多相流模型

多相流的介绍：Currentlytherearetwoapproachesforthenumericalcalculationofmultiphaseflows:theEuler-LagrangeapproachandtheEuler-Eulerapproach.TheEuler-LagrangeApproach:TheLagrangiandiscretephasemodelinFLUENTfollowstheEuler-Lagrangeapproach,thisapproachisinappropriateforthemodelingofliquid-liquidmixtures,fluidizedbeds,oranyapplicationwherethevolumefractionofthesecondphaseisnotnegligible.TheEuler-EulerApproach:InFLUENT,threedifferentEuler-Eulermultiphasemodelsareavailable:thevolumeoffluid(VOF)model,themixturemodel,andtheEulerianmodel.1)TheVOFModel:itisdesignedfortwoormoreimmisciblefluidswherethepositionoftheinterfacebetweenthefluidsisofinterest.ApplicationsoftheVOFmodelincludestratifiedflows,free-surfaceflows,filling,sloshing,themotionoflargebubblesinaliquid,themotionofliquidafteradambreak,thepredictionofjetbreakup(surfacetension),andthesteadyortransienttrackingofanyliquid-gasinterface.2)Mixturemodel:Applicationsofthemixturemodelincludeparticle-ladenflowswithlowloading,bubblyflows,sedimentation,andcycloneseparators.Themixturemodelcanalsobeusedwithoutrelativevelocitiesforthedispersedphasestomodelhomogeneousmultiphaseflow.3)ApplicationsoftheEulerianmultiphasemodelincludebubblecolumns,risers,particlesuspension,andfluidizedbeds.离散相模型（离散相的装载率10～12%）求解参数的设定：OptionsforInteractionwithContinuousPhase：Forsteady-statesimulations,increasingtheNumberofContinuousPhaseIterationsperDPMIterationwillincreasestabilitybutrequiremoreiterationstoconverge.UpdateDPMSourcesEveryFlowIterationisrecommendedwhendoingunsteadysimulations;ateveryDPMIteration,theparticlesourcetermsarerecalculated.LengthScale:controlstheintegrationtimestepsizeusedtointegratetheequationsofmotionfortheparticle.AsmallervaluefortheLengthScaleincreasestheaccuracyofthetrajectoryandheat/masstransfercalculationsforthediscretephase.LengthScalefactor:AlargervaluefortheStepLengthFactordecreasesthediscretephaseintegrationtimestep.颗粒积分方法：numerics叶中trackingscheme选项1）implicitusesanimplicitEulerintegrationofEquation23.2-1whichisunconditionallystableforallparticlerelaxationtimes.2）trapezoidalusesasemi-implicittrapezoidalintegration.（梯形积分）3）analyticusesananalyticalintegrationofEquation23.2-1wheretheforcesareheldconstantduringtheintegration.4）runge-kuttafacilitatesa5thorderRungeKuttaschemederivedbyCashandKarp[47].Youcaneitherchooseasingletrackingscheme,orswitchbetweenhigherorderandlowerordertrackingschemesusinganautomatedselectionbasedontheaccuracytobeachievedandthestabilityrangeofeachscheme.Max.Refinementsisthemaximumnumberofstepsizerefinementsinonesingleintegrationstep.Ifthisnumberisexceededtheintegrationwillbeconductedwiththelastrefinedintegrationstepsize.AutomatedTrackingSchemeSelectionprovidesamechanismtoswitchinanautomatedfashionbetweennumericallystablelowerorderschemesandhigherorderschemes,whicharestableonlyinalimitedrange.Insituationswheretheparticleisfarfromhydrodynamicequilibrium,anaccuratesolutioncanbeachievedveryquicklywithahigherorderscheme,sincetheseschemesneedlesssteprefinementsforacertaintolerance.Whentheparticlereacheshydrodynamicequilibrium,thehigherorderschemesbecomeinefficientsincetheirsteplengthislimitedtoastablerange.Inthiscase,themechanismswitchestoastablelowerorderschemeandfacilitateslargerintegrationsteps.IncludingaCoupledHeat-MassSolutionontheParticles：Thisincreasedaccuracy,however,comesattheexpenseofincreasedcomputationalexpense.非稳态跟踪1）连续相稳态离散相非稳态：yousimplyentertheParticleTimeStepSizeandtheNumberofTimeSteps,thustrackingparticleseverytimeaDPMiterationisconducted.WhenyouincreasetheNumberofTimeSteps,thedropletspenetratethedomainfaster.2）连续离散相都为非稳态：Whensolvingunsteadyequationsforthecontinuousphase,youmustdecidewhetheryouwanttoUseFluidFlowTimeSteptoinjecttheparticles,orwhetheryoupreferaParticleTimeStepSizeindependentofthefluidflowtimestep.Withthelatteroption,youcanusetheDiscretePhaseModelincombinationwithchangesinthetimestepforthecontinuousequations,asitisdonewhenusingadaptiveflowtimestepping.随机轨道模型的参数：numberoftries:AninputofzerotellsFLUENTtocomputetheparticletrajectorybasedonthemeancontinuousphasevelocityfield(Equation23.2-1),ignoringtheeffectsofturbulenceontheparticletrajectories.Aninputof1orgreatertellsFLUENTtoincludeturbulentvelocityfluctuationsintheparticleforcebalanceasinEquation23.2-20.Ifyouwantthecharacteristiclifetimeoftheeddytoberandom(Equation23.2-32),enabletheRandomEddyLifetimeoption.YouwillgenerallynotneedtochangetheTimeScaleConstant(CLinEquation23.2-23)fromitsdefaultvalueof0.15,unlessyouareusingtheReynoldsStressturbulencemodel(RSM),inwhichcaseavalueof0.3isrecommended.液滴颗粒碰撞与破碎碰撞：破碎：有两种模型，TAB模型适合低韦伯数射流雾化以及低速射流进入标态空气中的情况。对韦伯数大于100的情况，波动模型适应性较好。在高速燃料射流雾化中，波动模型应用甚广。对于TAB模型，用户需要在y0文本框中设定y0的值。Thedefaultvalue(y0=0)isrecommended.对于Y波动模型，需要输入B0与B1，youwillgenerallynotneedtomodifythevalueofB0,asthedefaultvalue0.61isacceptablefornearlyallcases.Avalueof1.73isrecommendedforB1.颗粒类型中的燃烧类型燃烧（``combusting''）颗粒是一种固体颗粒，它遵从由方程19.2-1所确定的受力平衡、由定律1所确定的加热冷却过程、由定律4所确定的挥发份析出过程（19.3.5节）以及由定律5所确定的异相表面反应机制（19.3.6节）。最后，当颗粒的挥发份完全析出之后，非挥发份的运动、变化由定律6所确定。在SetInjectionPropertiespanel面板中选