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RESEARCHMEMORANDUM”

PREIitMINARYINVESTIGATIONOFA VARIABLE

MASS-FLOWSUPERSONICNKXEINLET ~

ByClydeHayes

LangleyAeronauticalLaboratoryLangleyAir Force Base,Va.

ONAL ADVISORY CommitteeFOR AERONAUTICS

WASHINGTONDecember13, 1949

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AERONAUTICS

PRELIMINARYINVESTIGATIONOFA VARIABLE

MASS+!LOWEX%PERSONICNOSEINLZ?l

By ClydeHayes

●

SUMMARY

A methodhas%eenanalyzedforvaryingthemassflowof supersonicinletshavinga circulsrcrosssectionanda centrslbody. Themethodconsistsofchangingthesizeoftheenteringstreamtubeby meansofan inflatablebootonthesurfaceofthecentrelbody. Testsweremadeat a Machnumberof2.70to determinetheeffectof suchnosesha~s on .theenteringflow,massflow,endpressurerecovery.Comparisonwasmadebetweentheoreticalsndexperimentslmassflows.Thetestresultsshowthatthemassflowcouldbe reducedto 76percentofdesignmassflowtithouta lsrgelossofpressurerecoveryandwithouttheunstableflowconditionsordiscontinuitiesoftheflowthatexistinthefixed–geometrydiffuserswhenshilarreductionsinmassflowsremadebyincreasingthebackpressure.Althoughdragtiasuementswerenotmadeinthisinvestigation,considerationof shockwaveconfigurationsindicatesthattheaccompanyingIncreaseindragissmallerthanthatcausedby thestrongshockwavesaheadoftheinletwhichusuallyaccompanyreductionsinmassflowmadeby increasingthebackpressure.

INTRODUCTION

Fromtheperformancecharacteristicsofrsmjetsoperatingatsupersonicvelocities.itcenbe shownthatforeffectiveoperationovera rsngeofflightconditions,regulationofthemass.flowisdesirable.Fora fixqd+eonmtrysu~rsonicnoseinletofthetypehavinga circularcrosssectionanda centralbodysndhavingpartinternalandpartexternalsupersoniccompression,themass”flowcannotbe reducedwithsupersonicenteringair. Theoreticallyit ispossibleto reducethemassflowby increasingthelackpressureuntiltheintern.slsuprsoniccompressioniseliminatedanda newflowconditionisestablished.This* newflowconditionisestablishedsuddenlysndis accompaniedby enabruptdecreaseofmassflowsndan increaseindrag. Figure1 shows

* thetwoflowconditionsfora fixed~eomtryinletandillustratesthe

2 NACARML9JU

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asymmetrical.flowconditionwhichmayexistdueto unevenseparationonthecentrslbody. Theresultis asymmetricalloadingoftheinlet.Sincethisflowconditionisunstdle,themassflowcannotbe reduced

.&sufficientlywithouttheflowoscillationsandvibrationsbecomingofsuchmagnitudethatthisnwthodcennotcmlinqrilybe used. Themassflowmayalsobe regulatedbymovingthecentrslbodyforwardalongthetis oftheinlet.Sincethecentralbodyusuallyhousesfuel,instrments,smdaccessories,thissystemissorestimesnotdesirable.

Tnthepresentdiscussiona methodis introduced%y whichthemassflowisregulatedby changingthenosean@e ofthecentralbody. Inorderto reducethemassflowenteringtheinlet,theflowmustledeflectedsothatsomeoftheflowdoesnot‘entertheinlqt.Iftheshockwaveproducedby thecentralbodyis eithermadestrongerormovedforwsxd,scmeoftheairwhichwoukdotherwiseentertheinletisdeflected aroundit. By increasingthenosesngleofthecentralbodytheshockwaveismadestrongerand,atthesametime,movesoutward“awayframthelipofthecowling.Thisnaypossiblybe accomplishedbyattachingto thecentralbodya flexiblebootwhichmaybe inflatedtoincreasethenoseangle.Thepurpseofthispreliminaryinvestigationisto determinetheeffectof sucha methodontheenteringflow,massflow,andpressurerecovery,andto comparethee~rimsntalmassflow

.—.

withthetheoretital.. :

ThetestsweremadeattheLa@ey Laboratoryin& intermittent *jetusedforprevioustestsof similarsupersonicinlets.TheMachnwiberwas2.70andtheReynoldsnumber2.~ x 106,basedonthecowl-lipdiameter. —

SYMBOIS —

eb equivalentconeangle;snglebetweenaxisofcliffusersmdline$oiningapexofconeandtangeutto surfaceof inflatedboot

ec semitoneangleofcentrslbody—

ee effectivecme angle;semicomsngleofa centralbodytithaconicshapewhichwouldproducea shockwavetangenttothat

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cowlingpositionpsmmeter;anglebetween~is of diffuserandlinejoiningapexofconeto lipofcowling ,.

