空氣動(dòng)力學(xué)中的動(dòng)名詞解釋

Aerodynamics:somenouns 1Chapter1Typesofflow:Un訐ormFlowSteadyFlowUnsteadyFlowContinuumVersusFreeMoleculeFlowInviscidFlow:p=0ViscousFlow:ijH0IncompressibleFlow:p二constCompressibleFlow:pHconst{SubsonicifMa<1SonicifMa=1SupersonicifMa>1GradientofaScalarField:Thegradientofp,▽p,atgivenpointinspaceisdefinedasavectorsuchthat:1.Itsmagnitudeismaximumrateofchangeofpperunitlengthofthecoordinatespaceatthegivenpoint.2.Itsdirectionisthatofmaximumrateofchangeofpatthegivenpoint.ufenceSAU

DivergenceofaVectorField:Thetimerateofchangeofthevolumewill,ingeneral,amovingfluidelementoffixedmass,perunitvolumeofthatelement,isequaltothedivergenceofVzdenotedby▽?V?CurlofaVectorField:o)isequaltoone-halfofthecurlofV‘wherethecurlofVisdenotedbyVXV.VxV=dxVxV=dxVxMassFlow:ThemassflowthroughAisthemasscrossingApersecond.Letmdenotemassflow?Bodyforces:Gravity,electromagneticforces,oranyotherforceswhich"actatdistanee"onthefluidinsideV.Surfaceforces:PressureandshearstressactingonthecontrolsurfaceS.Theprefectgasequationofstate:P=pRTChapter2Pathlines:WetracethepathofelementAasitmovesdownstreamformpoint,asgivenbythedishedline.SuchapathisdefinedasthepathlineforelementA.Streamlines:Astreamlineisacurvewhosetangentatanypointisinthedirectionofthevelocityatthatpoint.Thedifferencebetweenstreamlinesandpathlines:Ingeneral,streamlinesaredifferentfrompathlines.Youcanvisualizeapathlinesasatime-exposurephotographofafluidelement,whereasastreamlinepatternislikeasingleframeofamotionpictureoftheflow?Inanunsteadyflow,thestreamlinepatternchanges;hence,each"frame"ofthemotionpictureisdifferent.However,forthecaseofsteadyflow,themagnitudeanddirectionofthevelocityvectorsatallpointsarefixed,invariantwithtime.Hence,thepathlinesfordifferentfluidelementsgoingthroughthesame.moreover,thepathlinesandstreamlinesareidentical.therefore,insteadyflow,thereisondistinotionbetweenpathlinesandstreamlines;theyarethesamecurvesinspace.

Vorticity: 4Wedefineanewquantity,vorticity,whichissimplytwicetheangularvelocity.g三23=vxVInavelocityfield,thecurlofthevelocityisequaltothevorticity.Theaboveleadstotwoimportantdefinitions:IfVxVHOateverypointinaflow,theflowiscalledrotational.Thisimpliesthatthefluidelementshaveafiniteangularvelocity.IfVxV=0ateverypointinaflow,theflowiscalledirrotational.Thisimpliesthatthefluidelementshavenoangularvelocity;rather,theirmotionthroughspaceisapuretranslation.Circulation:Thecirculationissimplythenegativeofthelineintegralofvelocityaroundaclosedcurveintheflow.StreamFunction:;v-舛一dx-;v-舛一dx-vr--veVelocityFunction:ufenceSAU

WWV=毀rdQrz~~dzChapter3Bornoulli'sEquationForincompressible、inviscid,steady、rotationalflowwithnobodyforces.19p+-pVz=constalongastreamline乙Forincompressible、inviscid>steady>irrotationalflowwithnobodyforces.p+ipV2=constthroughouttheflow乙Quasi-one-dimensionalcontinuityequationForcompressibleflowPiAiVi=p2A2V2ForincompressibleflowA】％=A2V2Pitot-staticprobeTotalpressurefelthereStaticpressure/felthereTotalpressurefelthere<uurvuJencedAU

Pi+ 2P%=PoStatic dynamic totalPressure pressure pressureConditiononvelocityforincompressibleflowGoverningequationforirrotational,incompressibleflow:Laplace'sequationv24)=002屮02屮d^+d^=0UniformflowAuniformflowisaphysicallypossibleincompressibleflowandthatitisirrotational.InCartesiancoordinates4)=V^x屮=gIncylindricalcoordinates4)=VoorcosG屮=Vgrsin0SourceflowInaincompressibleflowwhereallthestreamlinesarestraightlinesemanatingfromacentralpoint0.Suchaflowiscalledasourceflow?IncylindricalcoordinatesSAUSAU2tttDoubletflowThereisaspecial,degeneratecaseofasource-sinkpairthatleadstoasingularitycalledadoublet.Incylindricalcoordinatesk=ZA

kcos02ttr

ksin02ttrVortexflowConsideraflowwhereallthestreamlinesareconcentriecirclesaboutagivenpoint,assketchedinFigure3.31.Moreover,letthevelocityalonganygivencircu