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https://ntrs.nasa.gov/search.jsp?R=19760020430 2020-06-02T15:01:35+00:00Z

NASA TECHNICALMEMORANDUM

(NASA-f!1-X-7 ? U CC) FL(W VISUALIZATICb

LCNG y ECK E11PHCLTZ BFSCNATCRS WITH G1

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FLOW VISUALIZATION IN LONG NECK HELMHOLTZ

RESONATORS WITH GRAZING FLOW

by Kenneth J. Baumeister and Edward J. RiceLewis Research CenterCleveland, Ohio 44135

TECHNICAL PAPER to be presented atthe Third Aero-Aco, ,s Conferencesponsored by the American Institute of Aeronauticsand AstronauticsPalo Alto, California, July 20-23. 1976

IN.

JUL

RECEIVEDf, NASA STI FACII ilta INPUT 8RA.NL

dIUW VIOUALIZAY;',:: III LON(; NECKHIiLI•iFOLTL LESDIMORS WITH GRAZING IlVd

Kenneth •', baumciater and Edward J. RiceStational Aeronautics and pace Administration

Lewis Rq noarch CenterCleveland, Ohio 441',%

Ahntract

1'oth oncillutia iS and steady flown were appliedto a cinrlu Ple;:i glow- resonator cavity with ^•ol-ored dyes in,iectcd in both the orifice and Cra.•cinCflaw fieli to r000rl the motion of the fluid. For)ncllLitory flow, the in:=tantaneous dye :.tremallneewere similar for both the short and lon:•-hock or-ifice., he orifico floe blovkarc appoarc to to in-donendent of on Tice 1en,,th for a fixed amplitu]eof ]low oscillation ant ma gnitude of the rrazineplow, '!lie ate:.:dy flow -ye rtualea showed that these7uatle and steady i'i.ow resistencec du not necec-nurily correoponr Tor lonl7, neck orifices.

Introduction

Either oscillating or steady flow can be ap-plied to the resonator through the valvim , chown inFitt. 1. The oscillatory flow was intended to aim-ulate acoustic oscillations while the steady flowwan intended to simulnte a common method of mean-uring, the resistive portion of the resonator im-pedance. The flow oscillations to the resonatorcavity arc driven by a nervo-controlled hydraulic-ally operated Vinton, as shown in dig. 1, i'he Sds-ton could to oscillated from U.1 to 50 hortz. Forthe purpose of these experiments, the frequency wascat at 2 hertz. At higher frequoncion (;;renterthan 10 Iiz), the equipment had a tendency to vi-brate. At frequencies lower than 2^. hertz, the re-oultim, pulse was not sinusoidal. This lattur ef-fect war thought to occur because of recunaree inthe fluid line.%

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.cepite 4oncideraUa research dur : the lastaoca,e, there in ::till mvch unknown uot-erning thedechanlem of acoustic crer;y dionipation by a roco-orrtor in the preccnco of eraainc flow. More de-tailea information in needed re,,ard'lnC the physicalflaw interaction proce.0 oocurrin,; near the mouth ofa 1 :elx bolt:: resonator in the pronence of ,crazingflea. 'lu uncertain the nature of the flow processfor hint •. neck resonators, a vioual study of the of-fact of ,%razin,, flow on the oscillatory flow in alon, < neck orifice has been performed in a plexiglasoflow channel with a ninCle side branch Heliftholtzreconator using water an the fluid media and cO.-cred dyes to trace the fluid motion..

In this investigation, both oscillatory andsteady flow were applied to the back cavity of thelong neck resonator. The motion of the dyes andthus the fluid are recorded by a hiCf- speed aware,Individual motion-picture frames are presented inthin report to illustrate the flow regimes, Themotion picture

from which the still photoLmapho in

thin re port were taken may be obtained by contactingthe authors,.

f,rraratus and Procedure

Figure 1 is a schematic diagram of the tent up-paratus, ; he apparatus is essentially a once-throu <h water flow system, fhe main channel is9O cm long with a reetanirular crocc section 2,54 emby S cm, F.etaila of the short neck resonator cav-ity are shown in ar, 2, while details of the lourneck resonator cavity are shown in 1.11. Forboth so-so, the orifice hole is a square 1.27 by1.27 em. The square ;;eometry rather than a circularone was chosen for cane in photographing the flow.The short neck resonator has a lergth to diameter(hydraulic) ratio of 0,5 while the LJD of the longneck resonator is 4.

