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 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?

Gildeh

 fredo490 May 7, 2013 01:14

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