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-   -   yplus postProcessing formula (http://www.cfd-online.com/Forums/openfoam-post-processing/116849-yplus-postprocessing-formula.html)

immortality April 26, 2013 08:16

yplus postProcessing formula
 
where does this formula that is used for yPlus come from?!
I have not seen such expression so far but differently.where can I find an article or page about such expression?
Code:

turbulence {
        type executeIfObjectExists;
        objectName k;
        checkType true;
        //        checkType false;
        objectType volScalarField;
        objectShouldExist true;
        //        writeDebug true;
        readDuringConstruction false;

        functions {
            yPlusField
            {
                type expressionField;
                outputControl timeStep;
                outputInterval 1;
                fieldName yPlus;
                expression "pow(0.09,0.25)*sqr(k)*nearDist()/mu";
                autowrite true;
            }
            yPlusWall
            {
                type patchExpression;
                expression "pow(0.09,0.25)*sqr(k)*dist()/mu";
                accumulations (
                    min
                    max
                    average
                );
                patches (wall);
                verbose true;
            }
        }
    }


immortality April 26, 2013 22:18

i have found that this expression is y star not y plus.
How such an obvious mistake has been made here in a tutorial of OpenFOAM?

immortality May 2, 2013 14:18

how can modify it to true expression?very important to me.
(my case is compressible,kOmegaSST turbulence model)

immortality May 5, 2013 08:34

in mutkWallFunctionFvPatchScalarField the equation uses for y-plus is related to y-star not y-plus

Code:

y-star=pow(0.09,0.25)*sqr(k)*nearDist()/mu
Code:

y-plus=rho*u_star*y/mu which u*=aqrt(taw_w/rho)
y-star is related to turbulent kinetic energy while y-plus relates to friction velocity(that relates to wall skin friction in its own)

in the code of mut
:
Code:

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

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

        if (yPlus > yPlusLam_)
        {
            mutw[faceI] = muw[faceI]*(yPlus*kappa_/log(E_*yPlus) - 1);
        }
    }
thanks.


immortality May 5, 2013 11:16

I reported this as a bug:
http://www.openfoam.org/mantisbt/view.php?id=835
could anyone help.the answer is not acceptable to me.I want to know the true yPlus in a turbulent kOmegaSST with yplus<=1 to be sure that separation regions and adverse pressure gradients are calculated and included truely not through some "wall-function rough estimations".
maybe someone dosn't want to use wall functions.
I want "y plus" exactly and only "y plus" not "y star" or any other thing instead of "y plus":mad:
could anyone help?
please don't hesitate.
(I have see some modified files for yPlusRAS but they don't work in 2.2.0 version)


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