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NATIONALADVISORYCOMMITTEEFORAERONAUTICS

TECHNICALNOTE2919

THE ASYMMETRICADJUSTABLESUPERSONICNOZZLE

FOR WIND-TUNNELAPPLICATION

By H. JulianAllen

Ames Aeronautical LaboratoryMoffett Field, Ca.lif.

WashingtonMarch 1953 ‘

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TECHLIBRARYKAFB,NM ~

NATIONALADVISORYCOMKHT’EEFORAERONAUTICS IlllllllllllllllllllllluiCIClbLOllb ~

!CECENICALNOTE2919

TEEMYMMEHUC ADJUSTABLESUPERSONIC

FORWIND-TUNNELAPPLICATION

ByH.JulianAllen

SUMMARY

NOZZLE

Thedevelopmentofanasymmetrictypeofadjustablesupersonicnozzlesuitableforapplicationtowindtunnelsisdescribed.Thisnewtypeofnozzlepermitscontinuousadjustmentofthetest-sectionMachnumberwithouttherequirementof flexiblewalls.Uniformityofflowwithinthetestsectionaswellasthecompressionratiorequiredfortheattainmentofthesupersonicflowareconsidered.

. Theadvantagesanddisadvantagesofthisnozzlerelativeto theconventionalinterchangeable-fixed-blockandflexible-wallnozzlesarediscussed.

.

INTRODUCTION

Inthedesignvelocitystreaminvelocitygradients

ofanywindtunnel,theattainmentofa uniformthetestsectionistheprimeconsideration.Theparallelandnormaltothetest-sectioncenterline

must be smallinorderthattheresultsofaircraftmodeltestsmaybeappliedwithconfidencetothedeterminationofthefree-flightaircraftbehavior.To determinetheeffectsof compressibilityontheaerodynamiccharacteristicsofaircraftmodelsintheconventionaltypeofwindtun-nel,thetest-sectionairspeedmust,inaddition,be adjustable.

In thefamiliarsubsonicwindtunnel,neitheroftheserequirementsisdifficultto obtain.An entrancenozzle,thewallsofwhichprovidea smoothandcontinuouspassagefromtheairentrancethroughtheflat-walledtestsection,willsufficetopreventimportantgradientsnormalto.thetunnelaxis. Ina nonviscousfluid,zeroaxialvelocitygradientsatthetestsectionwouldobtainwithparallelaudflatwallsat thetestsection,butfora realfluidsomeflareofthewallsmustbe providedto

b allowforthegrowthoftheboundarylayeralongthenozzlesurfaces.Withsucha tunnel,thetest-sectionairspeedmaybe veryconvenientlyadjustedby changingtherotationalspeedofthedrivingfanorcompressor.

4

2NACATN 2X9

Withthesupersonicmentsisnotsosimple.wallshapeswillpromote

windtunnel,theattainmentoftheserequire- d

Onlya certainfsmilyof smoothcontinuoustherequireduniformityofflow,while,even k“

moreimportant,thevelocityatthetestse&tioncanno longerbe variedby changingtherotationalspeedofthedrivecompressors.Thislatteranomalymaybe convenientlyshowninthefollowingmanner:

.-Consider

theflowinthe”nozzleoffigure1 wherein.theexitpressurePI maybeloweredwithrespecttotheentrancepressurePo. Sincethemassflowmustbe thesameatianypositionalongthenozzlethen,if-itisassumedthatflowconditionsareconst?nrKacrossaziygivencross-section,

pVA= constant.—

where,atanypoint,

P density

v velocity

A cross-sectionalareanormaltotheflowdirection

Thatis,”.-.

d(pVA)= O

orthelogarithmicderivative

(1)

.- ‘-—

●

_— -——

Bernoullit&equationfor-compressibleflowisgivenby

dp _P - Viv

wherep isthelocalpressure.

Sincethesquareofthevelocityof soundisgivenby—..

dp a2.---=dp

.—

.-

then

dp VdV—. .—P a2 =-M2:

NACATN 2919

andequation(1)becomes

dll dV &,v (1—=-—A

(2)

If thevelocityat allstationsislessthansonic,thenfromequation(2),thefsmiliarresultthatthevelocityincreasesas theareadecreasesisobtained.At supersonicspeeds,when 1-M2 isseentobe negative,thereverseistrue.At thespeedof sound,moreover>1-M2 is zerosothat dA mustbe zero.Thatis,ifa Machnumberofunityisattained,itisonlyattainedat theminimumarea,orthroat,section.