'Three different color dyes can be injected in-to the flow field (see Pig. 1). The dye flows un-der the action of Gravity to the dye injection lo-cations marked in :'1gs, 2 and P. 'fhe needle valvesshown in Fir„ 1 were adjusted to prevent ,jettin¢ ofthe dye co as to minimize any disturbance to theflow field. Water soluble dyes were used.

For convenience, the oscillatory+ flow vac ap-plied to the reconator cavity rather than the main:stream• In this munner, the magnitude of the flowoscillation in the orifice could be precisely cun-trolled by varying the stroke or the piston, itwan fvand experimentally In ref, 1, that the sametype of flow profiles in the orifice occurredwhether the flow oscillation was introduced in theback cavity or in the main stream. Uoin g thir: pro-cedure allows the resonator cavity to be full ofwater with no need for an air bubble to providecompliance,

The Crazing flow was measured with a turblr,eflovrmoter and the frequency of the piston was clopmeasured, The high-speed motion-picture corera wanpositioned adjacent to the resonator cavity. 'f hevelocity field in the orifice and in the main waterchannel can be determined from the high-speed no-tion pictures by following the movement of the dye,.

In the entrance region of the main flow chan-nel, a system of screens and baffle;: was added toproduce an initially uniform velocity profile in theflow channel. From velocity profile meacurementoreported in ref. l,. the "boundary layer" extendsapproximately 0.3 cm from the wall. This t',Ivan aratio of boundary thickness to orifice diameter(hydraulic) of around 0.25, which iz -mall comparedto the corresponding ratio in actual flow ducts.Although this may change the magnitude of the renic-tance, it should not chance the general character-ictfes of the flow regimes.

Durint a run, the Crazing flow velocity in themain channel wau first cot. Ilext, the frequency(2 Hz) and amplitudes of the resonator Slow per-turbation were set. Y} pally, the valves to the dyereservoirs were opened. Srhen desired, a high-speedmotion-picture -amera recorded the flow patterns,Generally, the camera was run at .00 framed persecond.

Scaling Considerations

The intent of thin ::turfy was to provide a vis-ualization and hence a better underntandin of theair flow process in a resonator orifice in the

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presence of a grazing steady flow. It is importantto consider whother the water system simulates anair system.

Aased on the wek of Thurston and Har rovc(Z)and Ingard and Iaing^l) , Hersh and Rogers ( I ) pro-vide convincing evidence that air-water bimilitudeexists for the resistance and reactance Tor flow inthe orifice. Reference 1 also discusses this topican well as presenting come numerical examples,

outside the hole, similarity of the air-watercyotem with Crazing flow may be inferred becausegrazing flow Reynolds numbera bated on the diarn-etern of the orifices are similar. Finally, theor+.rice to ; =ing stream momentum ratios are aim-ilar thus implying dynamic force similarity.

Orifice Flow Visualization

The following several flruren summarize theoscillatory flow and steady flow regimes for a.simulated resonator. orifice. The figures containsingle frames taken from a motion picture study.All the photographic cequencen are for Slow in theorifice in the presence of a grazing flood. Photo-rrapho of oscillating orifice flow in the aboenceof grazing flwa can be round in ref. 1.

Photographs for oacillatory flow for a shortand then a long neck orifice will be presented andcompared. Noxt, photoCrapho for oteady flow, intoboth the short and long neck orifice will be pre-ce.ted and related to the oscillatory flow. Thesteady flow in of interest since measurements on asteady floor system ue a practical way of eatimat-inC the orifice - stance to an oscillatingflow(5),

oscillatory ilod ReRirnec

The oscillatory flow regimen are illustratedin Fire. 4 and 5 which shows one cycle with bothinflow and outflow to a short and Song neck orifice.As documented in refs. 1 and 4, the resistance dueto Crazim; flow may be viewed qualitatively as anorifice blockage effect which is evident in thesequences in Fire, 4 and S.

