[菜鳥求救] K-omega SST 头几秒就崩溃了
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我在模𣝅单车行驶的外部流场，主要是想求CdA。湍流模型用了k omega SST，求解器则是用了simpleFoam。我借用了motorBike的范例，稍为修改了一下。我设了初始速度为15m/s，0Pa。以下是log.simpleFoam里的头几个iteration:
Create time Create mesh for time = 0 [AdminPC:02105] 5 more processes have sent help message help-btl-vader.txt / cma-permission-denied [AdminPC:02105] Set MCA parameter "orte_base_help_aggregate" to 0 to see all help / error messages SIMPLE: Convergence criteria found U: tolerance 0.0001 p: tolerance 0.0001 "(k|omega)": tolerance 0.0001 Reading field p Reading field U Reading/calculating face flux field phi Selecting incompressible transport model Newtonian Selecting turbulence model type RAS Selecting RAS turbulence model kOmegaSST Selecting patchDistMethod meshWave RAS { RASModel kOmegaSST; turbulence on; printCoeffs on; alphaK1 0.85; alphaK2 1; alphaOmega1 0.5; alphaOmega2 0.856; gamma1 0.555556; gamma2 0.44; beta1 0.075; beta2 0.0828; betaStar 0.09; a1 0.31; b1 1; c1 10; F3 false; } No MRF models present No finite volume options present Starting time loop streamLine streamLines: automatic track length specified through number of sub cycles : 5 Reading surface description: yNormal forces forceCoeffs1: Not including porosity effects forceCoeffs forceCoeffs1: Not including porosity effects Time = 1 smoothSolver: Solving for Ux, Initial residual = 0.176082, Final residual = 0.0175161, No Iterations 8 smoothSolver: Solving for Uy, Initial residual = 0.0854752, Final residual = 0.0078422, No Iterations 6 smoothSolver: Solving for Uz, Initial residual = 0.0535574, Final residual = 0.00446781, No Iterations 9 GAMG: Solving for p, Initial residual = 1, Final residual = 0.00968802, No Iterations 15 time step continuity errors : sum local = 9.19838e-08, global = 1.35003e-09, cumulative = 1.35003e-09 smoothSolver: Solving for omega, Initial residual = 0.999998, Final residual = 2.29698e-05, No Iterations 1 smoothSolver: Solving for k, Initial residual = 1, Final residual = 6.96747e-05, No Iterations 1 ExecutionTime = 252.73 s ClockTime = 563 s forceCoeffs forceCoeffs1 write: Cm = 0.404453 Cd = 0.754425 Cl = -0.0101646 Cl(f) = 0.399371 Cl(r) = -0.409535 Time = 2 smoothSolver: Solving for Ux, Initial residual = 0.114146, Final residual = 0.00945059, No Iterations 8 smoothSolver: Solving for Uy, Initial residual = 0.03572, Final residual = 0.0033767, No Iterations 7 smoothSolver: Solving for Uz, Initial residual = 0.268761, Final residual = 0.023381, No Iterations 8 GAMG: Solving for p, Initial residual = 0.00423399, Final residual = 3.88164e-05, No Iterations 14 time step continuity errors : sum local = 7.09901e-08, global = 1.05225e-09, cumulative = 2.40228e-09 smoothSolver: Solving for omega, Initial residual = 0.786768, Final residual = 6.02541e-05, No Iterations 1 smoothSolver: Solving for k, Initial residual = 0.347618, Final residual = 8.09935e-05, No Iterations 1 ExecutionTime = 358.52 s ClockTime = 941 s forceCoeffs forceCoeffs1 write: Cm = 0.372383 Cd = 0.710432 Cl = -0.0032843 Cl(f) = 0.370741 Cl(r) = -0.374025 Time = 3 smoothSolver: Solving for Ux, Initial residual = 0.134328, Final residual = 0.0118087, No Iterations 8 smoothSolver: Solving for Uy, Initial residual = 0.116996, Final residual = 0.0105707, No Iterations 7 smoothSolver: Solving for Uz, Initial residual = 0.0580452, Final residual = 0.00576293, No Iterations 7 GAMG: Solving for p, Initial residual = 0.00317963, Final residual = 3.03476e-05, No Iterations 18 time step