SECURITY INFORMATION. C!ODV CJAO

RM A51K05.

—

c“—

4 —., .. .

RESEARCHMEMORANDUM-

OBSER.VATIONSOF UNSTEADYFLOW PHENOMENAFOR AN

INCLINEDBODYFITTED WITH STABILIZING FINS

By Merrill H. Mead

Ames AeronauticalLaboratory,Moffett Field. Calif. \

By--------, ~~ND,

. . . . . . . . . . . ... . .. . . . . . . . . . .. .. . . . . . . . .

““”..”~RmD~-~f”OFFICERMAKINGcHAWE}

NATIONALADVISORY COMMITTEE‘ FOR AERONAUTICS

WASHi NGTONJ=mary17,1952

=’/ F 9243

1A.

NACARM A51K03

NATIONALADVISQRYCCMMITTEEFOR

RESEARCHMEMORANDUM

AERONAUTICS

OBSERVATIONSOFUNSTEADYFLOWPHENOMENA

INCIZJKEDBODYFITIEDWITHSTABILIZING

ByMerrilJH.Mead

suMMARY

FORAN

FINS

me variationswithMachnuniberand=@e ofattackof thedynsmicrolling-momentcharacteristicsofa slenderbodyof revolu-tionincombinationwitha cruciformtailhavebeeninvestigatedintheAmes6- by 6-foot supersonicwindtumnel.OscillographrecordsoftheinstantaneousrollingmomentofthemodelwereobtainedforMach

. ntiersof0.90,1.20;1.40,1.53, 1.60, and1.70ata constantfree-stresmReynoldsnumiberof 0.84x 106basedonmaximumbo

%diameter.

Themodelwastestedatanglesofattackof from0°to27 . visul● flowstudiesweremadeof thecross-flowfieldintheregionof the

tailatMachnunibersof1.2,1.4,and1.7 at thesamefree-stresmReynoldsnumber.The“vaporscreentechnique”wasusedfortheflowstudies,andrepresentativephotographsoftheflowfield,obtainedfromthesestudies,arepresented.

Analysisofthedataindicatedthatthemodelbeganto experienceoscillatingrollingmomentsatabout10°angleofattackat-eachMachnumberforwhichtestsweremade,andthatthevariationswithangleofattackoftherollingmomentswere,ingeneral,similarforeachMachnuniber.Throughoutmostoftheangle-of-attackrange,an increaseinMachnumberoscillating

wa;accompaniedby a decreaseinthemagnitudesoftherollingmoments.

I3XT!RODUCTION

Currentemphasisonthedesignofmissilesandsupersonicaircrafthasoccasioneda renewedinterestintheaerodynamiccharacteristicsofbodiesofrevolution.Ofparticularsignificancehasbecomethenature..oftheflowfieldbehindinclinedbodiesofrevolution.Althoughit haS

longbeenrecognizedthatthisflowfielddiffersmarkedlyfromthe. potentiaiflowconsideredby Munk(reference

F

1),thepresenceofvortex..-

-“.---

2 NACARMA51K05

flowintheleeof suchbodieshasonlyrece-ntlymanifesteditselfasa-seriousproblemtothemissileandaircraftdesigner.A recentpaperbyAllenandPerkins(reference2)discussesanqproximaiemethodforestimatingtheforces”andmomentsoninclinedbodiesofrevolutioninwhichtheeffectsofviscosityaretakenintoconsideration.Inthis .paper,thedevelopmentwithdistancealongthebodyoftheviscouscross-flow‘fieldbehindtheinclinedbody%s”r&te”dtothedevelopment :withtimeoftheflowfieldbehinda circularcylindersetinmotiontipulsivelyfromrest. ItWasshownthat,formoderateanglesofattack,thebodyflowfieldcontaineda symmetricallydisposedpairof.vorticeswhichincreasedin strength,andseparatedfartherfromthebody,withdistancedownstream.Theseobsezwations,aswellastheresultsofcircumferentialpressuredistributionsmeasuredat severalstationsalongthebody,wereinqualitativeagreementwiththeresultsof anexperimentalinvestigationmadeby Schwabeinreference3 onthedevelopmentoftheflowfieldbehind& c@cularcylinderimpulsivelyQet.inmotionfrcmrest.Further,itwasshowninreference2 that.as .-thebodyangleofattackincreasedfrcmmoderatetolargevalues,thestrengthof the.vorticesincreasedmorerapidlywithdistancedownstream.Inaddition,itwasnotedthat,a shortdistanceaftoftheogivalnose ~section,thisunstablesymmetrical-pairconfigurationbeganto dischargeas a streetofalternatevorticescharacteristicofthatknowntoexistbehinda circularcylinderintwo-dimensionalflow. ofparticularinterestto thepresentinvestigationwasthelessfamiliarphenomenon,

