多相流模型经验谈

1、多相流模型经验谈多相流模型经验谈多相流的介绍：Currentlytherearetwoapproachesforthenumericalcalculationofmultiphaseflows:theEuler-LagrangeapproachandtheEuler-Eulerapproach.TheEuler-LagrangeApproach:TheLagrangiandiscretephasemodelinFLUENTfollowstheEuler-Lagrangeapproach,thisapproachisinappropriateforthemodelingofliquid-liqu

2、idmixtures,fluidizedbeds,oranyapplicationwherethevolumefractionofthesecondphaseisnotnegligible.TheEuler-EulerApproach:InFLUENT,threedifferentEuler-Eulermultiphasemodelsareavailable:thevolumeoffluid(VOF)model,themixturemodel,andtheEulerianmodel.1)TheVOFModel:itisdesignedfortwoormoreimmisciblefluidswh

3、erethepositionoftheinterfacebetweenthefluidsisofinterest.ApplicationsoftheVOFmodelincludestratifiedflows,free-surfaceflows,filling,sloshing,themotionoflargebubblesinaliquid,themotionofliquidafteradambreak,thepredictionofjetbreakup(surfacetension),andthesteadyortransienttrackingofanyliquid-gasinterfa

4、ce.Mixturemodel:Applicationsofthemixturemodelincludeparticle-ladenflowswithlowloading,bubblyflows,sedimentation,andcycloneseparators.Themixturemodelcanalsobeusedwithoutrelativevelocitiesforthedispersedphasestomodelhomogeneousmultiphaseflow.3)ApplicationsoftheEulerianmultiphasemodelincludebubblecolum

5、ns,risers,particlesuspension,andfluidizedbeds.1/7失散相模型失散相的装载率1012%求解参数的设定：OptionsforInteractionwithContinuousPhase：Forsteady-statesimulations,increasingtheNumberofContinuousPhaseIterationsperDPMIterationwillincreasestabilitybutrequiremoreiterationstoconverge.UpdateDPMSourcesEveryFlowIterationisrecom

6、mendedwhendoingunsteadysimulations;ateveryDPMIteration,theparticlesourcetermsarerecalculated.LengthScale:controlstheintegrationtimestepsizeusedtointegratetheequationsofmotionfortheparticle.AsmallervaluefortheLengthScaleincreasestheaccuracyofthetrajectoryandheat/masstransfercalculationsforthediscrete

7、phase.LengthScalefactor:AlargervaluefortheStepLengthFactordecreasesthediscretephaseintegrationtimestep.颗粒积分方法：numerics叶中trackingscheme选项1implicitusesanimplicitEulerintegrationofEquation23.2-1whichisunconditionallystableforallparticlerelaxationtimes.2trapezoidalusesasemi-implicittrapezoidalintegratio

8、n.梯形积分3analyticusesananalyticalintegrationofEquation23.2-1wheretheforcesareheldconstantduringtheintegration.4runge-kuttafacilitatesa5thorderRungeKuttaschemederivedbyCashandKarp47.Youcaneitherchooseasingletrackingscheme,orswitchbetweenhigherorderandlowerordertrackingschemesusinganautomatedselectionba

9、sedontheaccuracytobeachievedandthestabilityrangeofeachscheme.2/7Max.Refinementsisthemaximumnumberofstepsizerefinementsinonesingleintegrationstep.Ifthisnumberisexceededtheintegrationwillbeconductedwiththelastrefinedintegrationstepsize.AutomatedTrackingSchemeSelectionprovidesamechanismtoswitchinanauto

10、matedfashionbetweennumericallystablelowerorderschemesandhigherorderschemes,whicharestableonlyinalimitedrange.Insituationswheretheparticleisfarfromhydrodynamicequilibrium,anaccuratesolutioncanbeachievedveryquicklywithahigherorderscheme,sincetheseschemesneedlesssteprefinementsforacertaintolerance.When

11、theparticlereacheshydrodynamicequilibrium,thehigherorderschemesbecomeinefficientsincetheirsteplengthislimitedtoastablerange.Inthiscase,themechanismswitchestoastablelowerorderschemeandfacilitateslargerintegrationsteps.IncludingaCoupledHeat-MassSolutionontheParticles：Thisincreasedaccuracy,however,come

12、sattheexpenseofincreasedcomputationalexpense.非稳态追踪1连续相稳态失散相非稳态：yousimplyentertheParticleTimeStepSizeandtheNumberofTimeSteps,thustrackingparticleseverytimeaDPMiterationisconducted.WhenyouincreasetheNumberofTimeSteps,thedropletspenetratethedomainfaster.连续失散相都为非稳态：Whensolvingunsteadyequationsforthecont

13、inuousphase,youmustdecidewhetheryouwanttoUseFluidFlowTimeSteptoinjecttheparticles,orwhetheryoupreferaParticleTimeStepSizeindependentofthefluidflowtimestep.Withthelatteroption,youcanusetheDiscretePhaseModelincombinationwithchangesinthetimestepfor3/7thecontinuousequations,asitisdonewhenusingadaptivefl

14、owtimestepping.随机轨道模型的参数：numberoftries:AninputofzerotellsFLUENTtocomputetheparticletrajectorybasedonthemeancontinuousphasevelocityfield(Equation23.2-1),ignoringtheeffectsofturbulenceontheparticletrajectories.Aninputof1orgreatertellsFLUENTtoincludeturbulentvelocityfluctuationsintheparticleforcebalanc

15、easinEquation23.2-20.Ifyouwantthecharacteristiclifetimeoftheeddytoberandom(Equation23.2-32),enabletheRandomEddyLifetimeoption.YouwillgenerallynotneedtochangetheTimeScaleConstant(CLinEquation23.2-23)fromitsdefaultvalueof0.15,unlessyouareusingtheReynoldsStressturbulencemodel(RSM),inwhichcaseavalueof0.

