汽车外流场湍流模型与菱形新概念车气动特性的研究

湖南大学博士学位论文汽车外流场湍流模型与菱形新概念车气动特性的研究姓名：吴军申请学位级别：博士专业：车辆工程指导教师：钟志华;谷正气20050420IPIV1ω−kε−k(WholeStressTransportModel--WST)2ε−kω−kε−kε−kIIω−k3F.R.MenterSST4AHMED56IIIAbstractTheaerodynamiccharacteristicsareveryimportanttotheautomobiledynamicperformances,thefuelconsumption,thecomfortandthesafety.Forexample,thedecreaseoftheaerodynamicdragforcecoefficientwhichisproportionaltothesquareofthevelocitycangreatlyreducethefuelconsumptionespeciallyatthehighspeed.Thevehiclestabilityinthelateralwindisalsoacrucialguidelineforthevehiclesafetyperformanceespeciallyatthehighspeed.Becausetheseparatedflowandturbulencebehindtheautomobilehavegreateffectontheautomobileaerodynamics,thepreciseturbulencemodelfortheaccuratesimulationoftheautomobileaerodynamiccharacteristicshasbecomethemostdifficultproblemandkeystoneinthesimulation.Theturbulencemodelsappliedinthetraditionalsimulationoftheautomobileexternalflowfieldarecommonlybasedonthe“general”condition.Infact,theautomobileexternalflowfieldhassomedifferentaspectsfromthe“general”condition.So,amoresuitableturbulencemodelshouldbedevelopedbasedonthepropertyoftheautomobileexternalflowfield.Fromthetheoryaspect,anewturbulencemodelhasbeendevelopedbasedonRSMequationscombiningtheanalysisofnear-wallasymptoticbehaviorintheautomobileexternalflowfieldwiththetensortheoryandlow-Remodification.Fromthecalculation,theaerodynamicssimulationsofthenewconceptvehicleandthetraditionalcargetthedragandliftcoefficientsandotherresultsbasedonthenewlydevelopedturbulencemodel.Fromtheexperiment,theaerodynamicsofthenewconceptvehiclehasbeeninvestigatedbythePIVandthewind-tunnelexperimentwhichverifythesimulationresults.Inparticular,thefollowingworkincludingtheinnovationhasbeencompleted:1.Summarizethedomesticandinternationalresearchanddevelopmentstatusoftheautomobileexternalflowfieldnumericalsimulation.Forthefirsttime,anewLRNLEVM(low-ReNonlinearEddyViscosityModel)isbroughtforwardbasedonthepropertyoftheautomobileexternalflowfield.Inthemodelingprocess,theEASM(ExplicitAlgebraicStressModel)includingthedetailedmechanismoftheIVoriginalaccurateReynoldsStressModelisdeducedbasedonthesimplifiedReynoldsStressTransportEquations.ThentheLow-RemodificationontheEASMiscarriedoutbythemethodofnear-wallanalysis.Finallybycombiningω−kandε−kmodels,thewholeLRNLEVMbasedonthetwo-equationisdevelopedandnamedasWST(WholeStressTransportModel).2.Differentfromthelineareddyviscosityturbulencemodelsoftenusedintheautomobileengineeringsuchasε−k,WSTmodelconsidersmoredetailedmechanismofthelow-ReStressModelandcombinestheadvantagesofω−kandε−k.WSTcanreflecttheanisotropismoftheReynoldsstressinthenear-wallandturbulenceflowinthefarfield.Inaddition,WSTisverygoodtobeusedinthenumericalsimulationoftheautomobileexternalflowfieldbecauseWSTdoesnothavetosolvesixequationsofReynoldsstressandcostslesstime.3.WSTmodelhastwoimprovementscomparingwithtotheSSTmodel(F.R.Menter).Firstly,WSTmodeldoesconsidernotonlytheeffectoftheshearstressbutalsothenormalstress.Secondly,WSTmodeldoesnothavetochangetheeddyviscositycoefficientsbetweenthenear-wallandfarfield.4.Thenewmodelhasbeenverifiedandappliedonfourtypicalflows.Thetestcasesincludechannelflow,2Dsteadyseparatedflow,stepbackwardflowandAhmedmodelflow.ThecomputationresultsshowthatthenewmodelhasanoverallgoodperformancecomparingwiththeresultofexperimentandDNS.5.Bythesimulationofthevelocityvector,theturbulencekineticdistributionandthestreamlineatthedifferentcrosssectionsbehindtheautomobile,ithasbeenrevealedwhytherhombusnewconceptvehiclegetslowerdrag.6.Inthewindtunnelexperiment,wesucceedgettingtheeffectoftheReynoldsnumberandthewindtunnelboundarylayerontheautomobileaerodynamics.Combiningthewindtunnelexperimentwiththenumericalsimulation,theaerodynamicforce,momentandpressurecoefficientinthesymmetryplanofthenewconceptvehicleandthetypicalcarhasbeencarriedout.Thesimulationresultsshowgoodagreementwiththeexperiment.Finallytheaerodynamiccharacteristicsofthenewconceptvehicleareoptimizedbythedesignofthelatterinterceptor.Keywords:Automobile,Externalflowfield,Turbulencemodel,Numericalsimulation,Newconceptvehicle,Windtunnelexperiment1______2V1.164.1694.2694.3704.4704.5714.6ab724.7724.8734.9744.10u744.11''vu744.122u'754.132'ν754.13764.15764.164774.17AHMED794.18AHMED794.1925o()35o804.2025oAHMED804.2135oAhmedε−k814.2235oAhmedSST814.2335oAhmedSSG824.2435oAhmedWST824.2525oε−k834.2625oSST834.2725oSSG844.2825oWST844.29AHMED854.30AHMED85VI4.31AHMED864.32AHMED865.1KD-03895.2895.3915.4935.5PIV945.6965.7975.8985.9995.101005.111015.121015.131015.141025.151055.161055.171065.181065.191075.201075.211085.221095.231095.241105.25321105.261105.27321115.281115.29PIV1125.301135.311135.32PIV114VII5.331145.341155.351165.361165.371175.381175.391185.401195.411195.421205.431206.11226.21236.31236.41236.51246.61256.71256.81266.91266.101286.111286.121296.131296.141306.151307.1PIV1327.21337.31337.41347.51347.61357.71357.8PIV136VIII7.91367.101377.111377.121387.131397.141397.151397.161397.171407.181407.191407.201407.211417.221417.231417.241417.251427.261427.271437.281437.291437.301437.311447.3214