"" - Design (34704.15); Fans, Axial n"" - Perfonn­ance (~704.3)· *

of a Single-stage axial-flow fan

ORIG.AGENCY NUMlIEB

R 729REVISION

\' .for Aeronautics, Washington, D•....Q..,

fEATURESpho tea, diagrs, graphs

.T-2, HQ., AIR MATERIEL COMMAND

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@ ,17/3/1

~I-)')"l~b' Acrw Far?6 .

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