REG NASA-TM-X-74018-1977 Low-speed wind tunnel results for a modified 13-percent-thick airfoil.pdf

1、r y-e, _ “-,_,w.,mlllW.lk_,J,rC,i NASA TECHNICAL NASATMX-74018MEMORANDUM(,AsA-T_-x-7401_)Low-sp_._.oWIND_u_._. ,79-2496o_ oc ._suz.Ts Fo. A MoDIFIeDI_-P_RC_-T.ZCK_ A:rRVOIL (NASA) 41 p HC AO3/MF A01 CSCL 01A: m- !llclasO!; _ G3/02 26857li I- LOW-SPEEDWIND-TUNNELRESULTS i “_ FORA MODIFIED13-PERCENT-T

2、HICKAIRFOIL _“ RobertJ.McGheeandWilliamD.BeasleyF:IUif:L“lu/ANahonal Aeronautics andSpace Admm_strahonLangley Research CenterHamPtonV, rgmJa23665 :Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Low-SpeedWind-TunnelResultsi:_ for a Modified13-Percent

3、.ThickAirfoilRobertJ. McGheeandWilliamD. Beasley ,LangleyResearchCenteriL._TSUMMARYiAn investigatlonwasconductedin theLangleylow-turbulencepressuretunnelto evaluate_theeffectson.performanceof modifyinga 13-percent-thicklow-speedairf_o_i_l.Theairfoilcontourwas alteredtoreduce theaft upper-surfacepres

4、suregradientand hencedelayboundary-layerseparationat t_picalclimbliftcoefficientsfor lightgeneralaviationairplanesThe testswerei conducted_ata M_ch numberof 0.15or lessover a Reynoldsnumberrangefromaboutl.Ox lO6 to 9.0x lO6. The geometricangleof attackvariedfromabout-lO to 20.i:!,_, The resultsindic

5、atethat themodificationto theairfoilcontourincreasedithemaximumlift-dragratioabout12 percentat a Reynoldsnumberof 2.0x lO6butthatessentiallyno improvementwas obtainedat Reynoldsnumbersof:il_ 4.0 x lO6 and 6.0x lO6. The resultsalso indicatethatthemodificationtotheairfoil decreasedthemaximumliftcoeffi

6、cientabout0.04 throughouttheReynoldsnumberrangetested. The theoreticalviscousanalysismethodI/If! employedprovedto be a valuabletoolin predictingtheairfoilpressuredis!trlbutionsand boundary-layerseparationpoints.INTRODUCTIONResearchon an initialthicknessfamilyof airfoilsdevelopedfor low-, speedgenera

7、laviationapplicationis reportedin referenceI. ResultsofProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-thisresearchshowedthat the13-percent-thickairfoilprovidedthe bestperformancefor this.i_tial thicknessfamilyof airfoils. This airfoil,whichiis desig

8、natedas theNASA LS(1)-0413airfoil,has beenmodifiedin an attempt ,to furtherimprovethe low-speedperformance. The airfoilcontourwas changed!_ to reducetheaft upper-surfacepressuregradientand hencedelay_boundary-layerseparationat typicalclimblift_oefficientsfor light.generalaviationairplanes. This repo

9、rtpresentstheba-_iclow-speedsection_characteristicsof thismodifiedairfoil-andevaluatestheeffectson performanceresulting_i fromthe changeiD airfoilshape.The investigationwas performedin_tbe_Langleylow-turbulencepressurei.: tunnelat Mach numbersof 0.15 or less. The chordReynoldsnumbervaried_ fromabout

10、l.Ox lO6 to 9.0x l_6 andthe geometricalangleof attackvaried_ fromabout-l_ to 20.i,!SYMBOLSValuesare givenin bothSI andU.S. CustomaryUnits. Themeasurements: andcalculationswere made in theU.S.CustomaryUnits.Cp pressurecoefficient,PL “ Pq_c airfoilchord,centimeters(inches). / cc sectionchord-forcecoef

11、ficient, Cp dcd sectionprofile-dragcoefficient,_ d d(_)wakec pointdragcoefficient(ref.5)dcI sectionliftcoefficient,cn cos _ - cc sin_/ . . -JProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-cm sectionpitching-momentcoefficientaboutquarter-chordPoint,s

