CFD Online Discussion Forums - turbDyMFoam and Convergence

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turbDyMFoam and Convergence

Hello,

I have used icoDyMFoam to run a turbomachinery case (I was learning to use OpenFOAM, mesh, etc.), and obviously it did not converge.

So I have been trying to implement turbDyMFoam. I have downloaded the files found here: http://openfoamwiki.net/index.php/Si...vaned_diffuser

And transplanted the controlDict, RASProperties, transportProperties, fvsolution, and fvscheme files to my (originally icoDyMFoam) case. I also put boundary conditions on the inlet (freestream) flow (I am doing an external flow with a rotating part) for k and epsilon (zerogradient for everywhere else).

The simulation runs at least, but soon diverges (floating point exception, huge velocity magnitudes).

Can anybody give me a guide to the parameters I can adjust to get convergence?

Thanks in advance.

I get these figures:

Code:

Largest slave weighting factor correction : 1.0817671 average: 1.0000028

  Largest master weighting factor correction: 1 average: 1

When I usually see much much smaller numbers on the forums. What do these figures imply?

It is actually running, and I am only getting floating point exceptions, so I guess that means only the initial conditions are bad. I have tried:

http://www.cfd-online.com/Forums/ope...implefoam.html

http://www.cfd-online.com/Forums/ope...ps-k-re-u.html

None fail to diverge.

Hey guys,

Posting working cases of turbulent external flow using turbdymfoam would be highly appreciated.

Hi lordvon,
I'm trying turbDyMFoam with ggi on wind turbine analysis and it's working well.
I use RAS kOmegaSST turbulence model.

Have you good mesh (especially in nonOrthoFaces check)?
Are your turbulent parameters internalField values correct?

Regards

Hello Andrea, thanks for your reply.

I ran 'checkMesh' and it said that one mesh check failed. I could not discern what exactly this was from the terminal outputs. 'Non-orthogonality check OK.' ; is this what you were talking about? I posted the entirety of the terminal message below.

I have also posted below my initial condition files for k and epsilon. I calculated them using the common formulas. The boundary types in those files are not the only ones I have tested.

Could I take a look at your fvsolution, fvscheme, and /0/ files for k, epsilon, and omega?

Have you tried using RNGkepsilon?

/0/k:

Code:

dimensions      [0 2 -2 0 0 0 0];



internalField   uniform 0.17;



boundaryField

{

    left

    { type                zeroGradient;

//type turbulentIntensityKineticEnergyInlet; 

//intensity 0.05; 

//value 1; 

} 

    top

    { type            zeroGradient; }

    right

    { type            zeroGradient; }

    bottom

    { type            zeroGradient; }

    outsideSlider

    { type            ggi; }

    casing

    { type            zeroGradient; }

    defaultFaces

    { type            empty; }

    insideSlider

    { type            ggi; }

    shaft

    { type            zeroGradient; }

    blades

    { type            zeroGradient; }

}

/0/epsilon:

Code:

dimensions      [0 2 -3 0 0 0 0];



internalField   uniform .67;



boundaryField

{

    left

    { type                zeroGradient;

//type turbulentMixingLengthDissipationRateInlet; 

//mixingLength 0.1; 

//value uniform 200; 

} 

    top

    { type            zeroGradient; }

    right

    { type            zeroGradient; }

    bottom

    { type            zeroGradient; }

    outsideSlider

    { type            ggi; }

    casing

    { type            zeroGradient; }

    defaultFaces

    { type            empty; }

    insideSlider

    { type            ggi; }

    shaft

    { type            zeroGradient; }

    blades

    { type            zeroGradient; }

}

Terminal message for checkMesh:

Code:

Create time



--> FOAM Warning : 

    From function dlLibraryTable::open(const fileName& functionLibName)

    in file db/dlLibraryTable/dlLibraryTable.C at line 86

    could not load libOpenFoamTurbo.so: cannot open shared object file: No such file or directory

Create polyMesh for time = constant



Time = constant



Mesh stats

    points:           72864

    internal points:  0

    faces:            248063

    internal faces:   104627

    cells:            70538

    boundary patches: 10

    point zones:      0

    face zones:       2

    cell zones:       2



Number of cells of each type: 

    hexahedra:     0

    prisms:        70538

    wedges:        0

    pyramids:      0

    tet wedges:    0

    tetrahedra:    0

    polyhedra:     0



Checking topology...

    Boundary definition OK.

    Point usage OK.

    Upper triangular ordering OK.

    Face vertices OK.

   *Number of regions: 2

    The mesh has multiple regions which are not connected by any face.

  <<Writing region information to "constant/cellToRegion"



Checking patch topology for multiply connected surfaces ...

    Patch               Faces    Points   Surface topology                  

    left                37       76       ok (non-closed singly connected)  

    top                 56       114      ok (non-closed singly connected)  

    right               37       76       ok (non-closed singly connected)  

    bottom              56       114      ok (non-closed singly connected)  

    outsideSlider       456      912      ok (non-closed singly connected)  

    casing              670      1340     ok (non-closed singly connected)  

    defaultFaces        141076   72864    ok (non-closed singly connected)  

    insideSlider        456      912      ok (non-closed singly connected)  

    shaft               16       32       ok (non-closed singly connected)  

    blades              576      1152     ok (non-closed singly connected)  



Checking geometry...

