简介：Theabsenceofsub-gridscale(SGS)motionsleadstosevereerrorsinparticlepairdynamics,whichrepresentsagreatchallengetothelargeeddysimulationofparticle-ladenturbulentflow.Inordertoaddressthisissue,datafromdirectnumericalsimulation(DNS)ofhomogenousisotropicturbulencecoupledwithLagrangianparticletrackingareusedasabenchmarktoevaluatethecorrespondingresultsoffilteredDNS(FDNS).ItisfoundthatthefilteringprocessinFDNSwillleadtoanonmonotonicvariationoftheparticlecollisionstatistics,includingradialdistributionfunction,radialrelativevelocity,andthecollisionkernel.Thepeakofradialdistributionfunctionshiftstothelarge-inertiaregionduetothelackofSGSmotions,andtheanalysisofthelocalflowstructurecharacteristicvariableatparticlepositionindicatesthatthemosteffectiveinteractionscalebetweenparticlesandfluideddiesisincreasedinFDNS.Moreover,thisscaleshiftinghasanobviouseffectontheodd-ordermomentsoftheprobabilitydensityfunctionofradialrelativevelocity,i.e.theskewness,whichexhibitsastrongcorrelationtothevarianceofradialdistributionfunctioninFDNS.Asawhole,theradialdistributionfunction,togetherwithradialrelativevelocity,cancompensatetheSGSeffectsforthecollisionkernelinFDNSwhentheStokesnumberbasedontheKolmogorovtimescaleisgreaterthan3.0.However,itstillleavesconsiderableerrorsforStk<3.0.

简介：Fortwo-dimensionnonlinearconvectiondiffusionequation,atwo-gridmethodofcharacteristicsfinite-elementsolutionwasconstructed.Inthismethodthenonlineariterationsisonlytoexecuteonthecoarsegridandthefine-gridsolutioncanbeobtainedinasinglelinearstep.Forthenonlinearconvection-dominateddiffusionequation,thismethodcannotonlystabilizethenumericaloscillationbutalsoacceleratetheconvergenceandimprovethecomputationalefficiency.Theerroranalysisdemonstratesifthemeshsizesbetweencoarse-gridandfine-gridsatisfythecertainrelationship,thetwo-gridsolutionandthecharacteristicsfinite-elementsolutionhavethesameorderofaccuracy.Thenumericalexampleconfirmsthatthetwo-gridmethodismoreefficientthanthatofcharacteristicsfinite-elementmethod.

简介：Thereliabilityandaccuracyofnumericalresultsofmicroparticlefluidizationinaconicalbed,affectedsimultaneouslybymeshrefinement,thegridconfigurationandthewallboundarycondition(BC),areanalyzed.Specifically,pressuregradientsandvelocityprofilesoftitaniapowderarestudiedforaconicalbed.TheGidaspowdragcorrelationanddifferentwallBCsareconsideredusingaEulerian-Euleriantwo-fluidmodel.Predictionsofthepressurefluctuation,powerspectraofthecorrespondingpressurefluctuations,bedpressuredrop,minimumfluidizationvelocity,axialsolidvelocity,bedexpansionratio,andparticlesizedistributionarecomparedwithexperimentaldata.Meshsensitivityanalysisusinghexahedralandtetrahedralcellswithauniformmeshandnear-wallmeshrefinemenrisconductedtoinvestigatetheeffectsofmeshconfigurationsinestimatingparticleflowpatterns.Simulationsshowthatsignificantsavingsintermsofcomputationaltimearerealizedbychoosingauniformmeshwhilethehexahedralstructure,thenear-wallmeshrefinement,andthefree-slipBCgivetheclosestfittotheexperimentaldata.