,

observedduringthetestsreportedinreference2, ofaperiodicrever-—.

salsofthevortex-streetconfiguration.At oneinstant,thestreetofVorticeswassodistributedthatthevortexclosesttothebodywouldappearattheleftside”ofthebody,andat thenextinstanttheentirestreetofvorticeswouldchangesides,thefirstvortexfromthebodythenappearingontheright.Thereversingactionwasapparentlyof anentirelyaperiodicnature,noregularityhavingbeenobservedthroughoutthetests.No explanatioriforthesereversalswasattempted,butitwassuggestedinreference”2that,foraircraftandmissiledesignswhichwouldincorporatelongslenderbodiesofrevolutionwithtailsurfacesattkaft end”andwhichwouldbe expectedtomaneuveratlargeanglesofattack,thedischargeof.avortexstreetandthe developmentof suchareversingactionshouldmanifestitselfasan erraticrollingtendencyas a resultoftheaperiodicasymmetryofforcesonthetailsurfaces.

To investigatethenatureoftherollingmomentsexperiencedby onesuchconfiguration,a body-tailcotiinationhasbeentestedinthe ..-Ames6- by 6-foots~ersonicwindtunnelatMachnumbersrangingfrom “..0.9 to 1.7. Thetestswereperformedtoprovideinformationonthe -effectsofangleofattackandMachnumberonthemagnitudeoftheinstantaneousrollingmomentsinducedona typicalmissileconfiguration.

i

NACARM A51K05 .

TEST

Thetestwasperformed

.

METHODSANDAPPARATUS

WindTunnel

intheAmes6- by 6-footsupersonicwind

3

-. -.

tunnelwhichisa closed-return,variable-pressuresupersonicwindtunnelinwhichtheMachnumbercanbe variedcontinuouslyfrom1.15to1.9whilethetunnelis inoperationandwhichalsocanbe operatedatsubsonicMachnunibersof0.6to 0.93. Thewindtunnelanditsstresmcharacteristicsaredescribedindetailinreference4. Themodelwassupportedinthewindtunnelona conventionalsting-typesupportandwaspitchedin

Themodelnationofbody

thehorizontalplane.

Model

usedin”thepresentinvestigationandcruciformtailtypicalof one

—. ..

consistedof a cotii- .typeofmissiledesign :

currentlybefi studied.Thegeometriccharacteristicsofthemodelare. givenin-figure1. Ofhollowcotistruction,thecylindricalportionof

thebodywasof steel,andtheogivalnoseofaltinum. Steeltailfins,oftriangularplanformandaspectratio4 witha dotile-wedgesection

* 3-percentthick,weremountedattheaftendofthebodyintheverticalandhorizontalplanes.

InstrumentationforForceTests

Themodelwasmountedinthewindtunnelona shortstingextensionwhichwasfittedto theendoftheconventionalsupportsting.Straingageswerelocatedonthestingextensionat twolongitudinalpositions,oneforward.andonerearward.Themodelandstingextensionwererestrainedinrollby a torsion-typespringlocatedinsidethesting.Thestraingsgeson thestingextensionweremountedh sucha mannerthatchangesintheirresistancewouldprovidean indicationofthelateral(yawing)motionsofthemodel(fig.1),whilechangesinresist-anceoftherolling-momentgages,mountedonthetorsionspring,meas”uedtherollingmoments.Forobtainingmeasurementsoftheoscillatingloads,a 2,000cycle-per-secondcarriersystem’wasused. Thissystememployssmamplitude-stabilizedelectronicoscillatortoprovideinputvoltagestothestraingages.Theoutputsofthegagesarepassedthroughan elec-tronicband-passamplifier,theflatpassbandofwhichis800CPSin.widthcenteredaboutthecarrierfrequency.Theoutputofthesmplifier “’isdemodulated,producingsignalsthesmplitudeandfrequencyofwhichreproducethevariationofloadsappliedto thestrain-gagetransducer