12、._. cn sectionnormal-forcecoefficient,- Cp diC,: h v.erticaldistancein wake profile,centimeters(inches)i: M free-streamMach numberi:!p staticpressure,N/m2 (lb/f_t2),_“ q dynamicpressure,N/m2 (Ig/ft2)R Reynoldsnumberbasedon free-streamconditionsandairfoilchordS separationpoint_ t airfoilthickness,cen

13、timeters(inches)x airfoilabscissa,centimeters(inches)z airfoilordinate,centimeters(inches)_ zc mean lineordinate,centimeters(inches)i.“i, zt mean thickness,centimeters(inches)i,! _ geometricangleof attack,degreesii Subscripts:! L localpointon airfoil.i max maximumi. _ undisturbedstreamAbbreviations:

14、LS(1) low-speedfirstseries, Mod modifiedProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-IAIRFOILMODIFICATIONThe airfoilcontourwas changedto reducetheaft upper-surfacepressure %gradient(fig.l) and hencereduceboundary-layerseparationat typicalclimbi:_

15、liftcoefficientsfor lightgeneralaviationairplanes(cI = l.Eto 1.2). Themaximumthicknessratio,trailing-edgethickness,anddesign liftcoefficientI = 0.40)of the originalairfoilwere ret_,ned_ Themodificationto thesurfacecontourof airfoilLS(_)_0413isillustratedin figureI. The uppersurfacemodificationwasacc

16、omplishedbyaddingmaterialfromapproximatelythe2,5 percentchordstationfairingwiththe originalairfoilat the40 percentchordstationand removingmaterial_ from thisstationto theairfoiltrailingedge. The lowersurfacemodifica- .: tionwas accomplishedby addingmaterialfromapproximatelythe50 percentchordstationt

17、o theairfoiltrailingedge. The maximumthicknessof the_,: modifiedairfoilwasmovedforwardabou_,-5-_centchord. Figure2 comparesr_ thechangein mean thicknessandcamberdistributionsfor thetwo airfoils:_ and figure3 comparesthechangesin surfaceslopedistributions.Coordinates: for bothairfoilsaregivenin table

18、sI and II.The theoreticalviscousanalysiscomputerprogramof reference2 wasusedto predictthe pressuredistributionsand boundary-layerseparationpointsfor theairfoils. Boundary-layertransitionwas specifiedat x/c = 0.03forthe theoreticalcalculationsto ensurea turbulentboundary-layerdevelop-ment on theairfo

19、ils. Figure4 showsthetheoreticalresultsforboth airfoilsat Reynoldsnumbersof 2.0x lO6 and4.0 x lO6. At a lift coefficientof 0.40and a Reynoldsnumberof 2.0x lO6 (fig.4(a)bothairfoilsare separationIii_ free. At a liftcoefficientof 1.20the theoryindicatesa decreasein upper-4Provided by IHSNot for Resale

20、No reproduction or networking permitted without license from IHS-,-,-surfaceseparationof about0.05cfor themodifiedairfoil(reduced.pressure_ = 1.20)and a Reynoldsnumbergradient). At thi-ssame liftcoefficient(cIof 4.0 x 106 (fig.4(b)a decreasein separationof _nly about0.02cis “shownfor themodifiedairf

21、oil. Basedon thesetheoreticalresults,improve-I. ments in per-f-o_manceforthemodifiedairfoilat climbliftcoefficientswould be exl_ected, particularly at a Reynolds number of_2.0 x lO6. Since the!.theoreticalmethodis only validforattachedor boup.da_y-layerswith smallamountsof flow separation,themaximum

22、liftcoeffi_for the airfoilscould not be determined from the theory,:_ MODELS,APPARATUS,AND PROCEDURE: ModelsTheairfoil-m_delswere constructedutilizinga metalcore aroundwhich plasticfilland two thinlayersof fiberglasswere used to form thecontourillof theairfoils. The modelshadchordsof 61 cm (24in.)an

23、d spansof_.g-I-.44cm (36in.). Themodelswereequippedwith bothupperand lowersurface_ orificeslocated5.08cm (2 in.)off themidspan. The airfoilsurfacewas,:_ sandedin thechordwisedirectionwith number400 dry siliconcarbidepaperto providea smoothaerodynamicfinish. The modelcontouraccuracywasgenerallywithin