Theflowbehavioras theexitpressurePI isreducedbelow P.isthenthefollowing:Startingfromrest,thevelocitywillincreaseandtillbe a maximumatthethroat.Thisisthefsmiliarconditionwitha subsonicwindtunnel,as shownby curveA offigure1. When PIissufficientlybelowP. tohavethesonicspeedattainedat thethroat(designateda*)as shownby curvesB andC,no furtherreductionin P1 willincreasethethroatvelocityandthenozzleis saidtobe

. “choked.”Instead,a supersonicflowdownstreamof thethroatwillbeobtainedwhichwillbe abruptlyterminatedby one‘ormorecompressionshockwavesnormalto thestream,theaxialpositionofwhichwillbe

. determinedlythepressuredifferenceP. –Pl whichisprovided.Thiscaseis shownby curveC.

Sincetheflowis chokedthenit is clearthataheadof thenormalshockwavethevelocityatanystationisa functiononlyof thelocalareaas itisrelatedtothethroatarea. Thusfora supersonicwindtunnelthespeedat thetestsectionisuniquelydeterminedby theratioofthetest-sectionareatotheminimumor throatareaaheadof it,thepressuredifferenceP.– I?lbeingthatrequiredtomaintainthenormalshockdownstreamofthetestsection.Theratioofareasrequiredasafunctionoftest-sectionMachnumberisshownfora nonviscousfluid(whereintheboundarylayerneednotbe considered)in figure2.,

I1 Thenozzleof figure1 couldprovideanysupersonicspeedrequired

fora modeltestifthemodelweremovedto theappropriatepositiondownstreamofthethroat.Theflow,however,wouldbe unsatisfactorybecauseoftheaxialvelocitygradient.Instead,a passagewithaconcave-walledsectionfollowinga convex-walledsection,suchas showninfigure3, wouldberequired.

To obtaintherequiredspeedat thetestsection,thegeometry.ofthenozzleforwardofthetestsectionmustbe varied(asindicatedby. thedottedcurves)soas to obtaintheproperratiooftest-sectionareatothroatarea,aswellas toprovidesucha passageaswillmeetthe

* requiredzerovelocitygradientsatthemodelposition.Thislatterrequirement,notso simpletoattainas inthesubsoniccase,hasbeen

4 NACATN 2919

classicallytreatedbyPrandtlandJ3tisemanh-employingthemethodofcharacteristics.Applicationofthemethodhasbeenthoroughlytreatedinnumerouspapers.(See,e.g.,refs.lsiiii2.)

Clearly,itiwouldbe possibletodesi&na seriesof interchangeablenozzleshapesoffixedformwhichwouldgiveasmahydifferenttestMachnumbersasdesire-d.Thishadbeentneschemeemployedformanysuper-sonicwindtunnelsbuilttodate. Ithastheadvtitageofisimplicity”butsuffersfromtwomajordisadvantages:First,onlyasmanysupersonictestspeedsareavailableas individtzalfixednozzlessothatifmallspeedincrements,aredesiredthenumberof-nozzlesrequiredbecomeslargeandthecostof suchan installationaccordinglygreat;and,second,forlargewindtunnelstheschemebecomesImpracticalmechanically,sincethenozzleblockweightbecomessogreatas tomakethechangingoftheblockstoodifficultandtimeconsuming.

To avoidthedifficultiesofthefixednozzles,thevariablegeometrynozzlewasdeveloped,With*hisarrangement,as ithasbeenemployedtodate,twoapposite.wallsofthenozzhare rigid,flat,andparallel,whiletheremainingtwowallsaresufficientlythinandflex-ibletobe warped,by a systemof jacks,to-therequirednozzleshapes.Thismethodhastheadvantagesthatanytest-sectionspeedovertheextremitiesof thespeedrsmgemaybe obtainedbyproper.positioningof thejacks,andthechangemaybemadewithoutdismantlingthetumlelas isrequiredwiththeinterchangeablenozzlesyKtem.Of cotise,therearenumerous-disadvantagestothemultijack,f“lexible-wallnozzle.Theflex-iblewallmusthe sufficientlythinasnottooverstresstheplateswhenthewallsareflexedtoencompasstherequiredspeedrange.On theotherhand,tokeepthejackspacingaslargeas~ossibleandsotoreducethenumberof jacksrequired,theplatemustbe maintainedasthickaspos-sibletopreventsaggingorhoggingoftlie>latebetweenjacksduetolocalair-pressuredifferencesacrosstheplateaswellas,ina minordegree,totheweightoftheplateitself.Thushighplatestressesareoccasioned,andhenceoneobjectiontothistypeofnozzleisthatdangerofoverstressing.of theplate(withresultingpermanentsetor structuralfailure)caneasilyoccurby improperjackbperation,necessitatingelaboratesafetydevicestopreventsuchan occurrence.

