CFD Online Discussion Forums - Issues with swak4Foam gradient

Hi guys,

I am calculating the dissipation of the turbulent kinetic energy with swak4foam. Compared to DNS-Data I got good agreemant in the domain bad a far to high value at the wall. So I tried another version, which I called version 2

Code:

gradUiMeanXjGradUiMeanXj

                {

                        type expressionField;

                        dimension [0 2 -3 0 0 0 0];

                        fieldName "gradUiMeanXjGradUiMeanXj";

                        expression "pow(gradUMean.xx,2) + pow(gradUMean.xy,2) + pow(gradUMean.xz,2) + pow(gradUMean.yx,2) + pow(gradUMean.yy,2) + pow(gradUMean.yz,2) + pow(gradUMean.zx,2) + pow(gradUMean.zy,2) + pow(gradUMean.zz,2)"; //tr=Trace

                        autowrite yes;

                        outputControl outputTime;

                }

This is one term to calculate the dissipation. This version is working good, also in the wall region.

In my first version I calculated e.g. this term

Code:

pow(gradUMean.xx,2)

in that way (version 1)

Code:

pow(grad(UMean.x).x,2)

.

In my eyes both versions are equal but version 1 gives to high values near the wall.

Can someone explain me please what is going wrong?

Thanks in advance

Egge