24、+.lO mm (.004in.)._i WindTunnel_ TheLangleylJw-turbulencepressuretunnel(ref.3) is a closed-throat,single-returntunnelwhichcan be operatedat stagnationpressuresfrom l toIO atmosphereswith tunnel-emptytestsectionMach numbersup to 0.42 and 0.22,respectively.Themaximumunit Reynoldsnumberis about49 x lO6

25、 permeterProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-F_L _. (15x 106perfoot)at a Mach numberof about0.22. The tunneltestsectionis 91.44cm (3 ft)v,_deby 228.6cm (7.5ft) high.Hydraulicallyactuatedcircularplatesprovidedpositioningandattach-ment fort

26、he two-dimensionalmodel. The platesare I01.60cm (40in.) inil diameter,rotatewith theairfoil,and are flushwith the tunnelwall._Theairfoilendswere attachedto rectangularmodelattachmentplates (fig.5)and the airfoilwas mountedso that thecenterof rotationof thecircularplateswas at 0.25con themodelreferen

27、ce_line.The air gapsat the tunnelil wallsbetweentherectangularplatesand thecircularplateswere sealedwithflexibleslidingmetal seals,shownin figure5.P.FWake SurveyRake,.rA fixedwake surveyrake (fig.6) at themodelmidspanwas cantilever_ mountedfromthe tunnelsidewalland located,onechordlengthbehindthetra

28、ilingedge of the airfoil. The wake rake utilizedtotal-pressuretub_s_0.1524cm (0.060in.)in diameter,and static-pressuretubes,0.3175cm(0.125in.)in diameter. The total-pressuretubeswere flatteredto O.lOl6cm(0.040in.)for 0.6096cm (0.24in.)from thetip of the tube. The static-;i pressuretubeseach hadfourf

29、lushorificesdrilled900apartand located8i_. tubediametersfromthe tipof the tubeand in themeasurementplaneof thetotal-pressuretubes.InstrumentationMeasurementsof the staticpressureson theairfoilsurfacesand thewakerake pressuresweremade by an automaticpressure-scanningsystemutilizingvariable-capacitanc

30、e-typeprecisiontransducers. Basictunnelpressuresweremeasuredwith precisionquartzmanometers. Angleof attackwas measuredwithfProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-_i p1 a calibrateddigitalshaftencoderoperatedby a piniongear and rackattachedto

31、 thecircularmodelattachmentplates. Data were obtainedby a“ high-speed acquisition system and recorded on magnetic tape. :TESTSAND METHODSii Themodifiedairfoilwas testedat Mach numbersof O.15_.oz_lessover ani angle-of-attackrangefrom about-lO to 20. Reynoldsnumberbasedon thei:! x .airfoilchordwas var

32、iecfromaboutl.Ox lO6 to 9.0 !O6 The airfoilwasi testedbothsmooth (naturaltransition)andwith roughnesslocatedon bothupperand lowersurfacesat 0.075c. The roughnesswas sizedfor eecni:_ Reynoldsnumberaccordingto reference4. The roughnessconsistedof granular-type strips 0.127 cm (0.05 in.) wide, sparcely

33、 distributed, and attached to thei .!.: airfoilsurfacewith clearlacquer.The static-pressuremeasurementsat theairfoilsurfacewere r_duced-tot standardpressurecoefficientsandmachineintegratedto obtain-section!: normal-forceand chord-forcecoefficientsand sectionpitching-momentcoeffi-k “cients about the

34、quarter chord. Section profile-drag coefficient-was computedi:_ from thewake-raketotaland staticpressuresby themethod reportedinreference 5.An estimate of the standard low-speed wind-tunnel boundary corrections(ref.6) amountedto a maximumof about2 percentof themeasuredcoefficientsand these correctio

35、ns have not been applied to the data.PRESENTATIONOF RESULTSThe resultsof this investigationhave beenreducedto coefficientformand are presentedin thefollowingfigures:7fProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I, Figureii.EffectofReynoldsnumbero

36、nsectioncharacteristicsforLS(I)-0413Modairfoil 7_ Comparisonofsectionchaz:acteristicsforLS(I)-0413andi, LS(I)-0413Modairfoils 8_ EffectofReynoldsnumberonchordwisepressuredistributionsF. forLS(1)-0413Modairfoil. 9_i Comparisonof chordwisepressuredistributions-forLS(1)-0413“ andLS(1)-0413Modairfoils l

