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[Variation of the solution as the time step varies. RANS/Channel/Moser]

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Old   October 28, 2011, 03:06
Unhappy [Variation of the solution as the time step varies. RANS/Channel/Moser]
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Dear Foamers,


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):





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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

Last edited by tonkiplis; October 28, 2011 at 05:24. Reason: picture size...
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Old   October 29, 2011, 07:09
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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....

Last edited by tonkiplis; October 29, 2011 at 09:57.
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