Thedesignandconstructionofthejackattachmen@to suchahighlystressedplate,theelaboratesysteni-ofjacks,eachofwhichmusthavetheabsoluteminimumofbacklash,theccxnplicationofrequiringpressuresealswhichwillnotrleakandyet%f.11allowmotionoftheplate,thecomplexcontrolsystemforthejacks,andmanyotherfactorsintroducemechanicalcomplexity.TheflexiblenozzleoftheAmesl-by s-footsupersonicwindtunnelshowninfigure4 atteststothisfact.As a resultof thiscomplexity,highcostconstitutesa majorobjectiontotheflexible-wallnozzle.

.

—

—.

.

.-

NACATN2919 ‘5

As is evidentnom theforegoing,neitherthefixed-interchangeablenozzlesystemnortheflexible-wallnozzlemethod,as ithasbeenused,constitutesa solutiontotheproblemof obtaininga suitablesupersonicnozzleforwind-tunnelapplicationsatisfactoryinallrespects.

At theAmesAeronauticalLaboratory,severaluniquemethodsforsolvingthisproblemhavebeendeveloped.It isthepurposeofthispayertodescribeonenewtypeofnozzlethathasbeendevelopedbytheNACAwhich,obviatesmostofthedifficultiesof theoldertypesthathavebeenpreviouslyemployed.

THEASYMMETRICADJUSTABLENOZZLE

A. Silversteinof theFlightPropulsionResearchLaboratoryof theNACA,inan effortto circumventtheundesirablecharacteristicsof theflexible-wallandtheinterchangeablefixed-blocknozzles,proposedwhatisnowtermeda “plugtype”nozzle.Thisnozzle,whichisshowndiagrammaticallyinfigure5, consistsofa trumpet-shapedductinthecenterofwhichis inserteda surfaceofrevolution,theplug. It isclearfromthefigurethat,iftheplugismovedtothepositionA, thecross-sectionalareadecreasesuniformlytothetestsectionandhencetheductwillactas a conventionalnozzlesuitableforvelocitiesupto sonicat thetestsection.WiththepluginpositionB, however,thearea,by properd~ensioningof theductandplug,maybe madea min-imumata stationontheplugforwardof thetestsection.Thetest-sectionMachnumbermaythenbe supersonic,theactualvaluebeingdeyendentupontheTositionof theplugwithintheduct. Of coursetosatisfactorilyusesucha nozzlefora windtunnel,plugandductshapeswouldhavetobe foundwhichwouldgivea test-sectionflowfreeofadversepressuregradients.Unfortunately,it isclearthata viscouswakefromtheplugwilltrailintothetestsectionandpasstheexactpositionthatwould,intheusualcase,be oc’cupiedby themodel.Such

.

a wake,of course,couldnotbe tolerated.

Itwasconsideredthatboundary-layercontrolmightbe,employedto -“--removethewake. To determinewhetherornot,byboundary-layercontrol,thewakeproblemcouldbecircumvented,a two-dimensionalplug-typenozzlewithandwithoutboundary-layercontrolwasinvestigatedexper-imentally.A schlierensystemwasusedtovisualizetheflowandtheresultsoftheinvestigationareshowninfigures6(a)and(b). Infigure6(a)theplug-nozzleflowwithoutboundary-layercontrolisshown.Thewakeisclearly~em as isalsoa shock-wavesystemoriginatingatthetrailingedgeof thetwo-dimensionalplug Itisnotconsideredthattheseshockwavescouldbe preventedbysharpeningthetrailingedge.

