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LES of a square cylinder

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Old   June 24, 2010, 10:22
Question LES of a square cylinder
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Hello,

I am having what I presume are inlet or grid quality issues with an LES case for a square cylinder. As can be seen in the attached images, the inflow to the left of the cylinder shows a strange behaviour with a variation of U (in attached image, coloured by U mag). My initial guess was that the aspect ratio or the grid quality overall is not good enough for LES. My grid does pass all checks inside of checkMesh.

I am using the dynamic Smagorinsky model (simple filter and cubeRootVol delta) with a hex + polyhedra (due to local refinement) grid of ~1.6 million cells. The Re = 22,000 and y+ average = ~6 after approximately 20 non-dimensional flow-overs, which I presume could be an issue as well as I am using the nuSgsWallFunction on the cylinder wall patch. I will try to construct a y+=1 grid and avoid the use of wall functions next.

My nuSgs file:
Code:
dimensions      [0 2 -1 0 0 0 0];

internalField   uniform 0;

boundaryField
{
    inlet
    {
        type            zeroGradient;
    }

    outlet
    {
        type            zeroGradient;
    }

    sides
    {
        type            cyclic;
    }

    cyl
    {
//        type            zeroGradient;
        type            nuSgsWallFunction;
        value           uniform 1;
    }

    sym
    {
        type            symmetryPlane;
    }
}
And my 0/U file:
Code:
dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0.022 0 0);

boundaryField
{
    cyl
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
    inlet
    {
        type            fixedValue;
        value           uniform (0.022 0 0);
    }
    outlet
    {
        type            zeroGradient;
    }
    sides
    {
        type            cyclic;
    }
    sym
    {
        type            symmetryPlane;
    }
}
Is my setup incorrect, or is this purely a grid issue? Any hints would be greatly appreciated.


-Grzegorz
Attached Images
File Type: jpg flow2.jpg (20.8 KB, 182 views)
File Type: jpg grid2.jpg (59.2 KB, 194 views)
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Old   June 24, 2010, 12:33
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Daniel WEI (老魏)
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Sorry, but I have to say your mesh looks bad, and is better not be called LES.

And what's more, it seems your inlet has a velocity profile, that's strange, isn't it?

You can upload your case file in tgz format, so that we could have a look, we need 0/ constant/ system/
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