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-   -   OpenFOAM wall functions (http://www.cfd-online.com/Forums/openfoam-solving/117342-openfoam-wall-functions.html)

Gildeh May 6, 2013 21:34

OpenFOAM wall functions
 
Hello All,

I am working with pisoFoam solver and running several RANS turbulence models (k-e, RNG, ...). I believe that these turbulence models use the standard wall functions for near wall regions. For instance, when I look at inside the nut dictionary at 0 in k-e turbulence modeling, it uses nutkWallFunction. I have two questions:

1. What is this nutkWallFunction exactly (the concept, the formulation, and where can I find the implementation in OF)?

2. How can I change the roughness of the wall function within OpenFOAM? I believe that wall functions must have a roughness coefficient for the model calculation that we should be able to change it. More specifically, I want to see the effect of changing the roughness in my model! How is it possible to change this coefficient?

Thank you for reading this thread and thanks for your time.

Gildeh

fredo490 May 7, 2013 01:14

1) your answer is in the source code:
OpenFOAM-2.1.x / src / turbulenceModels / incompressible / RAS / derivedFvPatchFields / wallFunctions / nutWallFunctions / nutkWallFunction / nutkWallFunctionFvPatchScalarField.H ,gives you:
Code:

Description
    Boundary condition for turbulent (kinematic) viscosity when using wall
    functions, based on turbulence kinetic energy.

and: OpenFOAM-2.1.x / src / turbulenceModels / incompressible / RAS / derivedFvPatchFields / wallFunctions / nutWallFunctions / nutkWallFunction / nutkWallFunctionFvPatchScalarField.C gives you:
Code:

  forAll(nutw, faceI)
    {
        label faceCellI = patch().faceCells()[faceI];

        scalar yPlus = Cmu25*y[faceI]*sqrt(k[faceCellI])/nuw[faceI];

        if (yPlus > yPlusLam_)
        {
            nutw[faceI] = nuw[faceI]*(yPlus*kappa_/log(E_*yPlus) - 1.0);
        }
    }

    return tnutw;

The source can also be found here:
https://github.com/OpenFOAM/OpenFOAM...hScalarField.H

2) check the relative wall function for rough wall. You will find the description in the .H file and the formula used in the .C file.

fredo490 May 7, 2013 01:53

I just saw your answer while I was doing another research:
http://foam.sourceforge.net/docs/cpp/a01446.html


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