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-   -   HELP! Diverging Solution for Incompressible Prob. (http://www.cfd-online.com/Forums/fluent/40597-help-diverging-solution-incompressible-prob.html)

Bob April 16, 2006 01:58

HELP! Diverging Solution for Incompressible Prob.
 
Please help! I am trying to finish up this project so that I can graduate in June! I am modeling half an aircraft at incompressible flight speeds and have tried to get the Spalart-Allmaras model to work for higher angle of attack cases, but my solution diverges after 9-10 iterations each time. I have ran an inviscid solution on the same grid and got a converged solution after a little more than 400 iterations that seemed reasonable. I have a feeling that it may be caused by some highly skewed cells present in the mesh. Is this correct? I have tried to minimize the number of highly skewed cells as much as possible, but can't seem to completely get rid of them. Would anyone be willing to look at my mesh in GAMBIT and give me advise? I would greatly appreciate it. I unfortunately do not have access to TGrid. Please email me for more details on the problem and things that I have tried. Thank you so much for any help!!!

Joe April 16, 2006 13:44

Re: HELP! Diverging Solution for Incompressible Pr
 
Use size functions throughout your domain and also resolve the boundary layer with hex/quad (not tri) elements.

Bob April 16, 2006 15:44

Re: HELP! Diverging Solution for Incompressible Pr
 
I'm using a curvature size function for the aircraft body surfaces and a meshed size function for the flow volume with the aircraft faces as sources. I fixed the skewness problem early this morning (found a ver small sliver that contained a bunch of skewed elements), so hopefully that will help. Any suggestions on using GAMBIT for the boundary layer versus adapting the grid in FLUENT? Any advice for either approach? Thank you!!

Joe April 16, 2006 19:33

Re: HELP! Diverging Solution for Incompressible Pr
 
If using a fixed BL, do not exceed an aspect ratio of 1 : 1.2.


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