6 NACATN 2919

Theeffectupontheflowof introducinga boundary-layersuctionslotisseeninfigure6(b).It isevidentthat,althoughthewakewidthisreduced,it isnota significantuimprovement.Thetrailing-edgeshocks.alsopersist.Moreover,theboundary-layersuctionslotinreducingtheboundary-layerthicknesseffectivelyalterstheplugshapeinsucha wayastocreate–anaddit-iunalcompressionshockattheslot.IftheTlugsurfacewereof’poroysmaterial.soasto allowcontinuousboundary-layerremoval,theflowwouldprobablybe consider-ablyimproved.Neverthelessit isdoubtfu14hata completelysatis-factorynozzleforwind-tunnelapplicationcouldbe developedusingtheplugmethodforspeedcontrolbecauseoftheinherentdisadvantageofhavingtheplugtip directlyupstresmof.thetestposition.

In anefforttorealizetheadvanta~es-cd’theplug-typenozzleand,atthesametime,avoidtheadversepli@wake,theauthorconceivedoftheasyuznetric-nozzleshowndiagrammaticallyinfigure7. L Thelowerwallo&the two-dimensionalarrangementishorizontallytranslatablewithrespecttotheupperwall.Withthelowerwsllmovedforwardtheminimumareaforwardofthetestsectionisdecreasedandthetest-sectionMachnumberaccordinglyincreased,andviceversa.Noproblemofa plugwakearisesforthistypeofnozzleand,presupposingthatwallshapescouldbe formedto giveuniformflowinthetestsectionoverthewholespeedrangeforwhichthenozzlewouldbe employed,sucha nozzlewouldbe satisfactory.Thereremainstheproblemastowhethertheasymmetrywouldpromoteundesirableverticalpressuregradientsofseriousmagnitude.

To~ermitstudiesof theflowthoughsucha nozzle,thetrislnozzleshowninfigure8 wasconstructed.Duringthecourse0$theexperiments,whichwereconductedbyMr.ZegmundBlevissoftheLaboratorystaff,numerousupperandlowercurvedblockswereinvestigated.Side-wallpressuremeasurementsweremadeandschlierenpicturesoftheflowweretakentodeterminetheadequacyofthenozzleconfigurations.

Intheearlystagesof thisinvestigate.cg,thenozzleshayeswerecrudelydeterminedby simplycaniberingsymne.tricalnozzlesthatPrevio~”experiencehadindicatedtobe satisfactory.Inlaternozzles,theflowwas anslyzedby themethodof characteristicstodeterminewhataltera-tionsofnozzlesh~eswouldimprovetheflows.Typicalschlierenflowphotographsof someofthenozzlesinvestigated”’sreshowninfig-uresg(a),(b),and(c). Thenozzleoffigureg(a)gavenearlysatis-factoryflow,whilethat--offigureg(b)(anozzlewhichwasshortenedtomaketheassemblymorecompact)isdefinitelyunsatisfactory,asisevidencedby theshockwaves.Forsatisfactoryflow,Machlinesinthetestsectionshouldbe straightandparallel.To demonstratetheadequacyofa nozzle,inmme casesfinescribelinesweredrawninthe

z,-—

.

—

lItisclearthatthisnozzleis,inessence,one-halfofa two-dimenslonalplug-typenozzle,

NACATN 2919 7

uppersurfaceperpendicularto theflowdirectiontopromotesuchweakshockwavesinthetestsectionasto approximateMachwaves.Theperformanceofa nozzlewithscribemarksisshowninfigure9(c).Theflow,aspredicted.by theMachlines,is seentobe satisfactory.

Somefurtheralterationsweremadeto thenozzlesto improvetheMachnumberrsmgeoverwhichsatisfactoryflowcouldbe obtained.Itwasparticularlydesirabletobe ableto operate,withsatisfactorysupersonicflow,as closetoMachnuniberunityaspossible.Aftersomefurtherrevisions,a minimumsupersonicMachnumber.scmewhatlessthan1.1wasattained.ThemaximumMachnumberforsatisfactoryflowwas2.0. Althoughsomewhathigherspeedscouldbe attained,separationoftheflowwasproneto occuronthelowerwallinthetestsection.