4 NACARM A51K05-.

witha maximumerrorof 3 percentoffull-scaledeflection.Theseout-putsignalsarerecordedwitha photographic.mcillographusing *D’Arsonvalelementswhichreproducetheamplitudesofthesignalswitha flatresponsefromO to 160cps,andwhichaccuratelyindicatesignalfrequenciesfromO to500cps. ...

.—.

Staticcalibrationsweremadeofthestraingagesperiodically “ ‘throughoutthetestperiodby thestandardmethodofapplyingknownloadsto themodelandrecordingtheresultingdeflectionsontheoscil-lograph.Itwasfcwndtobe impossible,however,tocalibratethegagesonthestingextensionwiththerequiredaccuracy.Therefore,therecordedoutputsofthesegagesareincludedinthereporttorepresentonlythefrequencyofthelateraloscillations

VisualFlowStudies

ofthemodel...

Inordertoinvestigatethecross-flowfieldaroundthebodyinanattemptto correlatethedevelopmentofthebodyvorticeswiththerecordedvariationsinrollingmoment,usewasmadeof a flowvisual-izationtechnique,describedinreference2,whichhasbeentermedthe*’vapor-screenmethod.~~In thistechnique,a smallamountofwateris

*-

introducedintothewindtunnelwhichresultsinthecondensationofafinefogatthetest,section.

—.A narrowplaneofintenselight,created

by a high-pressuremercury-vaporlamp,ismadeto shineacrossthetests

sectionina plsneessentiallyperpendiculartotheairstream.Inthe —regionsofundisturbedflow,theeffectof the”planeoflightthrOU@the _ ..fogiS to producea uniformlylightedscreenoffogparticles.Inthe.regionof thedisturbedflowaroundthemodel,however,thefogisinhomogeneousandtheflowdisturbancesappe=.onthescreenas ueas ofvaryingbrightness.In thepresenttest,a 16~ camera,mountedonthe.supportsting20 inchesdownstreamofthetailofthemodel,wasusedto

.—

photographthecross-flowfieldas seeninthevaporscreen.Movingpicturesweremadewiththelightscreenintersectingthemodelatapositioncorrespondingtothelocationofthetailonthebody. Themodelwastestedwiththetailremovedforthevapor-screenstudies,inorderthatthecamerahavean&obstructedviewofthebodyflowfieldinthevaporscreen.

TestProcedure. ..-.---

Thetestwasconductedintwophases:theforcetestsonthe-body-tailcombinationfirst;andthevisualflowst-udiesjmadewiththebody

.- .alone,later.Duringthefirstphaseofthetest.progrem,inwhichthemeasurementsweremadeoftheinstantaneousrollingmoments,themodel .

5

wastestedatMachnumbersof0.9, 1.2, 1.4,1.53, 1.6, and1.7 at afree-streamReynoldsnumberof0.84x 10e.basedonmaximumbodydiameter.ThedynsmicpressureincreasedwithMachnuniberfroDI510poundspersquarefootat 1.2to 59opoundspersquarefootat 1.6. Dueto lowertunneltemperatures,thedynamicpressurewas550pounds’persquarefoot ,at1.7Machnumber.Themajority’ofthetestswereperformedintheangle-of-attackrangefrom10°to27°sinceitwasobservedthattherewereno oscillatingrollingmomentsof significantmagnituderegisteredontheinstrumentsfrom0°to 10°angleofattack.Somedratawereobtainedat0°, however,todeterminetheleveloftransientvibrationsrecordedby theoscillograph.ForallMachnunibers,withtheexceptionof0.96datawererecordedat 1° incrementsinqngleofattackthroughoutthe10 to270range.Themaximumanglewaslimitedto 20°inthe0.9Machnunibercasebecauseof excessivemodelVibrations.l

Forthevisualflowstudytests,thetailwasremovedfromthemxlelandreplacedby “acylindricalshellwhichwasfairedin smoothlywiththeforwardportionof thebody. Withthewindtunneloperatingatthesamefree-streamReynoldsnumberas intheforcetests,themodelwastestedatMachnunibersof1.2,1.4,and1.7. At eachMachnumber,themodelangleofattackwasvariedfrom10°to 270whilethecsmerarecordedtheflow patternsformedinthevaporscreen.2 Thephotographsincludedinthisreportareenlargementsof framesfromthesefilms.

