[Peter85]

Dear Foamers,

I am simulating a simple compressible channel flow, using the rhoSimpleFoam solver and the k-Omega-SST turbulence model.
For postprocessing, I'd like to compute YPlus to validate my grid and the wall shear stress. The Reynolds-number is about 18000.
Also, I calculated Tau_wall and YPlus using correlations to validate my results.
For YPlus at the wall:
I used the Blasius-correlation to calculate Cf (Cf = 0.079 * Re ^(-0.25))
Then I calculated Tau_wall using Cf = Tau_wall / (0.5 * rho_0 * U_0^2).
Using Tau_wall, it was easy to calculate U_tau (= sqrt (Tau_wall/rho)) and yPlus (= U_tau * y/ nu with y = height of the closest cell to the wall, this gives me the y* of the first cell).
For Tau_wall:
Using the Blasius-correlation and calculate Tau as described above.

Unfortunately, the values of yPlus were not even close to the ones given by the openFoam utility, and the values of Tau_wall were different by about 20 percent.

The next approach to solve this problem was to write a program, calculating the wall shear stress using the wall velocity gradient, calculated by wallGradU.
The shear stress is calculated Tau_wall = nu*rho * du/dn, taking du/dn from wallGradU. This results matched the ones calculated with the correlation much better.
(better description of how to calculate wall shear stress can be found here:
http://www.cfd-online.com/Forums/ope...interfoam.html)
Therefore, I assume that wallShearStress and YPlus give wrong values. Unfortunately, I don't know why. I just know that those tools are using the wall models to calculate the values, but I don't know how this works exactly.
Is someone familiar with this problem? Can somebody tell me why these results calculated with this tools are wrong?
I think I read somewhere that those tools are only valid for incompressible flows, but not for compressible ones, is that true?

Does anyone know a tool to calculate YPlus correctly? I need to plot a diagram uplus/yplus, therefore I need the exact values.

Thanks,
Peter