简介：Atheoreticalmodelingapproachaswellasanunsteadyanalyticalmethodisusedtostudyaerodynamiccharacteristicsofwingflappingwithasymmetricstroke-cyclesinconnectionwithanobliquestrokeplaneduringinsectforwardflight.Itisrevealedthattheaerodynamicasymmetrybetweenthedownstrokeandtheupstrokeduetostroke-asymmetricalflappingisakeytounderstandtheflowphysicsofgenerationandmodulationoftheliftandthethrust.Predictedresultsforexamplesofgivenkinematicsvalidatemorespecificallysomeviewpointsthatthewingliftismoreeasilyproducedwhentheforwardspeedishigherandthethrustisharder,andtheliftandthethrustaregeneratedmainlyduringdownstrokeandupstroke,respectively.Theeffectsofthreecontrollingparameters,i.e.theanglesoftiltedstrokeplane,thedifferentdownstrokedurationratios,andthedifferentanglesofattackinbothdown-andup-stroke,arefurtherdiscussed.Itisfoundthatlargerobliqueanglesofstrokeplanesgeneratelargerthrustbutsmallerlift;largerdownstrokedurationratiosleadtolargerthrust,whilemakinglittlechangeinliftandinputaerodynamicpower;andagain,asmallincreaseoftheangleofattackindownstrokeorupstrokemaycauseremarkablechangesinaerodynamicperformanceintherelevantstroke.

简介：Theeffectsofcorrugationandwingplanform(shapeandaspectratio)ontheaerodynamicforceproductionofmodelinsectwingsinsweeping(rotatingafteraninitialstart)motionatReynoldsnumber200and3500atangleofattack40°areinvestigated,usingthemethodofcomputationalfluiddynamics.Arepresentativewingcorrugationisconsidered.Wing-shapeandaspectratio(AR)oftenrepresentativeinsectwingsareconsidered;theyarethewingsoffruitfly,cranefly,dronefly,hoverfly,ladybird,bumblebee,honeybee,lacewing(forewing),hawkmothanddragonfly(forewing),respectively(ARofthesewingsvariesgreatly,from2.84to5.45).Thefollowingfactsareshown.(1)Thecorrugatedandflat-platewingsproduceapproximatelythesameaerodynamicforces.Thisisbecauseforasweepingwingatlargeangleofattack,thelengthscaleofthecorrugationismuchsmallerthanthesizeoftheseparatedflowregionorthesizeoftheleadingedgevortex(LEV).(2)Thevariationinwingshapecanhaveconsiderableeffectsontheaerodynamicforce;butithasonlyminoreffectsontheforcecoefficientswhenthevelocityatr2(theradiusofthesecondmomentofwingarea)isusedasthereferencevelocity;i.e.theforcecoefficientsarealmostunaffectedbythevariationinwingshape.(3)TheeffectsofARareremarkablysmall:whenARincreasesfrom2.8to5.5,theforcecoefficientsvaryonlyslightly;flowfieldresultsshowthatwhenARisrelativelylarge,thepartoftheLEVontheouterpartofthewingsshedsduringthesweepingmotion.AsARisincreased,ononehand,theforcecoefficientswillbeincreasedduetothereductionof3-dimensionalfloweffects;ontheotherhand,theywillbedecreasedduetothesheddingofpanoftheLEV;thesetwoeffectsapproximatelycanceleachother,resultinginonlyminorchangeoftheforcecoefficients.

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