RESULTS.

A wideinteresthasrecentlybeenshownintheproblemof erraticrollingmomentsinducedoninclinedbodiesofrevolutionfittedwithtailfinsby theseparatedflowaboutthebody. Inviewofthefactthatlittleinformationon thissub~ecthasbeenpublishedtodate,theresultsofthepresentinvestigationaremadeavailabletothereader,eventhoughtheyareina-verypreliminaryformsndindicatetheneedforfurtherstudyandinstrumentationdevelopment.Thereaderiscautionedtobearinmindthattheresults~e, forthemostpart,qualitative.

1Severelateralvibrationsofthemodelwereobservedduringa ~reviousinvestigationinwhichthebodywiththetailremovedwastestedundersimilarconditiom.It isbelieved,therefore,thatthevibrationsobse~edat thesubsonicMachnumberduringthepresentinvestigationwerenottheresultof fluctuatingforcesonthetail.

‘Severalattemptstoobtainvapor-screenpicturesoftheflowfieldat. 0.9Machnumberwereunsuccessfulbecauseofdifficultiesencountered

inmaintainingtheproperfogdensityinthewhd tunnel.

NACARMnA51K05.

ReproductionsoftypicaloscillographrecordsforthreeMachnwibersanda seriesofauglesofattackare.presentedin figure2.Theuppertraceineachrecordrepresentstherollingmoment,andthetwolowertracesareindicationspfthelateral-motionofthemodel.Inthelattercase,theoutputof’themostrearwardstraingageisrepresentedontheoscillographrecordsby thetracehavingthelargeramplitudesofthetwo. It shouldbe pointedoutthatthesensitivitiesofthetwolateral-motiongagesweremuchgreaterthanthatfortherolling-momentgage;hence,comparisonsofamplitudesoftherolling-momentandyawing-momenttraceshaveno significance.It shouldalsobestatedthattheverticalpositionsoftherolling-momenttracesontheoscillographrecordsarenotindicationsofthestaticrollingmomentsimposedonthemodel.No attemptwasmadeduringthepresentteststomeasurestaticrollingmoments.Thechangesofthepaperspeedcontrolontheoscillograph,whichappearasdifferentspacingsofthetiminglinesfordifferentMachnumbers,didnotvarytheresponsecharacter-isticsof theinstrument.Withtheexceptionofthoseforan sngleofattackof0°,eachrecordisaccompaniedby a photographofthecross-flowfieldatthetailofthebody,obtainedby thevapor-screentech-nique.To facilitateinterpretationofthesephotoraphs,twotypical

5vapor-screenpictures,foranangleofqttackof18 andMachnugbersof1.2- 1.7,arepresentedin figure3 accompaniedbydiagrammaticsketchesofthecross-flowfields.Variationswithangleof attackoftheindicatedlevelsof instantaneousrollingmomentforMachnumbersof0.9,1.2,1.4,1.53,1.6,and1.7 areshowninfigure4. In obtainingthevaluesfortheordinatesofthesecurves,twohorizontallinearenvelopeswerediawnwhichboundedthemajorityofthewavesforeachof““”‘“thetracesof instantaneousrollingmount obtainedfromtheoscillo-graphrecords.The“indicatedlevelof instantaneousrollingmoment”wastakenas one-halfofthedoubleamplitudedefinedby theenvelopes.Inthisplottherollingmomentsarepresentedincoefficientform,basedontailspanandexposedareaofthehorizontaltailsurfaces,andthemagnitudesofthecurvesrepresenta measureof therecordedmomentfluctuationsuncorrectedformechanicalamplification.Thesignificanceofthemechanicalsimplificationisdiscussed

b

DISCUSSION

in thenextsection.