In contract, in the long neck orifice ( Fig. b)the entering fluid at the top of the orifice isdirected downward by the action of a small eddyformed at the lower lip of the orifice. Partialdissipation occurs during the turning process, how-ever, sane of the kinetic energy will be directedback into the main stream of the crazing flow dur-ing the outflow cycle, Recall, in the short neckorifice all the kinetic energy was dissipated in theback cavity. Therefore, the acoustic rocictuncemay be a function of the length to dlernater ratioof the orifice.

On the outflow portion of the eyele t the or-ifiw flow is seen to encounter the large axialmomentum of the Crazing flow which must be dis-placed before the orifice flow can emorge. In boththe chart and long neck resonator, the outflowstreamlines look similar. The streamlines leaving,the orifice turn downstream in parallel with thegrazing flow.

One striking difference between the osofllat-ing flow in the short and long neck orifice in thepresence of an oscillating slug in the neck of thelone orifice. In the motion-picture study of thisoscillating slug, a red dye was used to mark theposition of the slue an a function of time. Tomake this slug visible in a black and white photo-graph,. a large concentration of the red dye wan ad-ded in the rear of the orifice, an shown in Fir.The inertia of the slug accounts for the increase inreactance that theory predicts for the long neckorifice.

Steady Flow Regimes

Zorumoki and Parrott ( 5) found for short neckorifices that the instantaneous resistance is in-dependent of frequency and in, therefore, equiv-alent to the flow resistance of the orifice. Theflow resistance is defined as the ratio of thesteady pressure drop across a material to the gt@adyvelocity through the material. Feder and Lean Calso chow a close correspondence between the aeouc-tic and steady flow resistances in the presence ofa [gazing fled.

Short NeckFor the short neck orifice an shown in Fig. 4,

during the inflow portion of the cycle ( t =. 0 to0.21 sec) the axial momentum (vertical) of thegrazing flow makes it difficult for the fluid tonegotiate the turn into the orifice. This resultsin a large separation or dead flow region at thelower side of the orifice which effectively reducesthe area of inflow. The inflow region in seen tobe limited to the small channel at the top of theorifice. For a long neck orifice, similar resultsare shown in Fig. 5 during the inflow portion of thecycle (t - 0 to 0.228 sec).

In the short neck orifice, the kinetic rnergyof the entering jet of fluid is diss ipated in theback cavity. At the beginning of flow reversal InFig, 4 ( t = o.23r sec), new flow from the resonatorcavity is pushed outward through the lower or dead-water portion of the orifice area while the inertiaof the fluid which had just entered the orificenear the upper surface continues to carry that fluidback int.; :he resonator cavity, Therefore, forshort neck o,it 'ices, the resonator cavity acts asthe sour^e of fluid for the outflow portion of theflow osci", . 4.-n cycle.

Ucing Fig. 4 as a basin for modeling the flowfields of a short neck resonator, Fig. C presentsschematics of the three flow regimes associated withone oscillation cycle. The flow fields of thesteady inflow and outflow from the resonator -latelyapproximate the instantaneous flow fields of theresonator due to an oscillatory flopr field, as seenin I'ie. 4, Figure 7(a) shown a photograph of theflow field for a typical. inflow setting, In Fitj-7(a) the back cavity was filled with dye and theInflow is shown by the clear region near the top ofthe orifice. The streamline represented by theouter edge of the dye closely approximates the dyestreamlines seen in Fig. 4 at t = 0 . 122 and 0.178seconds. Therefore, the steady flow visualizationconfirms the earlier obnervationo made by Zorumckiand Parrott ( 5 ) for inflow to the orifice. Similarresults occur for outflow.

Unfortunately, the treamlinon associated withoscillatory flow near transition from inflow tooutflow can riot be duplicated with a steady flowexperiment. The advantage of oscillating flo pr vis-ualization over that of steady flow can be seen by

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the cequeney t o 0,170 to 0.31? ascends in Fig, 4,At t s 0,170 coeondo, hint velocity inflow entersat the top of the orifice while a dead region so-aura at the bottom. As tine progroccoo, tho pros-aura drop acroas the orifice changes to a higherpressure on the left of the orifice than on theri&h (favors outflow), The hirh velocity jet re-giono cannot be iratodiately stopped and reversed.The dead rogior can, however, be more quickly ac-celerated to furm an outflow. Thus there is an In-start in the cycle where inflow exists on the topof the orifice and outflow exists on the bottomsuch that the not flow through the orifice is sere.Around this zero flow condition, a resistance-tire(or net flow) history should be produced which iscontinuous. In effect, the two-dimensional qualityof the dynamic flows will remove the discontinuityof resistance at zero through f }}ow which was ob-served by Budoff and Zorumski( 7 / and Rogers andHersh g)

