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    jinjolee

    @jinjolee

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    jinjolee 发布的最新帖子

    • RE: [菜鳥求救] K-omega SST 头几秒就崩溃了

      @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...:chigua:

      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:mihu: :mihu:

      发布在 OpenFOAM
      J
      jinjolee
    • RE: [菜鳥求救] K-omega SST 头几秒就崩溃了

      @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。:wanan:
      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?

      发布在 OpenFOAM
      J
      jinjolee
    • RE: [菜鳥求救] K-omega SST 头几秒就崩溃了

      @Foamer24 在 [菜鳥求救] K-omega SST 头几秒就崩溃了 中说:

      我指的是fluent选择k omega初始化的时候,就可以看到fluent里面的初始值。可以拿来和你现在的初始值对照下。

      我上面的留言格式弄错了, 我再发一次。

      能请教一下怎么查看吗? 我没怎用ANSYS,不太清楚。
      是不是要先汇入模型,生成网格,然后进了setup才可以看到omega的初始值?

      发布在 OpenFOAM
      J
      jinjolee
    • RE: [菜鳥求救] K-omega SST 头几秒就崩溃了

      @Foamer24 在 [菜鳥求救] K-omega SST 头几秒就崩溃了 中说:

      我指的是fluent选择k omega初始化的时候,就可以看到fluent里面的初始值。可以拿来和你现在的初始值对照下。
      能请教一下怎么查看吗? 我没怎用ANSYS,不太清楚。
      是不是要先汇入模型,生成网格,然后进了setup才可以看到omega的初始值?

      发布在 OpenFOAM
      J
      jinjolee
    • RE: [菜鳥求救] K-omega SST 头几秒就崩溃了

      @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
      ~~~~~~~~~~
      @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。
      ~~~~~~~~~~
      @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 :duang:

      可是我怎么算怎么试,结果还是发散。:zoule:
      有方法可以分辨出k和omega的初始值是太大或太小吗?

      发布在 OpenFOAM
      J
      jinjolee
    • RE: [菜鳥求救] K-omega SST 头几秒就崩溃了

      @东岳 在 [菜鳥求救] K-omega SST 头几秒就崩溃了 中说:

      CFD发散并没有一阵见血的解决办法。目前很难判断哦,但我觉得你一定会搞定的 :ok2:

      老师你太高估我了 我只是个新手渣渣 光凭我自己一个始终有点吃力:mihu:
      其实我在怀疑这会不会是k和omega的初始值所造成的问题,毕竟这都是估算的,没有实验根据,而且听说k omega对初始值很敏感。请问老师有没有方法可以验证初始值是否合适?

      发布在 OpenFOAM
      J
      jinjolee
    • RE: [菜鳥求救] K-omega SST 头几秒就崩溃了

      @东岳 在 [菜鳥求救] K-omega SST 头几秒就崩溃了 中说:

      排版满分。
      你用自带的摩托车网格试试?
      你这个只能看出是发散了原因有很多不好判断

      谢谢老师的指教 我降低了网格refinement level, 也尝试了把松弛因子调低,结果还是发散。
      有其么其他的建议吗?:papa:

      发布在 OpenFOAM
      J
      jinjolee
    • [菜鳥求救] K-omega SST 头几秒就崩溃了

      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);
      }
      
      发布在 OpenFOAM
      J
      jinjolee
    • 应该如何计算外部流场的k和epsilon?

      看到站內的一篇文章, 有提及到使用turbulence length scale和turbulence intensity level来计算k和epsilon。可是查看了一下,turbulence length scale和intensity level都需要使用水力直徑来计算。那么对于外部流场来说,应该要如何计算?通常模拟汽车移动的外部流场,在OpenFOAM中,上、左和右壁都设定为slip wall,那水力直徑还应该把它当成内部流场那样以inlet的高和宽来计算吗?
      小弟的流体知识浅薄,还请多多指教:shangxue:

      发布在 OpenFOAM
      J
      jinjolee
    • RE: 如何在simpleFoam kEpsilon中加入重力?

      @东岳 其实我是想看一下加了重力会不会对CdA和Cp做成影响 如果没有多大影响的话 就可以不考虑重力了

      发布在 OpenFOAM
      J
      jinjolee