16、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，颠簸模型适应性较好。在高速燃料射流雾化中，颠簸模型应用甚广。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颠簸模型，需要输入B0与B1，youwillgenerallynotneedtomodifythevalueofB0,asthedefaultvalue0.61isacceptablefornearlyallcases.Avalueof1.73isr

17、ecommendedforB1.颗粒种类中的燃烧种类燃烧combusting颗粒是一种固体颗粒，它依照由方程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4/7的挥发份析出过程节以及由定律5所确定的异相表面反响体系节。最后，当颗粒的挥发份完好析出此后，非挥发份的运动、变化由定律6所确定。在SetInjectionPropertiespanel面板中选定WetCombustion选项，用户可以在燃烧颗粒中包含有可蒸发物质。这样，颗粒的可蒸发物质可在挥发份开始析出从前，经历由定律2、3所确定的蒸发与沸腾过程.假设定义的是Combusting燃烧种类颗粒，可在Devola

18、tilizingSpecies下拉列表框下选定由挥发份析出定律4确定的气相组分，参加焦炭表面燃烧反响定律5的气相组摆列于OxidizingSpecies氧化剂组分列表中，有表面反响生成的气相组分那么列于ProductSpecies生成物组分列表中。需要注意的是，对于选定的燃烧颗粒介质，若是燃烧模型为multiple-surface-reaction多表面异相反响模型，那么，由于化学反响计量比在混杂介质中已经被确定，因此OxidizingSpecies与ProductSpecies列表将变灰不可以选。液滴发射种类平面雾化模型的输入地址：在X-,Y-,andZ-Position文本框区可以设定射流

19、的沿直角坐标的三向地址在三维情况下才会有Z-Position出现l速度：在X-,Y-,andZ-Velocity文本框区可以设定射流初始速度沿直角坐标的三向重量在三维情况下才会有Z-Velocity出现l轴的方向仅适用于三维：设定确定喷嘴轴线方向的三个重量，在X-Axis,Y-Axis,andZ-Axis区设定。温度：在Temperature区可设定发射颗粒流的初始颗粒绝对温度。l质量流率：可在FlowRate区设定喷嘴的的颗粒质量流量。l射流连续时间：对于非稳态颗粒追踪计算请参阅19.8节，在StartTime和StopTime区设定发射的开始于结束时间。l蒸气压：设定控制经过喷嘴内部流动的

20、蒸气压表中的pv，在VaporPressure区设定。5/7l直径：设定喷嘴直径表中的d，在InjectorInnerDiam.区设定。l喷嘴长度：设定喷嘴的长度表中的L，在OrificeLength区设定。l内台阶角半径导角半径：设定喷嘴内台阶处的导角半径表中的r，在CornerRadiusofCurv.区设定。喷嘴参数：设定射流角修正系数方程19.4-16中的CA，在ConstantA区设定。CA=3+L/3.6/d,发射角度的大小强烈依赖于喷嘴的内部流动。因此，对于空穴喷嘴，用户设定的CA值应该比单相流的要小才可以。CA的常有取值范围为4.06.0。返流喷嘴的发射角度更小l方向角：设定三

21、维情况下的喷嘴方向开始角与结束角，在AzimuthalStartAngleandAzimuthalStopAngle区设定。压力旋流雾化喷嘴的点属性设定(气体透平工业的人把它称作单相喷嘴simplexatomizer。这种喷嘴，尔后流体经过一个称作旋流片的喷头被加速后，进入中心旋流室。在旋流室内，旋转的液体被挤压到固壁，在流体中心形成空气柱，尔后，液体以不牢固的薄膜状态从喷口喷出，破碎成丝状物及液滴。)l射流角：在SprayHalfAngle区下设定射流发射半角方程19.4-25中的。l压力：在UpstreamPressure区下设定喷嘴上游压力表19.4.1中的p1。液膜破碎常数：设定确定液膜破碎时形成的线状液膜长度的一个经验常数方程19.4-30中的lnb/0，在SheetConstant设定。lnb/0为312的经验常数。这个值必定由用户设定，其缺省值为12withexperimentalsheetbreakuplengthsoverarangeofWebernumbersfrom2to200.线状液膜直径：对于短波，确定液膜破碎波长与线状液膜半径之间的线形比率关系的比率常数，在LigamentConstant区设定。whereCL,ortheligamentconstant,isequalto0.5bydefault.6/7空气辅助雾化喷嘴的点属性设定(