continuity errors : sum local = 7.20084e-08, global = 7.35963e-10, cumulative = 3.13824e-09 smoothSolver: Solving for omega, Initial residual = 0.373588, Final residual = 9.57613e-05, No Iterations 1 smoothSolver: Solving for k, Initial residual = 0.103448, Final residual = 8.1809e-05, No Iterations 1 ExecutionTime = 509.1 s ClockTime = 1274 s forceCoeffs forceCoeffs1 write: Cm = 0.28686 Cd = 0.550375 Cl = 0.0178247 Cl(f) = 0.295772 Cl(r) = -0.277947 Time = 4 smoothSolver: Solving for Ux, Initial residual = 0.581453, Final residual = 0.0506933, No Iterations 7 smoothSolver: Solving for Uy, Initial residual = 0.438063, Final residual = 0.0375534, No Iterations 14 smoothSolver: Solving for Uz, Initial residual = 0.28364, Final residual = 0.0228554, No Iterations 19 GAMG: Solving for p, Initial residual = 0.100663, Final residual = 0.000964993, No Iterations 24 time step continuity errors : sum local = 2.71584e-06, global = -6.86095e-08, cumulative = -6.54713e-08 smoothSolver: Solving for omega, Initial residual = 0.156237, Final residual = 0.000151387, No Iterations 1 smoothSolver: Solving for k, Initial residual = 0.0248487, Final residual = 9.03384e-05, No Iterations 1 ExecutionTime = 625.86 s ClockTime = 1558 s forceCoeffs forceCoeffs1 write: Cm = -2.36372 Cd = 5.23947 Cl = -45.4406 Cl(f) = -25.084 Cl(r) = -20.3566 Time = 5 smoothSolver: Solving for Ux, Initial residual = 0.748694, Final residual = 0.0654467, No Iterations 6 smoothSolver: Solving for Uy, Initial residual = 0.707975, Final residual = 0.0671149, No Iterations 10 smoothSolver: Solving for Uz, Initial residual = 0.645301, Final residual = 0.0580618, No Iterations 11 GAMG: Solving for p, Initial residual = 0.331992, Final residual = 0.00325251, No Iterations 29 time step continuity errors : sum local = 4.57856e-05, global = 1.35323e-06, cumulative = 1.28776e-06 smoothSolver: Solving for omega, Initial residual = 0.0619606, Final residual = 0.000791318, No Iterations 1 smoothSolver: Solving for k, Initial residual = 0.00576973, Final residual = 0.000313824, No Iterations 2 ExecutionTime = 753.75 s ClockTime = 1825 s forceCoeffs forceCoeffs1 write: Cm = 48393.6 Cd = 355643 Cl = -193536 Cl(f) = -48374.2 Cl(r) = -145161 Time = 6 smoothSolver: Solving for Ux, Initial residual = 0.77583, Final residual = 0.0469625, No Iterations 11 smoothSolver: Solving for Uy, Initial residual = 0.647136, Final residual = 0.0587523, No Iterations 9 smoothSolver: Solving for Uz, Initial residual = 0.801675, Final residual = 0.0450629, No Iterations 11 GAMG: Solving for p, Initial residual = 2.42318e-05, Final residual = 2.34325e-07, No Iterations 43 time step continuity errors : sum local = 0.000116095, global = 5.64454e-06, cumulative = 6.9323e-06 smoothSolver: Solving for omega, Initial residual = 0.0295412, Final residual = 0.00216916, No Iterations 2 smoothSolver: Solving for k, Initial residual = 0.00243104, Final residual = 0.000230323, No Iterations 3 ExecutionTime = 908.36 s ClockTime = 2133 s forceCoeffs forceCoeffs1 write: Cm = -735398 Cd = -1.66962e+06 Cl = -1.74826e+07 Cl(f) = -9.47672e+06 Cl(r) = -8.00593e+06 Time = 7 smoothSolver: Solving for Ux, Initial residual = 0.577761, Final residual = 0.0517967, No Iterations 47 smoothSolver: Solving for Uy, Initial residual = 0.570563, Final residual = 0.0531017, No Iterations 47 smoothSolver: Solving for Uz, Initial residual = 0.546372, Final residual = 0.0538754, No Iterations 36 GAMG: Solving for p, Initial residual = 0.0134, Final residual = 