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1、Fluent关于壁面设置中的Roughness Height与Roughness ConstantCsKsSettingtheRoughnessParametersTheroughnessparametersareinthe Momentum tabofthe WallDialogBox (see Figure 6.34: TheWallDialogBoxforMarangoniStress),whichisopenedfromthe BoundaryConditionsTaskPage (asdescribedin SettingCellZoneandBoundaryCond
2、itions).Tomodelthewallroughnesseffects,youmustspecifytworoughnessparameters:the RoughnessHeight, ,andthe RoughnessConstant, .Thedefaultroughnessheight( )iszero,whichcorrespondstosmoothwalls.Fortheroughnesstotakeeffect,youmustspecifyanon-zerovaluefor .Forauniformsand-grainroughness,theheig
3、htofthesand-graincansimplybetakenfor .Foranon-uniformsand-grain,however,themeandiameter( )wouldbeamoremeaningfulroughnessheight.Forothertypesofroughness,an“equivalent”sand-grainroughnessheightcouldbeusedfor .Theaboveapproachesareonlyrelevantiftheheightisconsideredconstantpersurface.However
4、,iftheroughnessconstantorroughnessheightisnotconstant,thenyoucanspecifyaprofile(see Profiles).Similarly,user-definedfunctionsmaybeusedtodefineawallroughnessheightthatisnotconstant.Fordetailsontheformatofuser-definedfunctions,refertothe UDFManual.Choosingaproperroughnessconstant( )isdictatedm
5、ainlybythetypeofthegivenroughness.Thedefaultroughnessconstant( )wasdeterminedsothat,whenusedwith - turbulencemodels,itreproducesNikuradse’sresistancedataforpipesroughenedwithtightly-packed,uniformsand-grainroughness.Youmayneedtoadjusttheroughnessconstantwhentheroughnessyouwanttomodeldepart
6、smuchfromuniformsand-grain.Forinstance,thereissomeexperimentalevidencethat,fornon-uniformsand-grains,ribs,andwire-meshroughness,ahighervalue( )ismoreappropriate.Unfortunately,aclearguidelineforchoosing forarbitrarytypesofroughnessisnotavailable.Note: Theroughwallformulationusingtheshiftint
7、roducedin Equation 6–93 eliminatesallrestrictionswithrespecttomeshresolutionnearthewallandcanthereforeberunonarbitraryfinemeshes.两个参数的含义是:roughnessheight粗糙度厚度Ks,也就是通常说的粗糙度,如果Ks=0，则认为是光滑的。如要考虑粗糙度，对于均匀砂粒状表面，可简单任务Ks为砂粒高度；对不均匀表面，可用砂粒平均直径。空气动力学概念粗糙度即粗糙高
