Ansys12CFX官方教程11B.ppt

Chapter11CFXExpressionLanguage CEL IntroductiontoCFX CEL CFXExpressionLanguageAllowstheusertocreateequations canbefunctionsofsolution systemvariables thatcanbeusedinCFX PreandCFD PostExample CEL Thesyntaxrulesarethesameasthoseforconventionalarithmetic Operatorsarewrittenas addition subtraction multiplication division exponentiation Variablesandexpressionsarecasesensitive example tvs T Expressionsmustbedimensionallyconsistentforadditionandsubtractionoperations example 1 0 mm 0 45 yds isOK YoucannotaddvalueswithinconsistentdimensionsFractionalanddecimalpowersareallowed example a 1 2 1 0 0 5 Unitsofexpressionsarenotdeclared theyaretheresultofunitsintheexpression example a kgm 3 b ms 1 hasunitsof kgm 2s 1 SomeconstantsarealsoavailableinCELforuseinexpressions eConstant 2 7182818gAccelerationduetogravity 9 806 ms 2 piConstant 3 1415927RUniversalGasConstant 8314 5 m 2s 2K 1 CELRules NumericalfunctionsandoperatorsarealsoavailableinCELRight clickwhencreatingexpressionsforacompletelistCustomfunctionswithUserFortrancanalsobecreated FunctionOperand sDimensions x Operand sValuesResult sDimensionssin x AngleAnyDimensionlesscos x AngleAnyDimensionlesstan x AngleAnyDimensionlessasin x Dimensionless 1 x 1Angleacos x Dimensionless 1 x 1Angleatan x DimensionlessAnyAngleexp x DimensionlessAnyDimensionlessloge x Dimensionless01 m 1 0 Inthiscase iftheresultispreciselyequalto1 m theresultis res1 res2 2 step x is0fornegativex 1forpositivexand0 5forx 0 notethattan x isundefinedfornp 2wheren 1 3 5 bothxandymusthavethesamedimensions BuiltInFunctions xDirection1inReferenceCoordinateFrameyDirection2inReferenceCoordinateFramezDirection3inReferenceCoordinateFramerRadialspatiallocation r x 2 y 2 0 5thetaAngle arctan y x tTimeuVelocityinthexcoordinatedirectionvVelocityintheycoordinatedirectionwVelocityinthezcoordinatedirectionp absolute PressurekeTurbulentkineticenergyedTurbulenteddydissipationTTemperaturesstrnrShearstrainratedensityDensityrNoDimNon dimensionalradius rotatingframeonly viscosityDynamicViscosityCpSpecificHeatCapacityatConstantPressurecondThermalConductivityAVnameAdditionalVariablenamemfMassFraction SolvervariablesareavailableforuseinanyexpressionBelowisapartiallistoftheavailablesystemvariables Whencreatingexpressions right clicktoaccessafulllist Dependingonyourphysics somevariableswillnotbevalid e g youneedtosolverheattransfertouseT SolverVariables HowToCreateExpressions Toaddmoreexpressions similarmethodinCFD Post HowToCreateExpressions Right clickintheDefinitionwindowtoaccessVariables Constants Functions LocatorsandexistingExpressions where istheshearstrainrate CreatingavariableviscosityViscosityofashearthickeningfluid SolverVariableandExpressionNamearebothaccessedviatherightmousebutton CELinCFX Pre Example1 Alternatively anexpressioncanbeentereddirectlyintoafield CELinCFX Pre Example1 Usingan if FunctionSetinlettemperatureto300Kforthefirst19iterationsthenraiseitto320Kafter20iterations Solvervariableaccessedwiththerightmousebutton Note Onthe21stiterationinlettemp 310K CELinCFX Pre Example2 Youcanalsodefineyourown1 Dlinear or3 Dcloudofpointsinterpolationfunctions Importdatapointsoraddmanually UserFunctions Example Havingthetimestepchangewithiterationnumberasshownhere Timestepsizeisinseconds Continuedonnextslide UserFunctions Example IterationNumberisdimensionless Example Havingthetimestepchangewithiterationnumberasshownhere UserFunctions Example IntegratedquantitiescanbeusedinexpressionstoevaluatevariablesoversomelocationExamples CalculatetheareaaverageofCponanisosurface areaAve Cp iso1Massflowofparticularfluidthroughalocator oil massFlow slice1AvailableinCFX PreandCFD PostUsageismorestrictinCFX PreE g theargumentsuppliedtothefunctionmustbeavariable notanexpression syntaxmustalwayssupplyanamedlocationusedinthephysicsdefinitionAboundaryconditionname adomainname amonitorpointname etc Toreferencegeneralmeshregionsusethesyntax REGION Phases componentscanbereferencedusing E g Air Nitrogen massFlow outlet IntegratedQuantities IntegratedQuantities Somefunctionsallowanx yorzoperator area x boundarygivestheareaprojectedinthex directionforce z wallgivesthezcomponentoftheforceonthewallSeedocumentationforafulllistThesefunctionsalsoallowanoptionalcoordinateframe force z MyCoord wallgivesthezcomponentoftheforceonthewallusingthecoordinateframe MyCoord Eachfunctionrequireseither0or1argumentsareaAverequires1argument areaAve Temperature WallmassFlowrequires0arguments massFlow InletReturnvalueunitsdependontheargumentunitsareaAve Temperature WallwillreturnavaluewithunitsofTemperature BelowisapartiallistoffunctionsSeedocumentationforacompletelistRight clickingwhencreatinganexpressionwillshowmostfunctions IntegratedQuantities IntegratedQuantities IntegratedQuantities UsefulFunctions Theinside functionreturns1wheninsidethespecifiedlocationand0whenoutsideUsefultolimitthescopeofafunctiontoasubdomainorboundaryThestep functionreturn1whentheargumentispositiveand0whentheargumentisnegativeUsefulasanon offswitchif functioncanalsobeusedasaswitchareaAve andmassFlowAve areusedtoevaluatetheaverageofaquantityonalocationareaAve isanarea w