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Not converging flow around cylinder with Re=1000000. Help please!

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Old   December 3, 2010, 10:50
Default Not converging flow around cylinder with Re=1000000. Help please!
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Witold
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Dear all,

I am doing my Diplomathesis with ANSYS. I need to simulate a flow around a cylinder as in the Karman vortex street. It is a 3d simulation at a reynolds number of 10^6, which I know is very high. To validate my mesh, I made a smoth mesh with N_x1=42, N_x2=980, N_y=42, N_z=12 and N_diag=42 nodes. The geometry has a hight of 20mm a depth of 10mm and a length of 1000mm. The diameter of the cylinder is 5mm. Please have a look at this image. The medium-fine mesh is the fine one scaled with a factor of 0.5. So is the rough mesh 0.5 times the medium-fine.
I have huge problmes because the simulation will not converge. Only the rough net with a "Reynolds Stress" turbulence model converged in few timesteps. The residuals of the finer meshes jitter around at about 10^(-2) for hours.
Because I do not know, what is relevant for deeper explanation, I linked the [url]result- and the outputfile here CLICK.
I already tried to modify the "Time Scale" to see, if there is an amortisation by changing it. I made the simulations with the "SST" model (Zylinder_3d_re1000000_stat_g_001), changed it for once in "Reynolds Stress" (Zylinder_3d_re1000000_stat_g_004). The file001 did not converged but had a minimal MAX Residual of 10^(-4). File004 converged imidiatly (the cause, it goes a long way straight before, is because I had an "maximum Timescale" activeted. When I deactivated it, it went right down to 10^(-6).

I would appreciate it very much, if someone would have a look at this. This case must be very simple, so there must be something trivial I do not see!

Thank you very much. If there are more files or explanations needed, please ask!

Greetings
Witold
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