0.0431707, No Iterations 1000 time step continuity errors : sum local = 500.302, global = -256.052, cumulative = -256.052 smoothSolver: Solving for omega, Initial residual = 0.726855, Final residual = 0.0688681, No Iterations 4 smoothSolver: Solving for k, Initial residual = 0.053017, Final residual = 0.00485332, No Iterations 4 ExecutionTime = 2723 s ClockTime = 4119 s forceCoeffs forceCoeffs1 write: Cm = 1.42517e+06 Cd = 7.85747e+06 Cl = -2.46218e+07 Cl(f) = -1.08857e+07 Cl(r) = -1.37361e+07 Time = 8 smoothSolver: Solving for Ux, Initial residual = 0.612081, Final residual = 0.0499664, No Iterations 29 smoothSolver: Solving for Uy, Initial residual = 0.562296, Final residual = 0.0483684, No Iterations 28 smoothSolver: Solving for Uz, Initial residual = 0.628358, Final residual = 0.0614706, No Iterations 14 GAMG: Solving for p, Initial residual = 0.999964, Final residual = 0.0500564, No Iterations 1000 time step continuity errors : sum local = 1.61271e+08, global = -40286.8, cumulative = -40542.9 smoothSolver: Solving for omega, Initial residual = 0.00412419, Final residual = 0.000290188, No Iterations 4 smoothSolver: Solving for k, Initial residual = 0.00274375, Final residual = 0.000233623, No Iterations 5 ExecutionTime = 4529.61 s ClockTime = 6088 s forceCoeffs forceCoeffs1 write: Cm = -6.60893e+13 Cd = -5.13466e+14 Cl = 1.211e+14 Cl(f) = -5.53934e+12 Cl(r) = 1.26639e+14 Time = 9 smoothSolver: Solving for Ux, Initial residual = 0.804576, Final residual = 13.5575, No Iterations 1000 smoothSolver: Solving for Uy, Initial residual = 0.785135, Final residual = 82.7634, No Iterations 1000 smoothSolver: Solving for Uz, Initial residual = 0.874744, Final residual = 9.53614, No Iterations 1000 ------------------------------------------------------- Primary job terminated normally, but 1 process returned a non-zero exit code.. Per user-direction, the job has been aborted. ------------------------------------------------------- -------------------------------------------------------------------------- mpirun detected that one or more processes exited with non-zero status, thus causing the job to be terminated. The first process to do so was: Process name: [[12118,1],0] Exit code: 145 --------------------------------------------------------------------------可见在第四秒就崩溃了。Boundary Condition我都是参考motorbike的, 只改了velocity, k和omega:
- flowVelocity (0 0 15);
- pressure 0;
- turbulentKE 0.00135;
- turbulentOmega 900;
k和omega的值是我参考了其他文章,用了turbulence intensity level = 0.2%, 和eddy viscousity ratio = 0.1，从而算出來的。
以下是snappyHexMeshDict, fvScheme 和 fvSolution，求求大佬指点一下问题出在哪,谢谢
snappyHexMesh:
castellatedMesh true; snap true; addLayers true; { figure { type triSurfaceMesh; file "figure.stl"; } refinementBox { type searchableBox; min ( -750 0 -1000); max ( 1830 2685 2640); } }; castellatedMeshControls { maxLocalCells 1000000; maxGlobalCells 30000000; minRefinementCells 15; maxLoadUnbalance 0.15; nCellsBetweenLevels 3; features ( { file "figure.eMesh"; level 7; } ); refinementSurfaces { figure { level (7 7); patchInfo { type wall; inGroups (figureGroup); } } } resolveFeatureAngle 20; refinementRegions { refinementBox { mode inside; levels ((1E15 4)); } figure { mode distance; levels ( (2 8) (10 6) ); } } locationInMesh (402.1 1802 1002.7) ; allowFreeStandingZoneFaces true; } snapControls { nSmoothPatch 5; tolerance 2.25; nSolveIter 30; nRelaxIter 5; nFeatureSnapIter 10; implicitFeatureSnap false; explicitFeatureSnap true; multiRegionFeatureSnap false; } addLayersControls { relativeSizes true; layers { "(lowerWall|figure).*" { nSurfaceLayers 10; } } expansionRatio 1.2; thickness 0.8; minThickness 0.0001; nGrow 0; featureAngle 180; slipFeatureAngle 30; nRelaxIter 5; nSmoothSurfaceNormals 1; nSmoothNormals 3; nSmoothThickness 10; maxFaceThicknessRatio 0.6; maxThicknessToMedialRatio 0.3; minMedianAxisAngle 90; nBufferCellsNoExtrude 0; nLayerIter 15; } meshQualityControls { #include "meshQualityDict" } writeFlags ( scalarLevels layerSets layerFields ); mergeTolerance 1e-6;fvSchemes:
