Lecture9ANSYSFluentOptimizingPreformance

©2011ANSYS,Inc.January10,20201Release14.0Lecture10ANSYSFluentOptimizingPerformancesIntroductiontoANSYDCFD©2011ANSYS,Inc.January10,20202Release14.0Preface•Fluent14的adjointsolver.•风险大,但值得一试.•大量的案例无从着手,无法获得结果.•满足部分工程要求.•已经开始,期待精彩未来.©2011ANSYS,Inc.January10,20203Release14.0KeyIdeas-FundamentalsAdjointsolver是干什么的?•Adjointsolver可提供流体系统很难获得的特定信息.•Adjointsolver可计算关系统输入相关的工程派生量.•Forexample汽车形状相关的阻力.流道形状相关的压力降.©2011ANSYS,Inc.January10,20204Release14.0KeyIdeas-FundamentalsFLOWSOLVERInputs•Boundarymesh•Interiormesh•Materialproperties•Boundarycondition1•Flowangle•Inletvelocity•…•…Outputs•Fielddata•Contourplots•Vectorplots•xy-plots•Scalarvalues•Lift•Drag•Totalpressuredrop常规求解器的‘系统’视角改变输入信息,如何影响关键的输出信息?©2011ANSYS,Inc.January10,20205Release14.0KeyIdeas-Fundamentals流体求解信息q,输入信息c.);(cqJ输出0);(cqR求解NS残差方程0ccRqqR对残差方程线性化处理ChangetheinputscbycccJqqJJ输出改变引入因子0~~ccRqqqRqTTq~qJqqRT~Adjointequations变形ccRqcJJT~ChangeininputsChangeinoutput©2011ANSYS,Inc.January10,20206Release14.0•求解：–求解控制–Courantnumber,under-relaxation.–Residuals&iterations.–类似于常规流场计算.KeyIdeas–AdjointEquations©2011ANSYS,Inc.January10,20207Release14.0KeyIdeas-WorkflowWorkflow•Solvetheflowequationsandpost-processtheresultsasusual.•Pickanobservationthatisofengineeringinterest.Lift,drag,totalpressuredrop?•SetupandsolvetheadjointproblemforthisobservationDefinesolutionadvancementcontrolsSetconvergencecriteriaInitializeIteratetoconvergence•Post-processtheadjointsolutiontogetShapesensitivitySensitivitytoboundaryconditionsettingsContour&vectorplots•ModifythemeshusingameshdeformationapproachMeshmorphing©2011ANSYS,Inc.January10,20208Release14.0KeyIdeas–ShapeSensitivityShapesensitivity:网格(边界)网格节点位置的敏感度.meshnnxwDrag.)(Shapesensitivitycoefficients:VectorfielddefinedonmeshnodesNodedisplacement形状敏感度的可视化•确定敏感度高低位置的确定.•改变这些位置的网格节点位置,对感兴趣的量会有较大的影响.•只针对感兴趣的量及当前流态.DragsensitivityforNACA0012©2011ANSYS,Inc.January10,20209Release14.0KeyIdeas–GradientAlgorithm&Optimization怎样改变节点位移场?•最急剧的下降(Steepestdescent)•位移正比于网格敏感度•在作网格节点移动之前,提供一阶精度的影响评估.meshnnwwDrag.)(FirstorderestimateofthechangeScalingfactorforthedeformation(userchooses)ChosennodedisplacementsnnwxmeshnnxwDrag.)(©2011ANSYS,Inc.January10,202010Release14.0KeyIdeas–MeshMorphingFlow完成设计循环-MeshMorphing•升力(lisf)对面形状的铭感度.•采用Bernstein多项式变形格式.•Adjoint处理变形问题.•面形状的敏感度控制点的敏感度.•这个方法的两个好处:对面敏感度场的smooths操作.对interior变形网格的smooths操作.•选择对部分几何进行修改.©2011ANSYS,Inc.January10,202011Release14.0KeyIdeas–MeshMorphingActualchangeDP=-213.8Totalimprovementof8%网格运动的约束:•控制内的某些面可能不需要运动,需要将其约束住.•只需调整为对控制点敏感度场进行分析,由此对壁面wall带来的变形可以忽略.©2011ANSYS,Inc.January10,202012Release14.0KeyIdeas–MeshAdaptationSolution-basedmeshadaptation•若流场中adjointsolution变量对离散误差有较强影响.•可对adjointsolution变量大的地方进行网格加密AdjointsolutionDragsensitivityBaselineMeshAdaptedMeshAdaptedMeshDetail©2011ANSYS,Inc.January10,202013Release14.0KeyIdeasWhathavewelearnedsofar?•Adjoint求解器可计算所有系统输入相关的工程派生量.•Adjoint方程是一个线性系统.•求解一个adjoint问题并不繁琐–类似于一般的流场计算.•Adjoint求解可为系统级优化提供参考.•Adjoint求解可评估变化对工程性能的影响,而这种评估是在实际变化之前就完成.•Shapesensitivitydata与meshmorphing一起参与对网格的变形与光顺.•Adjointsolution可作为gradient-basedoptimizationalgorithm的一部分.•Adjointsolution可用于指导网格的adaptation.©2011ANSYS,Inc.January10,202014Release14.0Usage©2011ANSYS,Inc.January10,202015Release14.0TheadjointsolverisabetaaddonfeaturetobereleasedwithallFluent14packages.Documentationwillbeavailableonlineviatheuserservicescenter.•Theory•Usage•Tutorial•CasestudyFunctionalityisactivatedby1.Enablingbetafeatures.2.LoadingtheadjointsolveraddonmoduleAnewmenuitemisaddedatthetoplevel.TUIentriesunderadjointUsage-Overview/adjointcontrolsmorphing/reporting/monitors/observable/run/©2011ANSYS,Inc.January10,202016Release14.0GUI•FollowascloseaspossiblesamedesignlayoutasFluentsolver–Specifyobservable–Adjointsolutionadvancementcontrols–Residualmonitors–Initializationanditeration–Post-processing:contours,vectors.–Resultsreporting–Mesh-morphingwithpre-calculationofexpectedchangeinobservable.Usage-Overview©2011ANSYS,Inc.January10,202017Release14.0Usage-OverviewANSYS-FluentflowsolverhasverybroadscopeAdjointisconfiguredtocomputesolutionsbasedonsomeassumptions•Steady,incompressible,laminarflow.•Steady,incompressible,turbulentflowwithstandardwallfunctions.•First-orderdiscretizationinspace.•Frozenturbulence.TheprimaryflowsolutiondoesNOTneedtoberunwiththeserestrictions•Strongevidencethattheseassumptionsdonotunderminetheutilityoftheadjointsolutiondataforengineeringpurposes.Fullyparallelized.Gradientalgorithmforshapemodification•Meshmorphingusingcontrolpoints.Adjoint-basedsolutionadaption©2011ANSYS,Inc.January10,202018Release14.0Usage-OverviewModellimitations•Noporousmedia•NoMRF•Nocompressibility•Noheattransfer•…Twotypesofmodeling-relatedmessagesmaybeprintedintheconsole•Providesdetailsofthedifferencesbetweenhowtheadjointsolverimplementationistreatingtheproblemincomparisontotheconventionalflowsolver.•Warning–Differenceisnotfatal.–Adjointsolvercanexecute.–Maydetractfromqualityofadjointresults.•Error–Modelsusedintheco