.

.*. .

—

#

.-—’

.

,..

Beforediscussingtheresultsoftheinvestigationinanydetail,itisadvisabletopointouta fewofthefactorsinvolvedin?btainingthedatainorderthatthereadermaybe betterequippedto interpretandevaluatethem. Themodel,asmountedinthewindtunnel,constituteda -springandmasssystemvibratin&torsionally- themodelrepresentingthemass,andtherolling-momentgagerepresentingthespring.Thenatural

.

frequencyoftorsionalvibrationforthesystem-wasde@r@ned experi-mentallytobebetween65 and70 cps. Itwasobservedthatthiswasalso .

-.- -..~.~

NACARM A513S05 7.

thepredominantfrequencyoftherolling-momentvariationsrecorded. duringthetests.Itdoesnotnecessarilyfollow,however,thatthisis

an indicationoftheforcingfrequencyforthesystem,thatis,thefrequencyatwhichthemodelwasreceivingrollingimpulses.Sincethemodelwasessentiallyspringmountedandfreeto oscillate,thenaturalfrequencymightbe expectedtopredominateovera nuniberofpossibleinputfunctions.Forexample,a verylowforcingfrequencyshouldresultinmodeloscillationsat thelowerfrequencywiththenaturalfrequencysuperi~osedas a tr+nsient,whileaperiodicimpulsesmightbe repre-sentedby oscillationsatthenaturalfrequencywithmodulationsappe~- -ingintheamplitudes.

Studiesofallof therecordsobtainedduringthetests,includi~’thosepresentedinfQure 2, indicatea completelyrandomvariationofrolling-momentamplitudewithtime. TherewereveryfewInstancesofsustainedoscillationata constantamplitudesuchaswouldbe expectedfortheconditionofa sinusoidalforcingfunctionof constantsmplitude.Therewere,ontheotherhand,fewinstancesofa modulatedamplitudewhichwouldbe associatedwithaperiodicdisturbances.Furthermore,sincetheamplitudesoftheforcingfunctionswereEnibjecttoanymechanicalamplificationpresentinthevibratingsystem,andsincethis

. amplificationcannotbe determinedwithoutlmuwledgeofthefrequencyoftheforcing@nctionor,foraperiodicdisturbances,thewaveshapeandrisetime,itwasnotpossibletodeterminevaluesoftheforcing-function

. amplitudesfromtheresultsofthepresentinvestigation.

It isclearfromtheaboveconsiderations,tierefore,tkt, becauseofthelimitationsoftheinstrumentationused,theresultsofthepres-enttestsprovidelittleinformationasto thenatureof thedisturbingforcesimposedonthemodelinroll. However,therolUng-momentrecordsobtainedduringthetestsareconsideredsignificantrepresentationsofthevariationsoftherollingmomentsimpartedto themodelbytheseforces.OfparticularinterestwasthemarkedeffectsofMachnuniberandangleofattackontheamplitudesoftherollingmomentsapparentfromaninspectionofthedata. Inordertopresenttheseeffectsina comparisonplot,theattackatfigure4.represent

averageleveloftherolli~-momentamplitudesforeachs&e ofeachMachnumberhavebeenplottedincoefficientforminIt shouldbe emphasizedthattheordinatesofthesecurvesthelevelofoscillationsandnotthemaximumsingle-wavepeaks.

DynamicRollLingMoments

Thedynamicrollingmomentsexperiencedbythemodelduringthe. presenttests,recordsofwhicharereproducedinfigure2, showedasignificanteffectofMachnmiber.Froman examinationoffigure2, itcanbe seenthatforeachangleofattacktheamplitudelevelsofthe ..

