[Variation of the solution as the time step varies. RANS/Channel/Moser]
While testing the differents two equations eddy viscosity models with pisoFoam (modified) on a channel I experienced difficulties.
With the k-w models, the converged mean profile and turbulent kinetic energy are time steps dependent. According to this, I would expect better results as I reduce the time step, or it is the reverse. As the time step is reduced the wall shear stress decreases and therefore the pressure drop I apply (to maintain a constant mass flux over my stream-wise periodic length). Result is that the Re_tau is way to low... Target Re_tau is 395 as in Moser simulations.
The corresponding tau_wall and Re_tau is given in the table below (as a function of the time step):
Uploaded with ImageShack.us
Does anyone experienced such results with the k-w and k-w SST models?
My mesh is refined in the near wall region and I am using omegaWallfunction to provide proper boundary conditions to omega.
PS: I am not observing the same behavior with "resolved" (without wallFunctions) LaunderSharmaLowKE. I therefore suspect the trouble from the boundary condition of omega or the numerics...
I'm using OpenFoam 1.6.x
any insight? :) I am really confused now...
Is it a good idea to increase to bulk velocity in order to obtain the right wall shear stress? I guess not....
|All times are GMT -4. The time now is 22:21.|