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Old   April 26, 2013, 08:16
Default yplus postProcessing formula
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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;
            }
        }
    }
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Old   April 26, 2013, 22:18
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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?
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Old   May 2, 2013, 14:18
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how can modify it to true expression?very important to me.
(my case is compressible,kOmegaSST turbulence model)
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Old   May 5, 2013, 08:34
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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.
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Old   May 5, 2013, 11:16
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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"
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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