8

oscillatingrollingmoments

~

wereofgreatestmagnitudeat

NACARM A531S05

1.2Machnuder,generallylessat M = 1.4,andrelativelysmall.at M = 1.7. —-, .In general,with& therangeofM&h numbersfron-1.2to 1.7,thistrendwasconsistentthroughoutthetests,rolling-momentamplitudelevelsdecreasingwithincreasingMachnuuber.Thepredominantfre-quencyofoscillationof themodelinrollis shownintherecordsoffigure2 tohavebeenbetween65and70 cps,-whichwasthenaturalfre--

.

quencyofthesystemintorsionalvibration,andthesignificanceofwhichhasbeendiscussedpreviouslyIttillalsobe notedfromtherecordsoffigure2 thatthefrequencyoflateralmotionof themmlelwasapproximately13cps,whichwasdete~ned experimentallytobe thenaturalfrequencyoflateralvibrationforthesystem,andthatthisfrequencyisnotapparentinanyof thetypicalrolling-momenttracespresented,norwasit inanyoftherolling-momentdataobtainedthrough-outthetests.Thusapparentlyno interactionexistedbetweenthelateralmotionofthemodelandthemeasuredrollingmoments.The

-.

amplitudelevelsoftheoscillatingrolling-momenttracesoffigure2,..

aswellasthoseforMachnumber’sforwhichtherecordswerenotincludedinthisfigure,areplottedinfigure4 in coefficientformagainstangleofattack.TheinfluenceofMachnumberon themagnitudesoftherolling-momentamplitudesisplainlyevidentinthisfigure.Itcanbe seeninthisfigurethat,as statedpreviously,themagnitudesoftherollingmoments,ingeneral,decreasedwithincreasingMachnu?iber.

._It iS &bO

apparentthatthevariationsofthesmplitudelevelswithangleof .attackwerefairlyconsistentforallsupersonicMachnumbersatwhichte~tswereomade.Ineachcase,peaklevelswererecordedatbetween

.

16 and18 angleofattack,followingwhichtheamplitudesfelloffsharply,thenincreasedagaintoa secondpeak,lowerthanthefirst,at approximately23°.

VisualFlowStudies

Thevapor-screentechnique,whichhasbeenusedinthepresent.

investigationforthevisualizationofthebodyflowfield,isa rel-ativelyrecentdevelopmentinthefieldofvisualflowstudiesandrefinementshaveyettobe madeinitsapplication.Withinitslimi-tations,however,theuseoftheteck”iquehasprovena valuableaidinunderstandingtheoriginoftheirregularitiesintheforcesandmomentsobtainedfromwind-tunneltests.Itwasintendedthattheresultsofthevapor-screenstudiesmadeinconjunctionwiththepresentinvestiga-tionwouldmakeknownthelocationsofthebodyvorticeswithrespecttothetail,anyirregularitiesinthevortexconfigurations,and,throughtheprojectionofthemotionpictures,anydynamicinstabilitieswithintheflowfieldsuchaswereobservedduringthetestsofreference2. “

It shouldbe pointedout,withregardto themotionpictures,that,duetothelimitationsofthephotographicequipmentused,itwasnecessary -’

2A NACARMA51Jf05 9’.

to operatethecameraat therelativelyslowspeedof 4 framesper. secondduringthetestsinorderto obtaintheproperexposure.There

exists,therefore,thepossibilitythatdisturbancesof a veryshortdurationinthevortexpatterncouldhavebeenmissedby thecamera.Itwillslsobe notedfromfigure2 that,inthephotographsfor1.2Machnuniber,thevorticesgenerailya~ear as lJghtareas$whilethoseatMachnumber1.7 aredark.At 1.4Machnuniber,foranglesof attackabove160,thevorticesarealmostobscuredby a darkareawhichapparentlyout~nesthedisturbanceregion,butabovewhichthereappearsa verylightarea. Noexplanationhasbeenfoundtorthesephenomena,buttheyarebelievedtohavehadno relationto therolling-momentoscillations.

A studyofthemotionpicturesofthecross-flowfield,obtainedby thevayor-screenmethod,representativeprintsfromwhicharereproducedinfigure2, indicatedthattheflowfielddidnotdeveloptheexpectedvortexstre~tincross-flowplaneswithintherangeofanglesof attacktested. Conditionsof instabilitywithintheflowfieldwereobserved,however,which,it isbelieved,mayhaveproducedthefluctuationof forcesatthetailresulting-inthemeasuredrollingmoments,evenbeforethevorticeshadbegunsheddingfromthebody.At a Machm.uiberof1.2,foranglesofattackbelow10°,theflowfieldcontaineda symmetricallydis_posedpairofvorticesapparentlystableandlocatedclosetotheb~y. Above u = ‘10°,however,thevortex

