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Flow around airfoil using WALE LES model, why Cp and Cf are not correct?

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Old   February 12, 2020, 18:57
Default Flow around airfoil using WALE LES model, why Cp and Cf are not correct?
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navid toussi
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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
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Old   February 12, 2020, 19:08
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HPE
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Can you share also the mesh and the benchmark data?
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HPE

The OpenFOAM community is the biggest contributor to OpenFOAM; not person A or B. Let's report bugs or issue feature requests in GitLab-OpenFOAM.

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How to create a Minimal, Reproducible Example,
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Old   February 13, 2020, 06:37
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navid toussi
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Quote:
Originally Posted by HPE View Post
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.

a.png

b.jpg

c.jpg

d.jpg

e.jpg
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Old   February 13, 2020, 17:19
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HPE
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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.
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Kind regards,
HPE

The OpenFOAM community is the biggest contributor to OpenFOAM; not person A or B. Let's report bugs or issue feature requests in GitLab-OpenFOAM.

Please `design` your questions well. Such effort always pays off well for inquirers and `helpmate`s:
How to create a Minimal, Reproducible Example,
How to give enough info to get help.
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Old   February 16, 2020, 13:55
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Santiago Lopez Castano
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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....
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Old   February 16, 2020, 23:55
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navid toussi
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Quote:
Originally Posted by Santiago View Post
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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