37、OVariation of .maximumlift coefficient with Reynolds number for_,: LS(I)-0413andLS(I)-0413Modairfoils 11, .ooo.o.i:_ DISCUSSIONi, Theairfoilcontourmodificationproducedthetheoreticallypredicted/_ decreasein aft upper-surfacepressuregradientshownby theexperimentalif pressuredata comparisonforbothairfo

38、ilsin figurelO. Note (fig.lO(a)I_ thatalteringthe shapeof the LS(1)-O413airfoilto reducetheaft upper-i: surfacepressuregradientand retainthe designliftcoefficientof 0.40i, removedthecharacteristicflat-typepressuredistribution.Thus,themodi-fiedairfoilexhibitsa gradualpressurerecoveryof nearlyuniforms

39、lopeover approximately50 percentof theuppersurface. FigurelO(b)showsthedecreasein upper-surfaceboundary-layerseparationat _ = lO and R = 2.0x lO6for themodifiedairfoilas predictedby the viscousanalysismethodofreference2 and discussedunder“AirfoilModification.“Boundary-layer_, separationis indicatedb

40、y the lackof pressuregradienton the uppersurfacenear thetrailingedgeof the airfoils. At o,= lO andR = 4.0x 106,8iProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-F (fig.lO(c)the pressuredistributionsforbothairfoilsindicateess but“ aboutequalamountsof

41、upper-surfacetrailing-edgeseparation. This trendof decreasedseparationat higherReynoldsnumberswas also indicatedby theii, theoreticalmethod. FigurelO(d)comparesthe pressuredata for thetwoi airfoilsat _ _ 16 and R_ 2.0 x IOG. Forthis angleof attackairfoilILS(1)-0413has reachedc and uppersurfacesepara

42、tionextendsfromaboutI Imaxx/c : 0.65to thetrai_ingedge. The LS(I)-0413Mod airfoilis fullystalledLat thisangleof attackand separationextendsfromaboutx/c = 0,25 to theC_ trailingedge This differencein behaviornearstall is attributedto the!_i absenceof the reducedpressure-gradientnear the airfoilmid-ch

43、ordfor the!.modifiedairfoil (Seefig lO(b) This reducedpressure-gradientretards, therapidforwardmovementof upper-surfaceseparationat high anglesof_ attack.The sectioncharacteristicsfor bothairfoilsare comparedi=-figure8forReynoldsnumbersof 2.0 x lO6, 4.0x lO6, and 6.0x lO6. For a Reynoldsnumberof 2.0

44、 x lO6 (fig.8(a)and anglesof attackfromabout40 to 13i_ themodifiedairfoilgeneratesmore liftand lessdragcomparg_totheI originalairfoil. This resultis attributedto lessupper-surfaceseparationii i_ for themodifiedairfoilwith the reducedpressuregradient. Thus,the: lift-curveis more linearat highanglesof

45、 attackcomparedto the lift-curveforthe originalshape An improvementin maximumlift-dragratioof aboutL.12 percentis indicatedfor themodifiedairfoil. However,theangleofattackformaximumliftwas reducedabout30 and hencec decreasedaboutImaxI 0.04 forthemodifiedairfoil The stallcharacteristicsfor bothairfoi

46、ls were similar. At the higherReynoldsnumbers(figs.8(b) and8(c)thecapabilityfor improvementin performanceover that obtainedat R = 2.0x 1069Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-_“ for themodifiedairfoilwas notavailableand thereforenoneoccur

47、red. How-LTever,the sameearlierairfoilstallanddecreaseincI wereexhibited_i m_LXby themodifiedairfo_las was previouslynotedat the lowerReynoldsnumber. _iThe absenceof theimprovementin performancefor themodifiedairfoilat theI_ higherReynoldsnumbersis not surprising,sincethe turbulentboundary-layerii_

48、thicknes_i._decreasedat the highe_Reynoldsnumbersand thereforecan with-standCncreasedpressuregradientsbeforeseparating. FigureII comparesthevaluesof Clmaxfor bothairfoilsfora Reynoldsnumberrangefromaboutt_ 2.0x lO6 to g.o x lO6. Themodifiedairfoilexhibitsa lossin Clmaxof_ about0.04 throughouttheReynoldsnumberrange. The lessnegativevaluesi_i_ of pitching-momentcoefficientsforthe LS(1)-0413Mod airfoilcomparedtotheLS(1)-0413airfoil(fig.8) are associatedwith the reductionin aft_ camberwhichresultedfromalteringthe