    This is a 2-D mesh

    Overall domain bounding box (-1.125 -1.125 0) (2.25 1.125 1)

    Mesh (non-empty) directions (1 1 0)

    Mesh (non-empty, non-wedge) dimensions 2

    All edges aligned with or perpendicular to non-empty directions.

    Boundary openness (-1.6291944e-17 -4.3115768e-17 -1.895701e-23) Threshold = 1e-06 OK.

 ***High aspect ratio cells found, Max aspect ratio: 3898.0533, number of cells 37146 Threshold = 1000

  <<Writing 37146 cells with high aspect ratio to set highAspectRatioCells

    Minumum face area = 2.5918065e-07. Maximum face area = 0.084123393.  Face area magnitudes OK.

    Min volume = 2.5918065e-07. Max volume = 0.0027079637.  Total volume = 7.5688711.  Cell volumes OK.

    Mesh non-orthogonality Max: 33.073843 average: 6.9423388 Threshold = 70

    Non-orthogonality check OK.

    Face pyramids OK.

    Max skewness = 0.49352535 OK.



Failed 1 mesh checks.



End

fvSolution tolerance and reltol

Hello everyone,

Running komegaSST, I no longer get floating point exceptions (at least not yet). However looking at the output through paraFoam, things are still crazy.

I stumbled upon this thread: http://www.cfd-online.com/Forums/ope...timesteps.html , I started to increase tolerance of p's reltol. That decreased the amount of bounding messages, though they still appear.

So I was wondering, can anybody explain how to adjust the fields in fvSolution (preconditioner, tolerance, reltol) to get better convergence and accuracy? Here is a relative section in the OpenFOAM manual: http://www.openfoam.com/docs/user/fvSolution.php

(I am looking into it myself of course, I put this up so that a solution may be worked towards in parallel)
ADDITIONS:
Ok, so I have decided to set all 'reltol's to zero, that way we only have to worry about the 'tolerance'.
Do I need to mess with the preconditioners?
My system files so far:
fvSolution:

Code:

solvers

{

    pcorr PCG

    {

        preconditioner   DIC;

        tolerance        1e-10;

        relTol           0;

    };



    p PCG

    {

        preconditioner   DIC;

        tolerance        1e-10;

        relTol           0;

    };



    pFinal PCG

    {

        preconditioner   DIC;

        tolerance        1e-10;

        relTol           0;

    };



    U PBiCG

    {

        preconditioner   DILU;

        tolerance        1e-10;

        relTol           0;

    };

    k PBiCG

    {

        preconditioner   DILU;

        tolerance        1e-10;

        relTol           0;

    };

    epsilon PBiCG

    {

        preconditioner   DILU;

        tolerance        1e-10;

        relTol           0;

    };

    R PBiCG

    {

        preconditioner   DILU;

        tolerance        1e-10;

        relTol           0;

    };

    omega PBiCG

    {

        preconditioner   DILU;

        tolerance        1e-10;

        relTol           0;

    };



}



PISO

{

    nCorrectors     3;

    nNonOrthogonalCorrectors 1;

    pRefCell        0;

    pRefValue       0;

}

fvSchemes:

Code:

ddtSchemes

{

    default Euler;

}



gradSchemes

{

    default         Gauss linear;

    grad(p)         Gauss linear;

    grad(U)         Gauss linear;

}



divSchemes

{

    default         none;

    div(phi,U)   Gauss upwind;

    div(phi,k)      Gauss upwind;

    div(phi,epsilon) Gauss upwind;

    div(phi,omega) Gauss upwind;

    div(phi,R)      Gauss upwind;

    div(R)          Gauss linear;

    div(phi,nuTilda) Gauss upwind;

    div((nuEff*dev(grad(U).T()))) Gauss linear;

}



laplacianSchemes

{

    default         none;

    laplacian(nuEff,U) Gauss linear corrected;

    laplacian((1|A(U)),p) Gauss linear corrected;

    laplacian(DkEff,k) Gauss linear corrected;

    laplacian(DepsilonEff,epsilon) Gauss linear corrected;

    laplacian(DREff,R) Gauss linear corrected;

    laplacian(DnuTildaEff,nuTilda) Gauss linear corrected;

    laplacian(DomegaEff,omega) Gauss linear corrected;

    laplacian((rho*(1|A(U))),p) Gauss linear corrected;

    laplacian(alphaEff,h) Gauss linear corrected;

    laplacian(rAU,p) Gauss linear corrected;

    laplacian(nu,U) Gauss linear corrected;

    laplacian(1,p)  Gauss linear corrected;



}



interpolationSchemes

{

    default         linear;

    interpolate(U)  linear;

}



snGradSchemes

{

    default         corrected;

}



fluxRequired

{

    default         no;

    p;

}