[saeed jamshidi]

Hi,
I have simulated flow over cylinder in Re=200 in openfoam, and I have used snappyHexMesh, but it looks there are sharp variations in velocity field in the regions that mesh switches from one level to another.
I have attached my mesh and velocity contour for your consideration.
Thanks in advance.

[Yann]

Hello Saeed,

In paraView, try visualizing cell values rather than point values, to see if there is really an issue with the simulation. (see screenshot)

Yann

[saeed jamshidi]

Dear Yann, thank you for your response.
As you can see nothing has changed by visualizing cell values!

[Yann]

OK then maybe you can have a look at your numerical setup in fvSolution and fvSchemes files.

[saeed jamshidi]

Everything looks good!

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v2112                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default         Euler;
}

gradSchemes
{
    default         Gauss linear;
}

divSchemes
{
    default         Gauss linear;

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

laplacianSchemes
{
    default         Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;
}

fluxRequired
{
    default         no;
    p               ;
}


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

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v2112                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    p
    {
        solver           GAMG;
        smoother         DICGaussSeidel;
        tolerance        1e-6;
        relTol           0.01;
    }

    pFinal
    {
        $p;
        relTol          0;
    }

    U
    {
        solver          smoothSolver;
        smoother        symGaussSeidel;
        tolerance       1e-05;
        relTol          0.1;
    }

    UFinal
    {
        $U;
        relTol          0;
    }
}

PIMPLE
{
    nNonOrthogonalCorrectors 0;
    nCorrectors         2;
}


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

[saeed jamshidi]

Hi,
I'm still looking for your opinion about the mentioned problem.
thank you.

[Yann]

Hello Saeed,

Since the issues are located around the cell refinement transitions, I would tend to think you get this effect due to your numerical schemes setup.
Your current setup is based on a tutorial using structured mesh (made with blockMesh) while you have now an unstructured mesh.

I don't have a full setup to advise at the moment, but you can have a look to the tutorials and try other setup to see if it solves your issue.

Let us know if you still get the same issue or if it helps changing schemes.

Yann

[saeed jamshidi]

Dear Yann, thank you for your response.
Yes, it is obvious that the problem is because of snappyHexMesh feature. when i tried blockMesh i didn't see such problem.
Do you mean I should use simplefoam or pisoFoam tutorials?

[Yann]

I don't remember which solver you use, but you can check numerical schemes from the same solver you are using or other solvers too, if you pay attention to the differences between solvers.

For instance on divSchemes, we usually see common setup for div(phi,U) like Gauss upwind (1st Order) or Gauss linearUpwind (2nd order).
There are some resources in the documentation. For instance on the divScheme example: https://doc.openfoam.com/2306/tools/...ence/example/#

More generally: https://doc.openfoam.com/2306/quicks...discretisation
This should lead you to plenty of examples for each operator.

OpenFOAM offers tons of options for numerical setup, so playing around with it can be really time consuming, and this is why I was recommending to check some tutorials to have some examples to base your tests on.

Yann