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1、THEAERONAUTICALJOURNALSEPTEMBER2007571EffectofplungingamplitudeontheperformanceofawindturbinebladesectionM.R.SoltaniandF.RasiMarzabadiSharifUniversityofTechnology,Tehran,IranABSTRACTτdimensionlesstime,τ=t/T()eqequivalentmotionNOMENCLATURE1.0INTRODUCTIONhplungingdispl
2、acement(cm)Hamplitudeoftheplungingmotion(cm)Inmanyengineeringapplications(e.g.helicopters,turbines,compressors),liftingsurfacesexperienceunsteadymotionorarehdimensionlessplungingamplitude,perturbedbyunsteadyincomingflows.Horizontalaxiswindturbinekreducedfrequency,rot
3、orsexperiencelargetimedependentvariationsinangle-of-attackasaresultofcontrolinputangles,bladeflapping,structuralresponsefplungingfrequency(Hz)andwakeinflow.Inaddition,thebladesectionsencounterU∞freestreamvelocity(m/sec)substantialperiodicvariationsinlocalvelocityands
4、weepangle.caerofoilchord(m)Thus,theunsteadyaerodynamicbehaviourofthebladesectionsttime(sec)mustbeproperlyunderstoodtoenableaccuratepredictionsoftheairTperiodofoscillationloadsandaeroelasticresponseoftherotorsystem(1-5).ClliftforcecoefficientTheanalysisofHAWTbladeload
5、sisdividedintotwomajorCdragforcecoefficientareas:dynamicinflowanddynamicstall(6).AtthebladeelementdCmpitchingmomentcoefficientaboutc/4level,thevariouseffectscanbedecomposedintoperturbationstoLEleadingedgethelocalangleofattackandvelocityfield.OneunderlyingTEtrailinged
6、geassumptioninmostaerodynamicmodelsisthattheeffectsofall2Hαangle-of-attack(deg)h=blademotionsandwakeinflowvariationscanbeadequatelyrepre-c·(7-10)αpitchrateπfcsentedbyanequivalentangle-of-attack.However,somek=(11,12)α0meanincidenceangle(deg)U∞studieshavepostulatedthat
7、fundamentaldifferencesexistintheαamplitudeofthepitchingmotion(deg)airloadswhendifferentmodesofmotionareimposed(i.e.pitchingPaperNo.3122.Manuscriptreceived26July2006,revisedversionreceived15February2007,accepted15May2007.572THEAERONAUTICALJOURNALSEPTEMBER2007thesteady
8、stateangles-of-attackrangingfrom–5ºto25ºandinvesti-gationinvolvedtheeffectofoscillationamplitudeonthepressureandaerodynamiccoeffici
