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lg88 January 26, 2013 10:23

About the non-orthogonal mesh and non-orthogonal corrector
 
2 Attachment(s)
Hello everyone
I used a modified solver to simulate a circular pipe flow.The mesh is non-orthogonal.So I think I need use non-orthogonal corrector in the fvSchemes. But the results is not good as the time developing.It seems that the mesh have great influence to the velocity.I have attached my velocity contours and mesh here.I hope you can help me to analysis the the fvSchemes I used. I think the problem maybe lie in the non-orthogonal corrector,but I don't have enough experience.I set the fvSchemes as following:
Code:

ddtSchemes
{
    default        Euler;
}

gradSchemes
{
      default        cellLimited leastSquares 1;
  // grad(p)        Gauss linear;
}

divSchemes
{
    default        none;
    div(phi,U)      Gauss linearUpwindV cellMDLimited leastSquares 1.0;
    div(phi)      Gauss linear 1;
    div(phiB,Dsig)  Gauss linear 1;
}

laplacianSchemes
{
    default        Gauss linear corrected;
    laplacian(nu,U) Gauss linear corrected;
    laplacian((1|A(U)),p) Gauss linear corrected;

    laplacian(DT,T)    Gauss linear corrected;
}

interpolationSchemes
{
    default        linear;
    interpolate(HbyA) linear;
}

snGradSchemes
{
    default        corrected;
}

fluxRequired
{
    default        no;
    p;
}

Thank you for your advice.
regards!


lg88

wyldckat January 27, 2013 07:15

Hi lg88,

What do you have in "system/fvSolution"? I'm asking this because the number of correctors is defined on that file: http://www.openfoam.org/docs/user/fvSolution.php

Best regards,
Bruno

lg88 January 27, 2013 09:53

Thank you for your reply.I set my fvSolution as following:
Code:

solvers
{
    p
    {
        solver          PCG;
        preconditioner  DIC;
        tolerance        1e-06;
        relTol          0;
    };
    pFinal
    {
        solver          PCG;
        preconditioner  DIC;
        tolerance        1e-06;
        relTol          0;
    };

    ephi
    {
        solver          PCG;
        preconditioner  DIC;
        tolerance      1e-06;
        relTol          0;
    };

    U
    {
        solver          PBiCG;
        preconditioner  DILU;
        tolerance        1e-05;
        relTol          0;
    };
}

PISO
{
    nCorrectors    3;
    nNonOrthogonalCorrectors 3;
    pRefCell        0;
    pRefValue      0;
}

// ************************************************************************* //

I have set the number of correctors from 1 to 3,but the result is almost the same in the end.The velocity at the four corners has odd behavious as the attached picture show.


Best regards!

lg88

wyldckat January 27, 2013 16:15

Hi lg88,

I'm not experienced enough on this, but I suggest that you also provide the following details, so that someone with more experience can help you during this week:
  1. Have you checked the state of the mesh? What does checkMesh give you? And what about a full check, namely:
    Code:

    checkMesh -allGeometry -allTopology
  2. What solver (or based on which solver) are you using?
    • On a side note: have you confirmed that the solver you're using does apply this number?
  3. What's in play? More specifically: the fluid type, speeds that it reaches, the Reynolds number it can reach, and so on...
Best regards,
Bruno

lg88 January 28, 2013 07:51

Hi Bruno
I run the command
Code:

checkMesh
and got the following message:
Code:

Checking geometry...
    This is a 3-D mesh
    Overall domain bounding box (-1 -1 0) (1 1 0.02)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Mesh (non-empty, non-wedge) dimensions 3
    Boundary openness (4.2856998285e-20 5.9259059357e-20 -2.7446997359e-19) Threshold = 1e-06 OK.
    Max cell openness = 3.9590866047e-16 OK.
    Max aspect ratio = 159.52539546 OK.
    Minumum face area = 1.5253865084e-06. Maximum face area = 0.0014060260459.  Face area magnitudes OK.
    Min volume = 1.061859197e-07. Max volume = 2.8120520918e-05.  Total volume = 0.062779645967.  Cell volumes OK.
    Mesh non-orthogonality Max: 88.365490847 average: 7.2145668686 Threshold = 70
  *Number of severely non-orthogonal faces: 32.
    Non-orthogonality check OK.
  Writing 32 non-orthogonal faces to set nonOrthoFaces
    Face pyramids OK.
    Max skewness = 0.81894169959 OK.

Mesh OK

I think the mesh quality is good.
I modified my solver according icoFoam.
The fluid in my case is not a real material.I set its density to 1,kinematic viscosity 0.001,velocity 1 and Reynolds number 1000.

Then I modified the laplacianSchemes from
Code:

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

    laplacian(DT,T)    Gauss linear corrected;
}

to
Code:

{
    default        Gauss linear limited 0.5//or 0.333;
    laplacian(nu,U) Gauss linear limited 0.5//or 0.333;
    laplacian((1|A(U)),p) Gauss linear limited 0.5//or 0.333;

    laplacian(DT,T)    Gauss linear limited 0.5//or 0.333;
}

But I got worse result.
I have no ideal about it.

Thanks for your advice.

regards!

lg88

lg88 January 29, 2013 03:53

Hello everyone
When I set the laplacianSchemes from:
Code:

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

    laplacian(DT,T)    Gauss linear corrected;
}

to
Code:

{
    default        Gauss linear limited 0.5//or 0.333;
    laplacian(nu,U) Gauss linear limited 0.5//or 0.333;
    laplacian((1|A(U)),p) Gauss linear limited 0.5//or 0.333;

    laplacian(DT,T)    Gauss linear limited 0.5//or 0.333;
}

,the calculation will be divergence with few iterations.The velocity will be very large.I don't have any experience on this.Thank you for your advice.

regards!

lg88

fredo490 March 4, 2013 11:56

In my point of view your skewness looks a bit high (0.8). I had a similar problem that I solved by introducing a skewcorrector. You can look at my scheme here http://www.cfd-online.com/Forums/ope...om-solver.html

startingWithCFD March 5, 2013 04:04

Sorry for the stupid question but I am curious:
If it is a simple, straight pipe, why do you not have a square block in the middle?
Why are its edges curved in this manner?
Maybe changing this may improve your mesh properties and therefore correct your solution.

fredo490 March 5, 2013 04:11

I guess he used a "smoothing" function from his grid generator. Sometimes I get the same kind of restults with Pointwise.


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