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-   -   Flow around airfoil using WALE LES model, why Cp and Cf are not correct? (https://www.cfd-online.com/Forums/openfoam-solving/224293-flow-around-airfoil-using-wale-les-model-why-cp-cf-not-correct.html)

navidmt February 12, 2020 17:57
Flow around airfoil using WALE LES model, why Cp and Cf are not correct?
 
Hi everyone! I was running a case of flow passing an airfoil at Reynolds 60000 using WALE LES model in OpenFoam and after checking the Pressure and Skin friction coefficients,I noticed that the results are very different that the previous studies, and I don't know what could be the source of problem.
For this reason, I am gonna share all my settings here with you hopefully someone can tell me what was my mistake!
The mesh I was using is very dense around the airfoil that I have y+<1 , so I haven't used any wall function. Also I used
Code:
FoamFile
{
        version 2.0;
        format binary;
        class volVectorField;
        location "";
        object U;
}
/*---------------------------------------------------------------------------*/
/*---------------------------------------------------------------------------*/


dimensions [0 1 -1 0 0 0 0];

internalField uniform (0.970295726 0.2419218955 0.);


boundaryField
{
        in
        {
                type fixedValue;
                value        uniform (0.970295726 0.2419218955 0.);
        }

        out
        {
                type zeroGradient;
        }

        wallup
        {
                type fixedValue;
                value        uniform (0. 0. 0.);
        }

        walldown
        {
                type fixedValue;
                value        uniform (0. 0. 0.);
        }

       
        front
        {
                type cyclic;
        }

        back
        {
                type cyclic;
        }


}
Code:
FoamFile
{
        version 2.0;
        format binary;
        class volScalarField;
        location "";
        object p;
}
/*---------------------------------------------------------------------------*/
/*---------------------------------------------------------------------------*/


dimensions [0 2 -2 0 0 0 0];

internalField uniform 0.;


boundaryField
{
        front
        {
                type cyclic;
        }

        in
        {
                type zeroGradient;
        }

        out
        {
                type fixedValue;
                value uniform 0.;
        }


        wallup
        {
                type zeroGradient;
        }

        walldown
        {
                type zeroGradient;
        }

        back
        {
                type cyclic;
        }



}
Code:
FoamFile
{
    version    2.0;
    format      ascii;
    class      volScalarField;
    location    "0";
    object      nut;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 2 -1 0 0 0 0];

internalField  uniform 0;

boundaryField
{
    in
    {
        type            zeroGradient;

    }

    out
    {
        type            zeroGradient;

    }

    wallup
    {
        type            zeroGradient;
    }

    walldown
    {
        type            zeroGradient;
    }


    front
    {
        type            cyclic;
    }

    back
    {
        type            cyclic;
    }
}
Code:
FoamFile
{
    version    2.0;
    format      ascii;
    class      dictionary;
    location    "system";
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default        backward;
}

gradSchemes
{
    default        Gauss linear;
    grad(U)        Gauss linear;
}

divSchemes
{
    default        none;
    div(phi,U)      Gauss linearUpwind grad(U);
    div(phi,k)      Gauss limitedLinear 1;
    div(phi,B)      Gauss limitedLinear 1;
    div(phi,nuTilda) Gauss limitedLinear 1;
    div(B)          Gauss linear;
    div((nuEff*dev2(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
    default        Gauss linear corrected;
}

interpolationSchemes
{
    default        linear;
}

snGradSchemes
{
    default        corrected;
}
Code:
FoamFile
{
    version    2.0;
    format      ascii;
    class      dictionary;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    p
    {
        solver          PCG;
        preconditioner  DIC;
        tolerance      1e-7;
        relTol          0.01;

    }

    pFinal
    {
        solver PCG;
        preconditioner  DIC;
        tolerance      1e-08;
        relTol          0;
    }

    "(U|k|nuTilda)"
    {
        solver          smoothSolver;
        smoother        GaussSeidel;
        tolerance      1e-05;
        relTol          0;
    }


}

PISO
{
    nCorrectors    2;
    nNonOrthogonalCorrectors 0;
}
Code:
FoamFile
{
    version    2.0;
    format      ascii;
    class      dictionary;
    location    "constant";
    object      turbulenceProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

simulationType LES;

LES
{
    LESModel        WALE;

    turbulence      on;

    printCoeffs    on;

    delta          cubeRootVol;


    WALECoeffs
    {
                  Cw 0.5;
    }


    cubeRootVolCoeffs
    {
        deltaCoeff      1;
    }

}

I really appreciate any help and advice

HPE February 12, 2020 18:08
Can you share also the mesh and the benchmark data?

navidmt February 13, 2020 05:37
5 Attachment(s)
Quote:
Originally Posted by HPE (Post 757947)
Can you share also the mesh and the benchmark data?
Hi and thanks for reply. Below you can find some photos of my mesh:
my mesh is having almost 30 mil number of cells and is fully unstructured mesh. In third dimension it has 48 layers.
As i mentioned before, the minimum size of the cell around the wall is small enough to have y+<1.

Attachment 74804

Attachment 74805

Attachment 74806

Attachment 74807

Attachment 74808

HPE February 13, 2020 16:19
It is still difficult to follow the question. We dont know what and to which extent you have the differences between the benchmark and the simulation, for example. We dont know how you did postprocess the simulation outcome. etc etc etc

I am just giving examples, rather than trying to know these.

Santiago February 16, 2020 12:55
The first thing I would suggest you is to make a structured grid, with the appropriate boundary layer resolution near the wall (at least 7 points within the viscous layer). the geometry is too trivial, and using triangular meshes may reduce the order of approximation of the interpolation of gradients and the calculation of gradients themselves. If you insist on the road of triangular meshes, make at least sure you are using leasSquares schemes for the calculation of gradients. One additional thing: stabilizing the solution via blending (linearUpwind) breaks the conservation property of the advection term. This means you're "losing" energy....

navidmt February 16, 2020 22:55
Quote:
Originally Posted by Santiago (Post 758313)
The first thing I would suggest you is to make a structured grid, with the appropriate boundary layer resolution near the wall (at least 7 points within the viscous layer). the geometry is too trivial, and using triangular meshes may reduce the order of approximation of the interpolation of gradients and the calculation of gradients themselves. If you insist on the road of triangular meshes, make at least sure you are using leasSquares schemes for the calculation of gradients. One additional thing: stabilizing the solution via blending (linearUpwind) breaks the conservation property of the advection term. This means you're "losing" energy....
Hi, Thank you for your suggestions, I will check it, but how about using hybrid mesh? is it gonna work ? I want to add structured mesh around the airfoil and keep the rest the same!
Another question is which schemes exactly are you suggesting if I end up using triangular mesh ?

Thank you again for your help


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