Theseparationofflowwhichoccursonthelowersurfaceisfelttoariseinthefollowingmanner:Tn thecsmberedsectionsofthenozzleupstreamofthetestsection,thepressureat anystationmustbe lowerattheconvexwallthanat theconcavewallinorderthattheflowmaybe turnedalongthecurvedpath. In themainbodyofthestresm,thefluid’isnotinfluencedimportantlyby theviscosityandforthisfluidthecentrifugalforceoneachelementfollowingthecurvedpathiSexactlybalancedby thepressuregradientacrossthenozzle.Theflowinthemainbodyofthestreamisthusnotinfluencedby thefactthatcaniberexists.Theairintheboundarylayermovesata lowervelocitysothatthecentrifugalforceon eachelementisinsufficienttobalancethepressuregradient.Hence,theairwithintheboundarylayeronthesidewallswillmovearoundthepassagewallstowardtheconvexsurface.Theintegratedinfluenceofthecurvature

‘ isthereforeto collecta muchthickerboundarylayerat thedownstreamstationsontheconvexplatethsmontheconcavesurface.ThiS thickerlayeris,of course,moreproneto separationundertheadversepres-suresoccurringinthediffuser.

Itwasapparentfrompressuresurveysalongthewallsofthenozzlethatverticalpressuregradientsoccurredinthetestsectionatthehigherspeeds.Howeverjtheindicationswerethattheseadversegradientswouldnotbe tooseriousup to a Machnumbercloseto2.0.

Theinvestigationofthenozzlewasextendedto determinethecompressionratiorequiredtomaintainsupersonicflowthroughthetestsection.To simulate.as closelyaspossiblea nozzlesuitableforwind-tunnelapplication,thenozzlewasconstructedtopermitthepresenceofa modelsupportgear,showninfigure10,immediatelydownstreamof thetestsection.In orderthatatMachnwbersclose

8 NACATN2919

tounitysucha supporl-gearwouldnotchoketheflowatthepositionofthesupport,thesideandtopwallswereflaredtokeepthecross-sectional.areaatthepositionofthesupport-geargreaterthanthatatthetestsection.This,ofcouxse,incurreda ratherrapiddiver-genceoftheflmedwallsinthissectionof-thediffuser.Thedif-fuserfollowingthesupportgearwasofthefamiliarsubsonictypewitha 3° halfangleofidiffusionat eachwallas a maximum.

b

Thecompressionratiosrequiredtomaintainsupersonicflowweredeterminedwithmd without-thesimulatedmodel-supportgearinstalledandareshowninfigure11. Thepresenceofthesupportgear@rovestheperformanceaswouldbe expectedbecauseOftheflaredwallsoppositethepositiontakenby thesupportgear.TheimprovementduetothepresenceofthesupportgearisprobaQlyalsodue,in-part~tothesupersonicdiffusioncausedby theobliqueshocksystempromotedby thestrutsupport.

Thefactthattherequiredcompressionratiosatthehigher~ch _.numbersisgreaterfortheasymmetricnozzlethanfor.thesymmetricnozzlesconsideredby Crocco(ref.3) isprobablypartlyattributabletotheadverseeffectoftheunusuallythickboundarylayerontheconvexwallofthediffuser.Anotherfactorwhichprobablycontributestothischaracteristicistheflaredsectiontopermitlowsupersonicspeedoperationwiththesupportstrutinplace.Testsofa symmetricnozzlewithsimilarcompensation-forthesupp~rtstruthasalsoshownloweredefficiencyathighMachnumbers.

i.-

Theresultsobtained-fromthetestsofthe1-1/>by l-l/2-inch–modelnozzledemonstratedthatoneofthistypewouldperformsuffi-cientlysatisfactorilyforapplicationtoa largewindtunnel,anditwasdecidedtoemploysucha nozzleintheAmes& by &foot supersonicwindtunnelwhichwastobe constructed.

.-Itwasdeemedadvisable,

however,to furtherinvestigatethenozzleas“amodeloftheproposedoneforthe& by &footwindtunnelusingthelargestsupplyofdry

—

airathighpressuresavailableatthelabor~tory.Accordingly,am&by 8-inch”windtunnelemployingtheasymmetricadjustablenozzlewasconstructed.Thiswindtunnelisshowninfigure12withthesideplatesremovedto showthenozzleshape.Ordinatesfortheloweranduppernozzleblocksaregivenin_tablesI and_II,respectively.p

——. . .———

.2Asregard=thecontinuityofthecurvesbetween0rtiIIahf3) fairnesshasbeendeterminedatAmesAeronauticalLaboratoryusinga simplecurvaturegageconsistingoftwofixedposts_witha thirdmovablepostlocatedmidwaybetweenthe,others.Themovablepostisdirectlyconnectedtoa dialgageto readthedeflectionofthemovable