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Pf stagnationWessuretier decelerationintoinlet

R radiusofenteringstreamtube

3

DESCRIPTIONOF‘ZEl!!METHOD

Themethodofmass-flowregulationconsideredinthispreliminaryinvestigationconcernsthemriationoftheeffectivenoseangleofthecentralbody. Thiswriationcanbe effectedby theuseofa flexiblebootincorporatedinthesurfaceofthecentrslbody. By inflatingthe ‘boottheeffectivenoseanQe csnbe increased.Thegeneralshapeofsuchaninflatedbootis shownto enexaggeratedscsleinfigure2.Theinflatedportionisnotextendedallthewaytotheapexofthecentrslbodyontheassumptionthatinactualpraoticeitwouldbenecessaryto fastentheflexiblematerislsomedistancebackfromthetip.

Theeffectofthechsngeinnoseangleontheflowis showninfigure3. Withthebootuninflated,theenteringstresmtubeisrepresentedby streamlineBC’.Theradiuso-ftheenteringstreamtubeisshownasR. Asthebootis inflatedtheconeangleis,ineffect,increased,endtheshockwaveOAmovesto a newpositionOAt. Nowthestreamlineunderconsideration,BC,is deflectedatC‘ anddoesnot

. entertheinlet,andno longerrepresentstheenteringstresmtube.StreamlineB~C?’nowrepresentstheenteringstreamtube,slthoughit isalsodeflectedby shockwaveOA?,butata differentpointC“,andenterstheinlet.TheradiusoftheenteringstreamtubeisnowshownasR!,whichis smsllerthanR. Thus,ithasbeenshownthatan increaseofthecentral+odynoseanglewillresultina decreaseinmassflow.

h orderto givesomebasisforcomparingthedataobtainedfromthetests,a pammueterwhichism indicationofthemount of inflationofthebootis introduced.Thisparameter,theequivalentcone-e ‘b,istheanglefommdby theaxisoftheinletanda linedrawnfromthetipofthecentrslbodyandtangenttothes~faceoftheinflatedboot.

Forcomparisonwiththeexperimmtsl datathemassflawenteringtheinletforreducedmas~fbw conditionswascalculatedby assumingthatthecentralbodywasa trueconewiththesemi+pexangleequslto theequivale?rbangle (3b.Theshapesofthestreamlinesinthe

conicelfieldweredraxnfromdatatakenfromreference1, ad the

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comparativesizesoftheenteringstr.eantube.were.de~eminedgraphically.Thismethodgivesonlyenapproximdion~ofthemassflow.Fora moreprecisesolution,notincludedinthispreliminaryinvesti-gation,theflowfieldcanbe calculatedby“applyingthemethodofcharacteristics(reference2) to theexactcentrd-~odynosesha~s.

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APPARATUSANDMODEL

Theapp!mtiususedfortestingandthepethodof acqtiringdataarefullydescribedinreference3. Themassflowwasmeasuredwithacalibratedthinplateorificecontainedina tubeattachedto theremofthemodel. ..

Theentrancedianeterofthecowlingwasl.~0inches,with4° internaland7° externallipangles. .

In orderto simulatetheinflatedbodies,thenoseofthecentralbodywasbuiltupwithsoftsolderandeha~d asfoll.ows:The@dedsolderwasfirstcuttothe~mmn diameter”ofthec=ntrelbodyendthencutto forma conicshapewiththesemi~~x angleequsltotheequivalentconea@e withtheapexofthecpnecoincidentwiththeoriginal“’nose.Thesolderwasthenremovedfromthenosefora dfstanceof1./4Inchhackfromthetip,endtheremainingmaterialwascuttoformafairedcurvealongthesurface.Theresultis-thesham ofthesimulatedbootofthedesiredequivalentengle.TheexactshapewithinthedimensionalMmits givenwasnotconsideredcriticel.Thecentrsl-bodylocationwaskeptconstantatthe~esitionwhichplacedtheshockwavefromthenoseofthecentralbodyatthecowlinglipwitha220centrslbodyata Machnuniberof2.70.