. patternrapidlybecsmeunsymmetrical,theleftvortexleavingthebody,risingabove,andcurlingaroundtherightvortex.At 18° angleofattack,an intermittentlateralmotionoftheright(lower)vortexwasobserved.Thevortexa~earedtomoveabruptlyto theright,thentotheleft,aperiodically.Thevorticesdidnotreversepositions,however,aswasobservedinthetestsofreference2. Thisphenomenonwaslessapparentat20°anddisappearedat22°. However,at u = 24°,thecondi-tion!againappeared,andwasvisiblethrougha = 26°. Referringto thecurvesof figure4, it isevidentthatthea~earanceofthismotionintheflowfieldcoincidedcloselywiththeanglesatwhichmaximumrolLingmomentsweremeasuredfor1.2Machnumber.Thephotographsaccompanyingtheoscillographrecordsfor1.2Machmmber infigure2 showtherel-ativepositionsofthevorticesat thevariousanglesofattack,demon-stratingtheasymmetryofthepattern,butobviouslycannotshowthedynsmicinstabilitiesrevealedby themotionpictures.

.

‘Thisobservationpertainsonlytothe~sultsof thetestshereinreported.Discussionswiththeauthorsofreference2 haveindicatedthatfor“amodelwitha cylindricalqfterbody,thenoseshapemayhavea significantinfluenceontheangle-of-attackrangeinwhicha vortex.streetisdischarged. ... . ---

, ...

. . . . . . . ..&,. ;.,

.

.

10 NACARM A51K058

At 1.4Machnumber,—

foranglesofattackbelow10°,thevortexpatternwasmuchtheseineas for1.2Machnumberatthesameangles.However,astheangleofattackwas’increasedabove10°,thevortexpatterbbecameunsymmetricalmuchlessrapidlythanatthelowerMachnumber.Bothvortices,whichhadappearedasrounddots,wereobserved”to elongateverticallyatverynearlythesamerateuntil,at16°,theconfigurationwasonlyslightlyasymmetrical,but,ingeneral,largerthanat 1.2Machnuniber.Aswas”mentionedpreviously,foranglesofattackabove16°,thephotographscontaineda darkareawhichappearedto outlinethedisturbanceregion,andtheindividualvorticeswerenotvisible.Itwasobserved,hwever,thattheoutlineitselfbecamemoreasymmetricalasthe~gle ofattackwasincreasedto27°,andpresumablythiswasassociatedwiththeincreasingunbalanceofthevorticeswithin.NolateralmotionofthevorticeswasvisibleatthisMachnumber,butitisprobablethatifthisconditionhadexisteditwouldhavebeenobscuredinthedarkregionsofthefilm.

Themotionpicturesfor1.7Machnumberprovidesomeexplanationfortheverylowrolling-momentamplitudesmeasuredatthisMachnumberduringtheforcetests.Itwasobservedthatinthiscasethevortexconfigurationremain~dstableandsymmetrical--upthroughnearly20°,andthatevenat a = 27 theasymmetrywasnotnearlyaspronouncedasthatfor1.2Machnuniberandcorrespondinganglesofattack.Further,itwasobservedthatalthoughthefloWfieldwasplainlyvisibleinthemotionpicturesthroughouttheangle-of-attackrange,no fluctuatinglateral .motionsofthevorticesappearedatanytime. Inthephotographsoffigures2(f),2(g),and2(h)for1.7Machnumber,theshockwave,whichisfaintlyvisibleoneithersideofthevortexpattern,isa resultofthecrossflowaroundthebodyhavingexceededthecriticalMachnumber,about0..4forcircularcylinders.(Seereference5.) At anangleofattackcorrespondingtoa cross-flowMachnumberof0.4,theshockwaveemanatesfromthebody;however,asthecross-flowMachnumberisincreased(increasingangleofattack)theshockwavemovesup onthewake,as seeninthephotographs.Althoughthecriticalcross-flowMachnumberwasexceededforeveryfree-streamMachnuniberatwhichthemodelwastestedduringthisinvestigation,theshockwavewasvisibleinthe““vapor-screenpicturesonlyinthesethreeinstances.Whatinfluencetheshockwavehadon thevortexconfigurationsoron theresultingrollingmomentsisnotknown.

