fluent中多孔介质模型的设置.docx

fluent中多孔介质模型的设置.docx

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7.19.6UserInputsforPorousMedia

Whenyouaremodelingaporousregion,theonlyadditionalinputsfortheproblemsetupareasfollows.Optionalinputsareindicatedassuch.

1.  Definetheporouszone.

2.  Definetheporousvelocityformulation.（optional）

3.  Identifythefluidmaterialflowingthroughtheporousmedium.

4.  Enablereactionsfortheporouszone,ifappropriate,andselectthereactionmechanism.

5.  Enablethe RelativeVelocityResistanceFormulation.Bydefault,thisoptionisalreadyenabledandtakesthemovingporousmediaintoconsideration（asdescribedinSection  7.19.6）.

6.  Settheviscousresistancecoefficients（  inEquation  7.19-1,or  inEquation  7.19-2）andtheinertialresistancecoefficients（  inEquation 7.19-1,or  inEquation  7.19-2）,anddefinethedirectionvectorsforwhichtheyapply.Alternatively,specifythecoefficientsforthepower-lawmodel.

7.  Specifytheporosityoftheporousmedium.

8.  Selectthematerialcontainedintheporousmedium（requiredonlyformodelsthatincludeheattransfer）.Notethatthespecificheatcapacity, ,fortheselectedmaterialintheporouszonecanonlybeenteredasaconstantvalue.

9.  Setthevolumetricheatgenerationrateinthesolidportionoftheporousmedium（oranyothersources,suchasmassormomentum）.（optional）

10.  Setanyfixedvaluesforsolutionvariablesinthefluidregion（optional）.

11.  Suppresstheturbulentviscosityintheporousregion,ifappropriate.

12.  Specifytherotationaxisand/orzonemotion,ifrelevant.

Methodsfordeterminingtheresistancecoefficientsand/orpermeabilityarepresentedbelow.Ifyouchoosetousethepower-lawapproximationoftheporous-mediamomentumsourceterm,youwillenterthecoefficients  and  inEquation  7.19-3 insteadoftheresistancecoefficientsandflowdirection.

Youwillsetallparametersfortheporousmediuminthe Fluid panel （Figure  7.19.1）,whichisopenedfromthe BoundaryConditions panel （asdescribedinSection 7.1.4）.

Figure7.19.1:

 The Fluid PanelforaPorousZone

DefiningthePorousZone

AsmentionedinSection  7.1,aporouszoneismodeledasaspecialtypeoffluidzone.Toindicatethatthefluidzoneisaporousregion,enablethe PorousZoneoptioninthe Fluid panel.Thepanelwillexpandtoshowtheporousmediainputs（asshowninFigure  7.19.1）.

DefiningthePorousVelocityFormulation

The Solver panelcontainsa PorousFormulation regionwhereyoucaninstruct FLUENT touseeitherasuperficialorphysicalvelocityintheporousmediumsimulation.Bydefault,thevelocityissetto SuperficialVelocity.Fordetailsaboutusingthe PhysicalVelocity formulation,seeSection  7.19.7.

DefiningtheFluidPassingThroughthePorousMedium

Todefinethefluidthatpassesthroughtheporousmedium,selecttheappropriatefluidinthe MaterialName drop-downlistinthe Fluid panel.Ifyouwanttocheckormodifythepropertiesoftheselectedmaterial,youcanclick Edit... toopenthe Material panel;thispanelcontainsjustthepropertiesoftheselectedmaterial,notthefullcontentsofthestandard Materials panel.

Ifyouaremodelingspeciestransportormultiphaseflow,the MaterialName listwillnotappearinthe Fluid panel.Forspeciescalculations,themixturematerialforallfluid/porouszoneswillbethematerialyouspecifiedinthe SpeciesModel panel.Formultiphaseflows,thematerialsarespecifiedwhenyoudefinethephases,asdescribedinSection  23.10.3.

EnablingReactionsinaPorousZone

Ifyouaremodelingspeciestransportwithreactions,youcanenablereactionsinaporouszonebyturningonthe Reaction optioninthe Fluid panelandselectingamechanisminthe ReactionMechanism drop-downlist.

Ifyourmechanismcontainswallsurfacereactions,youwillalsoneedtospecifyavalueforthe Surface-to-VolumeRatio.Thisvalueisthesurfaceareaoftheporewallsperunitvolume（ ）,andcanbethoughtofasameasureofcatalystloading.Withthisvalue, FLUENT cancalculatethetotalsurfaceareaonwhichthereactiontakesplaceineachcellbymultiplying  bythevolumeofthecell.SeeSection  14.1.4 fordetailsaboutdefiningreactionmechanisms.SeeSection  14.2fordetailsaboutwallsurfacereactions.

IncludingtheRelativeVelocityResistanceFormulation

Priorto FLUENT 6.3,caseswithmovingreferenceframesusedtheabsolutevelocitiesinthesourcecalculationsforinertialandviscousresistance.Thisapproachhasbeenenhancedsothatrelativevelocitiesareusedfortheporoussourcecalculations（Section  7.19.2）.Usingthe RelativeVelocityResistanceFormulationoption（turnedonbydefault）allowsyoutobetterpredictthesourcetermsforcasesinvolvingmovingmeshesormovingreferenceframes（MRF）.Thisoptionworkswellincaseswithnon-movingandmovingporousmedia.Notethat FLUENT willusetheappropriatevelocities（relativeorabsolute）,dependingonyourcasesetup.

