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-   -   Near Wall treatment (http://www.cfd-online.com/Forums/openfoam/68260-near-wall-treatment.html)

sven September 11, 2009 18:32

Near Wall treatment
 
I am using OpenFOAM to calculate a turbulent channel flow with a Reynolds Stress Model using wall functions. Since my results are not quite what they should be, I am interested how OpenFOAM deals with the near wall region, because I think this could be the course for my bad results. So, my questions are:
  1. In which file can I find how the near wall region is treated?
  2. I am especially interested in how the velocity gradient for the cell next to the wall is calculated (which order, with which values), where can I find this?
  3. Where can I get more information on how the wall Functions in OpenFOAM work?
Thanks a lot!

sven September 13, 2009 20:57

I found out that the gradient at the wall is somehow defined in fvPatchField.C. In the source Code of this file, it says:

Code:

// Return gradient at boundary                                                     
template<class Type>
Foam::tmp<Foam::Field<Type> > Foam::fvPatchField<Type>::snGrad() const
{
    return (*this - patchInternalField())*patch_.deltaCoeffs();
}

and I also found the declaration of deltaCoeffs() in the file fvPatch.H:

Code:

//- Return the face - cell distance coeffient                                     
            //  except for coupled patches for which the cell-centre
            //  to coupled-cell-centre distance coeffient is returned
            const scalarField& deltaCoeffs() const;

Unfortunately I do not really understand how the gradient at the boundary is calculated. Does anyone understand this source code and cann tell me how the gradient is calculated?


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