.—s

relativetothefixedposts.Forthegages..that~ve beenusedin “-the1–by >footand6-by &foot tunnels@ thelaboratory,thefixedpostshavebeenseparatedone-thirty-sixthofthetest-section w

height.Forsucha gage,experiencehasindicatedthattheper-missibledeviationof thecurvaturefromthelocalmeanasmeasured

NACATN 2919 9

Whereaswiththe1-1/2-by l–1/2=inch-modelnozzlethemovableblockwaschangedinpositionmanuallyandbolteddownforeachset-ting,themovingelementof the&by &inch nozzlewasactuatedbyaleadscrewfrom~tsidethenozzle.Leakagethroughthegapbetweenthemovingblockandthesidewallsofthe& by 8-inchtunnelwaspreventedby an inflatablebunarubberseallocatedintheedgesofthemovingelementwhichboreagainstthefixedwalls.

Staticpressuresurveysweremadeusingorificeslocatedinthewallsofthetunnel.TypicaldistributionsofMachnumberfromthebeginningto endofthetestsectionatbothsubsonicandsupersonicspeedsareshownin figure13. It is seenthatoverthefulltest-sectionlength,whichisnearlyequalto thetest-sectiondepth,deviationofMachnumberalongtheaxisis inonecase(M%1.1) aslargeas*2 percent.Fora modelsmallenoughtobe investigatedwithoutwallinterferenceatMachnumbersneartheminimtiof 1.1,themodellengthwillbe oftheorderofhalfthetest-sectionheightforwhichtheMachnumbervariationalongthemodelcanbe kepttoabout*0.~percent.

Surveyswerealsomadeto determinetheverticalgradientsinthetestsectionfromsubsonicto supersonicspeeds.Resultsofa typicalsurveyareshownin figure14 (forthessmeblockpositionsas infig.13)fortheverticaldistributionofMachnumberat a stationnearthecenterofthetestsection.Theverticalgradientsaregen-erallysatisfactoryalthougha gradientispresentatMachnumbersnear1.2and,asnotedpreviouslyforthe1—1/>by l-1/2-inchnozzle,atMachnumbersnear2.0.

CONCLUDINGREMARKS

Theasymmetricadjustablenozzlepossessesseveralmarkedadvan-tagesovertheinterchangeablefixed-blocknozzleandtheflexible-wallnozzle.

Comparedwiththefixed-blocknozzleit IsclearthatthemajoradvantageoftheasymmetricnozzleisthatanyMachnumber(through-outtheattainableMachnumberrange)canbe obtainedby translationofthemovableblock;whereaswiththefixedplates,onlyasmsmyMachnumbersastherearefixednozzlesareavailable.Againjforthe

2(Continued)by thedeflectionofthemovinglegwithreferencetothefixedlegsis0.00@ ofthedistancebetweenthefixedlegs.Forthe&by &inchwindtunnel,thecurvaturevariationwasinvestigatedusinga gagewithfixedposts1 inchapart.Thesurveyshowedthisnozzlesomewhatbelowstandsrdinthat,inat leastoneinstance>a deviationfromthemeanof0.0008inchwasmeasured.

---

—

10 NACATN 2919

fixed-blocknozzleprovidedwithblocksto givemorethantwoorthreeoperatingMachnumbers,thehighcostofthemachinedblockswillmorethanoffsetthecostofthemovableblockdriveendthesealinggearintheasymmetrictype.Finally,forlargewindtunnels,theinter-changingofblocksrequiresunwieldyandexpensiveblock-changinggearaswellasanunnecessarilylongtimetomaketherequiredchanges.

Comparedwiththeflexible-wallnozzleit isevidentthatbecauseofitherelativemechanicalsimplicityoftheasymmetricnozzlethecostof sucha nozzlewillbe considerablylower.A secondadvantageisthatthewallsarerigidandhencemaintaintheiruniformityofcurvatureincontrasttotheflexibleplateswhereinscallopingcanoccurbetweenjack-supportpoints.A third-advantageoftheasymmetrictypeisthatthereislittlepossibilityof structural-@nageto thenozzle.As notedpreviously,structuraldamagecameasilyoccurinflexiblenozzlesdueto improperoperation.ofthejacksalthoughbyproperdesignthisdangercanbe alleviatedtoa largeextent.Finally,withmostoftheflexible-wallnozzlesconstructedtodatethereexiststhepossibilityofexcessivelostmotioninthejackinggearduetorequiredclearanceand,afterconsiderableuse,towear. Hencethereisan everpresentpo~sibilitythattheplateswillnotrepeatedlyflextothepropersettingandso,attheveryleast,thatthecal-ibrationofthenozzlewillnotremainconstant.