ddtSchemes { default steadyState; } gradSchemes { default Gauss linear; grad(U) cellLimited Gauss linear 1; } divSchemes { default none; div(phi,U) bounded Gauss linearUpwindV grad(U); div(phi,k) bounded Gauss upwind; div(phi,omega) bounded Gauss upwind; div((nuEff*dev2(T(grad(U))))) Gauss linear; } laplacianSchemes { default Gauss linear corrected; } interpolationSchemes { default linear; } snGradSchemes { default corrected; } wallDist { method meshWave; }fvSolution:
solvers { p { solver GAMG; smoother GaussSeidel; tolerance 1e-7; relTol 0.01; } Phi { $p; } U { solver smoothSolver; smoother GaussSeidel; tolerance 1e-8; relTol 0.1; nSweeps 1; } k { solver smoothSolver; smoother GaussSeidel; tolerance 1e-8; relTol 0.1; nSweeps 1; } omega { solver smoothSolver; smoother GaussSeidel; tolerance 1e-8; relTol 0.1; nSweeps 1; } } SIMPLE { nNonOrthogonalCorrectors 0; consistent yes; residualControl { U 1e-4; p 1e-4; "(k|omega)" 1e-4; } } potentialFlow { nNonOrthogonalCorrectors 10; } relaxationFactors { equations { U 0.9; k 0.7; omega 0.7; } } cache { grad(U); } -
simpleFoam是稳态求解器，你这个问题是不是用瞬态比较好？如果你模拟的流场达不到稳态可能会这样。建议用pimpleFoam试试。
而且，k-omega SST稳定性很好，对初值没有k-omega模型这么敏感吧。 -
@Foamer24 在 [菜鳥求救] K-omega SST 头几秒就崩溃了 中说：
@jinjolee k和omega可以用fluent里面初始化的值做参考
我的模型放进Ansys后貌似有点问题，无法顺利生成enclosure，要把其中一个部件去除才行，而且每次生成boundary later都会报错，无法生成。因此ansys fluent对我来说可能不是最佳方案
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@tidedrinker 在 [菜鳥求救] K-omega SST 头几秒就崩溃了 中说：simpleFoam是稳态求解器，你这个问题是不是用瞬态比较好？如果你模拟的流场达不到稳态可能会这样。建议用pimpleFoam试试。
而且，k-omega SST稳定性很好，对初值没有k-omega模型这么敏感吧。我试过用pimpleFoam，但貌似设置有点问题，发散问题更严重。所以想先用simpleFoam试试看。
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@东岳 在 [菜鳥求救] K-omega SST 头几秒就崩溃了 中说：@jinjolee 在 [菜鳥求救] K-omega SST 头几秒就崩溃了 中说：
听说k omega对初始值很敏感
是的，kOmega模型是这样的。不过Omega可以从epsilon计算出来：$\Omega=\frac{\varepsilon}{0.09 k} $
你这个我感觉完全是边界条件设置的问题，因为不涉及到算法，你会会搞定的
可是我怎么算怎么试，结果还是发散。
有方法可以分辨出k和omega的初始值是太大或太小吗？ -
@dzw05 在 [菜鳥求救] K-omega SST 头几秒就崩溃了 中说：
@jinjolee 你拿个最简单的模型导入fluent就可以了，只是借用一下fluent的初始化k和omega值。其实k和omega的值与速度的关系是有理论公式的，fluent也是用这个理论公式算出来的，看一下fluent的帮助手册。或者看这个网址湍流边界条件
我就是用你给的那个网址里的论坛的工具去算的。只是我摸拟的是外部流场，turbulence length scale比较难预测，只能用eddy viscosity ratio去算，而那论坛里好像也没有相关的资料（例如在什么情况下，eddy viscosity ratio大约是多少之类的）。
至于ansys fluent，可能是我还没弄清楚设置，试了一下还是发散了。看来得再研究一下。
话说在一个普通的室外环境里（零风速），eddy viscosity ratio大约是多少？有参考值吗？ -
@dzw05 在 [菜鳥求救] K-omega SST 头几秒就崩溃了 中说：
@jinjolee eddy viscosity ratio一般设大于1小于10，给个10应该就行。另外，你这个不一定是湍流模型导致的发散，直接用层流先试试，逐个排除原因。
可是奇怪的是我之前用k-epsilon模型来算，当时用了:
turbulentKE=0.17557; turbulentEpsilon=0.05677;这样来算，反而结果有收敛，另外reynold number也得出为1638000，所以我认为基本上得用湍流模型。不过这个CdA比正常的低(我的结果只有0.26左右，而从其他的实验结果得来是0.46左右)。我当时用的是:
flowVelocity=12.5;,而k是用turbulence intensity level = 2.73%。至于这个2.73%和epsilon的值是怎得来的，老实说我忘了...
我之后从不同文献中看到湍流的k和epsilon初始值应该要以模拟的环境在现实中的特征来作基础(例如我在模拟单车在行驶，虽然在CFD中我给了个15m/s的风速，但turbulence intensity level的初始应该不是以这个15m /s的速度来算，而是以真实环境(0风速)来算，所以turbulence intensity level应该很低，大约0.2~0.02%左右)。然而我换了turbulence intensity level=0.2%后，结果就一直发散。
快烦死了
