[immortality]

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?

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;
            }
        }
    }