Of coursethereareseveraldisadvantagesoftheasymmetricadjustablenozzlein.comparisonwiththeothertwotypes.Ofmostimportanceisthefactthatthecurvatureof theconvexandconcavesurfacesmustbe correctforallspeedsof theoperatingrangesothatcomparedtotheinterchangeableblocknozzleitnecessitatesmuchmorecarefuldesign,andcomparedto theflexible-walltypeitcannotbe convenientlyalteredafteritsconstructioniscompleted.Certainlyitistruethattheasymmetricnozzlessofarinvestigatedhaveshownat someoperatingspeeds~desirablehorizontal-andverticalgradients..Thepresenceof thelatterare-particularlyundesirablesincetheyimplystreamangularity.However,itisconsideredthattheseadversegradientscanbe reducedtoanunimportantscaleby morerefinementof the-nozzleshape.S T@ secondmajordisadvantageoftheasymmetricnozzlessofarstudiedisthattheMachnumberrangeforefficientuseislimitedsince,asnotedpreviously,thecompressionratiosrequiredatthehigherspeedsexceedthatfortheconventionalsymmetricnozzles.Itdoesnotfollowthatsucha characteristicisnecessarilyinherentinthetypehowever.Ithasbeensuggest-edthatthischaracteristicmayresultinpartfrom(a)theeffectoftheflareddiffuserat thepositionof themodelsupport,and(b)theeffectof theasymmetryinthickeningtheboundarylayeroftheEonvexplate.

w

.

.—

-.

—

A

-.

.

—

.—

—

‘Severalimprc5vedmethodsfordesignofasymmetricnozzleshavebeenproposedsincetheoriginalissuanceof thisreport.Themethodofreference4 hasbeenfoundmostusefulandgeneralinap@ication.

.

NACATN 2919 11

Iftheadversecharacteristicresultsfromtheexcessiveflareofthediffuser,it couldeasilybe remediedby employinginsertstoreducethediffusionangleathighMachnumbers.Iftheadversecharacteristicresultsfromthelatter,thesealinthegapbetweenthemovableblockandthesidewallcouldbe removedandtheboundarylayerdrawnoff,by a suitablepump,soas topreventthegrowthoftheexcessivelythickboundarylayeronthetest-sectionfloor.

AmesAeronauticalLaboratoryNationalAdvisoryCommitteeforAeronautics

MoffettField,Calif.,MaY12}194-8

REFERENCES

1. Crown,J. Conrad:SupersonicNozzleDesign.NACATN1651,1948.

2. Puckett,A. E.: SupersonicNozzleDesign.Jour.AppliedMech.Dec.1946,vol.13,no.4,pp.A265-A270.

3. Crocco,Luigi:GallerieAerodinachePerAlteVelocita,L’Aerotecnica.Vol.XV,no.7-8,1935.

—

4. Syvertson,ClarenceA.jad Savin,Raymond:TheDesignofVariableMachNumberAsymmetricSupersonicNozzlesby TwoProceduresIlnployingInclinedandCurvedSonicLines.NACATN 2922,1953.

12 NACATN 2919

SlidePlane

TABLEI.-ORDINATESOFM3VABIELOWERBIOCKOF8-BY8-INCH~L NOZZLE

f?—.— -—. —

L--LI> ~

——-Y..— — .—— ——.

.

.

15.84

Dimensionsininches v.

L

17.Ao18.43019.66020.89222.12223.35324.58325.81427.04428.274

H

9.$349.81g10.36010.819U.18311.444Il.64011.78211..88111.936

L

29.X530.73553.00054.00055.00056.00057.00058.00059.0006Q.00061..000

H

11.974u ●99711.849II..835u.810I-1.770Xl..714U.64011.547n.42011.25$)

.

NACA

*

.

