fluent-13.0-workshop06-dpm

CustomerTrainingMaterialWkh6Workshop6UsingtheDiscretegPhaseModel(DPM)IntroductiontoIntroductiontoANSYSFLUENTWS6-1ANSYS,Inc.Proprietary©2010ANSYS,Inc.Allrightsreserved.Release13.0December2010WS6:DiscretePhaseModel(DPM)CustomerTrainingMaterialTutorial•IntroductionandProblemdescription•Mesh•SetupforSinglePhaseSetupforSinglePhase–Models–Materials–BoundaryConditionsBoundaryConditions•SetupforDiscretePhaseModel–ModelsMaterials–Materials–BoundaryConditions•SolverSettingsPti•PostprocessingWS6-2ANSYS,Inc.Proprietary©2010ANSYS,Inc.Allrightsreserved.Release13.0December2010WS6:DiscretePhaseModel(DPM)CustomerTrainingMaterialIntroductionandProblemDescription•ProcessGasandLiquidDropletscomeintoaReactorWewillusetheDiscretePhaseModel(DPM)totracktheLiquid•WewillusetheDiscretePhaseModel(DPM)totracktheLiquidDropletsFhiiihllldlih•Fortheprocess,itisimportantthatonlysmalldropletscomeintotheReactionZone,toavoidblockageinthecatalyst•IfdropletshittheReactorWall,theyrundown–So,itisnotnecessarytotreatthemasdropletsafterhittingthewall–Largerdropletswillberemovedwiththislogicandonlysmallerdropletswillstayinthedomainandpassthroughtotheoutletwhichistheinlettothereactionzone.WS6-3ANSYS,Inc.Proprietary©2010ANSYS,Inc.Allrightsreserved.Release13.0December2010•Theproblemistreatedasisothermal.WS6:DiscretePhaseModel(DPM)CustomerTrainingMaterialMeshOutlet:AmbientPressurePipeWallSymmetrypInlet:V=15m/sD=400mmyyReactorWallD=400mmReactorWallWS6-4ANSYS,Inc.Proprietary©2010ANSYS,Inc.Allrightsreserved.Release13.0December2010WS6:DiscretePhaseModel(DPM)CustomerTrainingMaterialStart-upandMeshModification•LaunchFLUENTrunningDoublePrecisionWewillconverttheTetrahedralelementstoPolyhedralelementstoreducethetotalcellcount(sothesimulationwillproceedmorequickly).Sincepolyhedralcellsarelessdiffusivethantheoriginaltetrahedralcellsdiffusivethantheoriginaltetrahedralcells,thisshouldnotreducetheoverallaccuracy.Taketheoption(seeImage):•Taketheoption(seeImage):–MeshPolyhedraConvertDomainThecellcountisreducedto45,000fromtheprevious101,000WS6-5ANSYS,Inc.Proprietary©2010ANSYS,Inc.Allrightsreserved.Release13.0December2010•Re-displaythemeshtoseetheeffectWS6:DiscretePhaseModel(DPM)CustomerTrainingMaterialSetupSinglePhase(1)•General-•Enablegravity:-9.81m/s²inydirectiontoincludetheeffectofgravitationalforceonthedroplets•Models–TurbulentFlow(Re~400,000*)•EnabletheRealizablek-epsilonModelithEhdWllTtt•withEnhancedWallTreatment•MaterialsPGdtbAi–ProcessGasassumedtobeAirWS6-6ANSYS,Inc.Proprietary©2010ANSYS,Inc.Allrightsreserved.Release13.0December2010*Assumingprocessgasasair@STP,Re=1.225*15*0.4/1.7894E-5=410,752WS6:DiscretePhaseModel(DPM)CustomerTrainingMaterialSetupSinglePhase(2)•BoundaryConditions–Definethe“Inlet“boundary:•Type:VelocityInlet•Velocity:15m/s•TurbulentIntensity:3%•HydraulicDiameter:0.4WS6-7ANSYS,Inc.Proprietary©2010ANSYS,Inc.Allrightsreserved.Release13.0December2010WS6:DiscretePhaseModel(DPM)CustomerTrainingMaterialSetupSinglePhase(3)•BoundaryConditions–Definethe“Outlet“Boundary:•Type:PressureOutlet•GaugePressure:0Pa•BackflowTurbulentIntensity:3%BkflTbltViitRti10•BackflowTurbulentViscosityRatio:10WS6-8ANSYS,Inc.Proprietary©2010ANSYS,Inc.Allrightsreserved.Release13.0December2010WS6:DiscretePhaseModel(DPM)CustomerTrainingMaterialSetupDiscretePhaseModel(1)TheDiscretePhaseModeltracksthemotionofindividual(discrete)particles.Notethatthesameprinciplesapplywhethertheobjectisasolidparticle,orasinthiscase,aliquiddroplet.p,,qpThetrajectoryofeachparticle(droplet)iscomputedoveralargenumberofstepsasitpassesthroughtheflowdomain.Sinceweknowthemassandthesurfaceareaofeachparticleateachstepthesolvercancomputeandthesurfaceareaofeachparticle,ateachstepthesolvercancomputethebalanceofforcesactingonit.Integratedovertheflowdomain,theoveralltrajectorycanbedetermined.Unlikethecontinuousphase(air)wherematerialflowsthroughthegridcells(knownasan‘Eulerian‘referenceframe),theDPMmovesparticleswereeachparticlehasitsownx,y,zco-ordinate(knownasa‘Lagrangian‘referenceframe)referenceframe).Inthiscasetheparticles(droplets)areinert,howevertheDPMdoessupportmuchmorecomplexcaseswheretheparticlesmayevaporateWS6-9ANSYS,Inc.Proprietary©2010ANSYS,Inc.Allrightsreserved.Release13.0December2010and/orcombust.WS6:DiscretePhaseModel(DPM)CustomerTrainingMaterialSetupDiscretePhaseModel(2)•ModelsDiscretePhaseEdit–IncreaseMax.NumberofStepsto50000–KeepStepLengthFactorat5.ppgTheoptionsseenhereare:•“InteractionwithContinuousPhase“–ifthiswasselected(butdonotselectitnow)thiswouldmeanthatthataswellasthe)continuous(air)regioninfluencingtheparticles,theparticleswillalsoinfluencethemomentum/energyoftheair.•“StepLengthFactor“indicateshowmanystepseachparticleshouldmakeacrossagridcell•“MaxNumberofSteps“setsalimitforthenumberofsteps.Sometimesparticlesaretrappedinarecircilationregion,andthisparameterisneededtostopthesolverbeingtrappedinacontinuousloop.Notethatifthisvalueistoosmall,someparticleswillbeterminatedtooearly,beforereachingtheit/ll(hihillbtdhihbtht‘ilt‘)WS6-10ANSYS,Inc.Proprietary©2010ANSYS,Inc.Allrightsreserved.Release13.0De