DISCUSSIONANDRESULTS

An analysisoftheflowenteringtheinletwasmadeassumingthattheamx angleofthecentralbodyincreasedbutthatthenoseofthecentrelbodywasstilla truecone. Sincetheinflatedbootwas Istartedsomedistancebackfromthetipofthecentrslbody,theactualshapeisnota cone;therefore,ifthisenalysisistobe usedforthecomparisonofexper~ntaldata,theagreementoftheequivalentcone____me eb withtheeffectiveconeangle ee mustbe determined.TheCOmparhOII Of eb 19nd ee is presentedinfigure4.,andshowsreasonablyclose~eement. Tn figure~,thecalculatedandmeasuredved.qesofmass flowarecomparedintermsofrelativegrossfl~, definedastheratiooftheactualmassflowtothemassflowforthedesigncondition,

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&clu@g thevelueat ‘b = 27.2>,theexper-ntalresultsshowreasonableagreementwiththetheoryassuminga trueconeforthevsluesof ~%. At 27.25°themarkeddeviationfromthetheorymaypossibly%ecausedbytheeffectsoftheappreciabledifferencebetweenthecontourofthecentralbodywiththesimulatedlootandthetrueconicalshawassmnedinthetheory.Onlyatthisvslueof %b dotheeffectsfromexpansionoftheflowoverthe&mlated boot,asobsemedinfigure6,causenoticeablecurvatureoftheshocksheadoftheinlet.

Theeffectofreductionofmassfluwby thismethodonthepressurerecoveryis showninfigure7. Forrelativemassflowof 90 ‘pmcent,thelossofpressurerecoveryfromthevalueof67.7fordesignmassflowisoftheorderof7 ~rcent,whilethatfor80-percentrelativemassflowisoftheorderof9 percent.Forrelativemassflowof76percentthepressurerecoverywasreducedto 56.9. Thesevaluesoflossofpressurerecoveryaresmallenoughto ellowthissystemto bepracticsl.

Shadowgraphsoftheflowconditionpresentedinfigure6 showthattheexternal.flowdoesnotundergosnylargeor abruptchsngeswithchangeof eqtivslentconesingleeb. Thereis sn increaseinthestrengthoftheshockwavewhichindicatesenincreaseindrag,butthisincreaseisgradusl.Thestrengthoftheshockwaveislessthanthatoftheinletwitha normalshockacrosstheentrancesnd,therefore,thedragislessthanifthemassflowisreducedby increasingthebackpressureuntila normslshockwaveisforme~.Thereisno indicationofanyunstableflowconditionswhichmightcauseflowoscillations.

CONCLUSIONS

AmethoQforvaryingthemassflowof supersonicinletshavingacircularcrosssectionanda centrslbodyhas%eenconsidered,andtestsandcalculationshavebeenmadein orderto determinetheeffectsat aMachnumberof2.70of a simulatedinflatablebootonthecentrsl+odysurfaceupontheenteringflow,massflow,and~essurerecovery.Acomparisonwasmadebetweenexperimentalandtheoreticalmassflows.

Thefollowingconclusionsweremade:

1.Themassflowwasdecreasedgraduellyto 76massflowwithan aocompsmyingdecreaseofpressure67.7 percentfordesignmassflowto 56.9 pmcent.

percentof designrecoveryfrom

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2. Themam+flowreductionwasachievedwithoutthenecessityofhavinga movl.ngcentreLbodyandwithouttheunstableflowconditions,~theaccompsz@ngvibrations,andabruptchangeindragproducedby #decreasingthemassflowwith.afixed.~ecmmtryinlet.

3. Formass-fluwreductionsto 76 percentofthedesignmassflowitwasfoundthatthemassflow”andshockanglescouldbe predicted.by

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theoryassumingthecentralbodyto%e representedby a conetangenttotheinflatedboot. .- .

LengleyAeronauticalLaboratoryNationalAdvisoryCommitteeforAeronautics

LangleyAirForceBase,Va.

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1.SteffofComputingSection,,CenterofAm&sis (UhderDirectionof-.

ZdenekKopal):TablesofSupersomlc XlowaroundCones.Tech.Rep. dNo.1,M.I.T.,1947.

2. Ferri,Antonio:ApplicationoftheMethodofCharacteristicstoSupersonicRotationalFlow. NMA Fep.841,1946.

3. Ferri,Antonio,andNucci,LouisM.: TheoreticalandExprimentelAnalysisofLowDragSupersonicInletsHavinga CircularCrossSectionanda CentrslBodyatMachlhuibersof3.30,2.75,and2.45.NACARM*3, 1948.

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Figure 1.-Twoflowconditionsforfixed-geometryMets.(Notto scale.)

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