TN 2919 13

TABLEII.-ORDINATESOFFIXEDUPPERBLOCKIN8-BY &-INCHWINIHNINNELNOZZLE

—.— ___T–

—. .— __ __r

HL 9.59

I -4 I I I

0.0001.0002.0003.0004.0005.0006.0007.0008.0009.(NO

10.00011.00012.00013.00014.00015.333~6.5631~.79419.02420.25421.48522.71523.94725.In

DimensiO13S

HL

10.25010.58010●goo11.220I.1.xo11.wo12.07012.33312.56012.77012.97513.lx13.31513.44513.54013.58613.54813.38513.10412.74012.28311.741l-l●17010.608

,,33 -J-rininches

k

26.40827.63828.86830.09931.32932.55933979035.02036.25037.48138.71139994341.17342.40443.63444.86446.09547.32548.55549.78651.01651.33054.99058.660

HL

10.0829.5859●1228.6948.3107=9707.6657.3807.1246.8936.6766.4646.3176.1706.0365.9235.824

5.5915.5855.5615..536

—

NACATN2919

NACATN 2919 15

g

( II

I

.

.

.

Figure 1. - Compressible flow through ocomergent-diverg6ntnozzle.

“1

/6 # -=./

/(

& .8I

/T I

I

<’ .6If

b< I

II

; .4 IT I

I/

.2 I T-

;

E+

Figwe 2.- Ratio of throof io test-section urea for supersonic wind-tunnel nozzles. ~@~

. , . t , .

I

NACATN 2919

Compressionshocks~

17 —

I-

I

/

——.

I.c

Nozzle stition

- -

.

I

\

Figure 3.- Diugrumtypical supersonic

of ve/ocitytihd-tumel

through onozzle.

.

9

18-. .—

NAM”ti%319

.

r

Figure4.–Oneofthe1-by 3-footwind-tunnelflexible-wallnozzlesoftheAmesAeronauticalLaboratory.

1’\

\

d

{

Figure 5.- Silverstein plug-type supersonic nozzle.

20 NACATN 2919

(a)Withoutboundary-layercontrol.

(b)Withboundary-layercontrol.

Figure6.- Schlierenphotographofthe..flowt~.ou@a tw~l~nsi~alplug-typenozzle,

.

.

#

*I

*I

F~xed ~Q,,

/A’/A’////////

ngun?~-Asymmetric t7q@tub/e supersmic nozzle.

/

22 NACATN 2919

,

(a) Modelnozzleassenibled.

.

(b)Modelnozzlewithsideplatesa_@windowsremmed,Figure8.- Thel-1/2-byl-1/2-inchasymmetricadjustablenozzle.

.

NACATN 2919

(a)Nearlysatisfactorynozzle.

(

23

Supersonic.flmnotestablis~d.

M2 1.95.

;upersonicflwlotcompletelyestablished,M = 2.2)

Figure9.-Schlierenphoto~apkofflowthroughanasymmetricadjustablesupersonicnozzleatvariousMachnumbers.

24– T-- NACATN 2919

M2 1.13,

M =1.31,

M % 2.570

M ~ 1.94,

M22. c9.

Supersonicflownotestablished.

.

(b)Unsatisfactorynozzle.

Figure9.-Continued.

P

Supersonicflownotestablished.

M21.34.

M= 1.54.

M = 1.’,-.

M ~ 1.94.

(c)Picturestakenwithsmallindentationsonconcavewall.

Figure9.-Concluded.

—— . . .—-— ------ ... .. -—.—

.

(b)Three+uarterfrontview.

Figure10.–Thel–1/2-byl-1/2–inchasymmetricad~ustablenozzlewithmodelsupportgearinstalled,

.

.

.

Muchwnbe~ M

Figure1/.- Compressionrotiorequiredfor 1+-x /$-inchuqym-. metricoo’’ustublenozzle(oimosphericexit).

28 NACATN 2919

.

“

.

(a)‘lhree+uarterfrontvfew.

.

1

(

(b)Three-quarterrearview.Figure12.- The& by 8-inchwindtunnelwit-hsidewallsremoved.

P NACATN 2919 29

.

.

~ ‘es’‘e’”””o / 2 3 4 5 6 7

Distoncefrom test sectionentrance,inches

Rgure13.- LongitudihulMachnumberdistributionin 8-by 0-inchwindfunnel ~from side-wellmid-heightpressuremeosure-rnenfs).

Much number, At

Figure 14.- Vertical Mach number distribution h 8-@ 8-inch wind tunnel (horn sfde-wall pressure measurements ai station five inches downstream of entrance to

test section ).

. .,