CONCLUDINGREMARKS

Althoughtheresultsof thepresentinvestigationareofa prelim-inarynatureonly,andtheinstrumentationhasnotbeensufficientlydevelopedtoprovidequantitativedata,theinformationobtainedfrom

.

thesetestsdoesmibstantiateonesalientfact: thatfortheparticu-larbody-tailconibinationtested,therewasa markedeffectofMach .

NACARM A51X05 11

nuuiberonthemagnitudesoftheoscillatingrollingmomentsofthemodelat anglesofattack.ThemagnitudesoftheoscillationsdecreasedconsistentlywithincreasingMachnumber,withintheMachnuniberrangetested.Also,consideredsignificantwastheconsistencywithwhichthevariationofrolling-momentamplitudeswithangleofattackfollowedsimilartrendsat supersonicMachnumbers.

AmesAeronauticalLaboratory,NationalAdvisoryCommittee

MoffettField,Calif.forAeronautics,

REFERENCES

1. Munk,MaxM.: TheAerodynamicForcesonAirshipHulls.NACARep.184,1924.

2. Allen,H. Julian,andPerkins,EdwardW.: CharacteristicsofFlowOverInclinedBodiesofRevolution.NAcARMA50107,1951..

3. Schwabe,M.: PressureDistributioninNonuniformTwo-Dimensional‘r Flow. NACAT!M1039,1943.

4. Frick,CharlesW.,andO~on,RobertN.: FlowStudiesintheAsymmetricAd@stableNozzleoftheAmes6-by 6-footSupxsonicWindTunnel.NACARMA9E24,1949.

5. Allen, H. Julian:EstimationoftheForcesandMomentsActingonInclinedBodiesofRevolution.NACARMA9126,1949.

c

1 ,J n

I

,●

3.600

__— ——-——— -— ————— ,.—. ———. .—

4 22.,001 I

5Z312 .●

*

Side view of model with toil in ploce

Geometric characteristics

Body fineness ratio: 159 1~Tail aspect ratio: 4.0Noseshope: Ogh +L/4./93

Front view

figure i- Dlogrommotic sketchof mode~

All dimensions in inches

14

4

NACARMA51K05

1- 0./0 Sec

JRo/lingmomentJ M.i g -A b+ C?/OSecYawingmoment

Figure 2.- Compur/sonof hstuntuneousrollhg momentsd three Moth

numbersfor voriousunglesof uttuck

—

. .

.

.

NACARMA51K05 15.

.

*

.

1/?o/lingmomentJ A4=&4Yawingmoment

M.~7

(b) a=/6°

Hgure2.-Continued

16 NACARMA51K05

(C)a=/8°

Figure2.-Continued

.

.

●

.

.-

.

—.

3A NACARMA51K05~

.

.

M=lz

f

Rollingmoment1 M.14Yawingmoment

●

✎

(d)Q=20°

Figure2.- Continued.

17

18 ,

YRo/hg moment~Yffwingmoment

Af”l4

,,

Iill

I?ACARMA51K05.

.

.

M=L7

(e) 0=22”

Figure2.-Continued .

ltMARMA5M05 19

/W”12

Ro//ingmoment-/Yawingmoment-/

I “

.

\

. ii!!M=17

(f) Q=24”

Figure2. -‘ Continued

,.>.

. .

20

[

a

-rRolling moment J a-f.~gYuwhg moment

(9’ Q=26”

Figure2.- Continued

NACARMA5MCO~,

.

=&=-

NACAFMA51KD5

-/”Rolling moment_Yawingmoment

(h’Q=27°

Figure2.- Cone/’uded

-. ..-

I@Or-screen photographVapor-screen phonograph

.

(U]M= /.2(b) M=/. 7

Figure 3.-

I . .

-Diogmmmatic sketch of cross-flow field as represented by vapor-screen photoamnhs-. —r ..-

for 18” angle of offuck ot two Mach numbers.

, ,

I I

Angle of attack, C, o’eg

Figure 4. – Vuritiion of indicated level of mstantonews rolling-moment coefficient

with angle of attack for six Much numbers.

E