DefiningtheViscousandInertialResistanceCoefficients

Theviscousandinertialresistancecoefficients arebothdefinedinthesamemanner.ThebasicapproachfordefiningthecoefficientsusingaCartesiancoordinatesystemistodefineonedirectionvectorin2Dortwodirectionvectorsin3D,andthenspecifytheviscousand/orinertialresistancecoefficientsineachdirection.In2D,theseconddirection,whichisnotexplicitlydefined,isnormaltotheplanedefinedbythespecifieddirectionvectorandthe  directionvector.In3D,thethirddirectionisnormaltotheplanedefinedbythetwospecifieddirectionvectors.Fora3Dproblem,theseconddirectionmustbenormaltothefirst.Ifyoufailtospecifytwonormaldirections,thesolverwillensurethattheyarenormalbyignoringanycomponentoftheseconddirectionthatisinthefirstdirection.Youshouldthereforebecertainthatthefirstdirectioniscorrectlyspecified.

Youcanalsodefinetheviscousand/orinertialresistancecoefficientsineachdirectionusingauser-definedfunction（UDF）.Theuser-definedoptionsbecomeavailableinthecorrespondingdrop-downlistwhentheUDFhasbeencreatedandloadedinto FLUENT.NotethatthecoefficientsdefinedintheUDFmustutilizetheDEFINE_PROFILE macro.Formoreinformationoncreatingandusinguser-definedfunction,seetheseparateUDFManual.

Ifyouaremodelingaxisymmetricswirlingflows,youcanspecifyanadditionaldirectioncomponentfortheviscousand/orinertialresistancecoefficients.Thisdirectioncomponentisalwaystangentialtotheothertwospecifieddirections.Thisoptionisavailableforbothdensity-basedandpressure-basedsolvers.

In3D,itisalsopossibletodefinethecoefficientsusingaconical（orcylindrical）coordinatesystem,asdescribedbelow.

Notethattheviscousandinertialresistancecoefficientsaregenerallybasedonthesuperficialvelocityofthefluidintheporousmedia.

Theprocedurefordefiningresistancecoefficientsisasfollows:

1.  Definethedirectionvectors.

·TouseaCartesiancoordinatesystem,simplyspecifythe Direction-1Vector and,for3D,the Direction-2Vector.Theunspecifieddirectionwillbedeterminedasdescribedabove.Thesedirectionvectorscorrespondtotheprincipleaxesoftheporousmedia.

Forsomeproblemsinwhichtheprincipalaxesoftheporousmediumarenotalignedwiththecoordinateaxesofthedomain,youmaynotknowapriorithedirectionvectorsoftheporousmedium.Insuchcases,theplanetoolin3D（orthelinetoolin2D）canhelpyoutodeterminethesedirectionvectors.

（a）  "Snap''theplanetool（orthelinetool）ontotheboundaryoftheporousregion.（FollowtheinstructionsinSection  27.6.1 or 27.5.1 forinitializingthetooltoapositiononanexistingsurface.）

（b）  Rotatetheaxesofthetoolappropriatelyuntiltheyarealignedwiththeporousmedium.

（c）  Oncetheaxesarealigned,clickonthe UpdateFromPlaneTool or UpdateFromLineTool buttoninthe Fluid panel. FLUENT willautomaticallysettheDirection-1Vector tothedirectionoftheredarrowofthetool,and（in3D）the Direction-2Vector tothedirectionofthegreenarrow.

·Touseaconicalcoordinatesystem（e.g.,foranannular,conicalfilterelement）,followthestepsbelow.Thisoptionisavailableonlyin3Dcases.

（a）  Turnonthe Conical option.

（b）  Specifythe ConeAxisVector and PointonConeAxis.Theconeaxisisspecifiedasbeinginthedirectionofthe ConeAxisVector （unitvector）,andpassingthroughthe PointonConeAxis.Theconeaxismayormaynotpassthroughtheoriginofthecoordinatesystem.

（c）  Setthe ConeHalfAngle （theanglebetweenthecone'saxisanditssurface,showninFigure  7.19.2）.Touseacylindricalcoordinatesystem,settheConeHalfAngle to0.

Figure7.19.2:

 ConeHalfAngle

Forsomeproblemsinwhichtheaxisoftheconicalfilterelementisnotalignedwiththecoordinateaxesofthedomain,youmaynotknowapriorithedirectionvectoroftheconeaxisandcoordinatesofapointontheconeaxis.Insuchcases,theplanetoolcanhelpyoutodeterminetheconeaxisvectorandpointcoordinates.Onemethodisasfollows:

（a）  Selectaboundaryzoneoftheconicalfilterelementthatisnormaltotheconeaxisvectorinthedrop-downlistnexttothe SnaptoZone button.

（b）  Clickonthe SnaptoZone button. FLUENT willautomatically"snap''theplanetoolontotheboundary.Itwillalsosetthe ConeAxisVector andthePointonConeAxis.（Notethatyouwillstillhavetosetthe ConeHalfAngle yourself.）

Analternatemethodisasfollows:

（a）  "Snap''theplanetoolontotheboundaryoftheporousregion.（FollowtheinstructionsinSection  27.6.1 forinitializingthetooltoapositiononanexistingsurface.）