Lon- deck

The atealy streamlines in a long neck orificedo not match, in general, the instantaneous dyetrace patterns in the two orifice under the con-ditions of an oscillatory flow, az Been by comparingthe dye traces in Figs. 7(b), (v ), and (d) to thedye lines in Fir. 5. I'or relatively low inflow, aszh mo in IIC. 7(b), the flow reattaches to the low-er orifice wall. Consequently, the cteady flow re-oistance measurement cannot be assumed equal to theinotaneouc oscillatory flow resistance.

For the larger inflow rates (Pig, 7(e) and (d),separation secure in the long; neck and the resonatorback proccure in felt at the vectream enhance atthe orifice, Under these conditions, the cteadyflow resistance ndght approximate the instantaneousinflow resistance.

Summary of Results

By means of colored dye traces, photographicsequences illustrate the detailed structure of anoscillating orifice flow with and without the pres-ence of a grazing flow field, Specifically, thefollowing maJor results were found:

1. For flow into the resonator with grazingflow, the orifice flora area blooko.Ce appears to beindependent of orifice length for a fixed amplitudeof flow oscillation and magnitude of the Crazingflow, For short neck resonators, all the enteringkinetic enerrar is dissipated in the resonator cav-ity; however, long; neck reconatorc return come ofthe entering kinetic energy back to the grazingflow field. Therefore, the acoustic resistance maybe a function of the length to diameter ratio of theorifice,

2. As chovm in the photographic sequences, atthe crossover from inward to outward flow, flanexists simultaneously inward and outward in dif-ferent parts of the orifice. Thus, no discontinuityin resistance will exist in an osei;latinr syztemwhen the average jet velocity approcuhcz zero fromeither the inflow or outflow directic

3. For long neck resonators, the instantaneousfluid streamlines for oscillatory flow do not, ingeneral, match the steady etreamlires in the nameorifice. Therefore, the acoustic and steady flowresistance do not necessarily correspond.

References

1, Baumoicter, K. J. and Rise, J,: "Visual Ctudy ofthe Effect of Grazing Slow on the OscillatoryFlo,, in a Resonator Orifice," M X-3200, Cept.lO'rb, RAGA.

2. Thurston, G. B„ Hargrove, Jr„ L. E., andCook, W. D„ "Nonlinear properties of CircularOrifices," .wet Acoustics Cocinty of America.Vol, 20, 1967, pp. 9112-1001.

S. Ingard, U. and Icing, H., "Acoustic Nonlinearityof an urifico," Jet Acoustics Society ofAmerica. Vol. 42, IU,17, pp. n-17.

4. I[orsh, A. 0, and Rogers, T., "Fluid mmebmnicalgodol of the Acoustic Impedance, of CmallOrifices," AIM Faper 75-4%, Hampton, ±a.,197,.

,. 7.orumski, W. E. and Pv,rrott, T. L., "NonlinearAcoustic Theory for Rigid loroua 11aterial.o,"'fit D-e19c, June 1971, NAM,

r. Fewer, E., slid Dean, L. W., "Analytical andExperimental Otudies For Predicting Noire At-tenuation in Acoustically Treated Ducto forTurbofan Engineo,." CE-1576 1 Copt. Lars,. IWA.

7. Budoff, :1., and 7.orumaki, W. E., "Pio:r i;ccictancoof perforated Flatco in Tangential cloa," TItX-26ul, uct. 1971, NASA,

0. Rogers, T., and Iferoh, A. G., "The Effect ofGrazing Flow on the Steady Otate Resistance wfCquare-Edged Orifices," AIM leper 7L-406,Hampton, Va., 1975,

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figure 6. -Oscillatory orifice flow regimes with grazing flow.

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Figure 7. - Steady flow into short and long neck resonator cavities.

NASA-Lewis