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February 28, 2011, 12:17 
simpleFoam Convergence Stalling

#1 
Member
Greg Givogue
Join Date: Aug 2010
Location: Ottawa Canada
Posts: 57
Rep Power: 7 
Hi,
I've been trying to model an aircraft external tank using simpleFoam. When the flow is axial (xdirection only) simpleFoam convergences <1e6 on all initial residuals and the forces compare well with experimental results. When I change the flow so that it is nonaxial (10 deg of angle of attack and 15 deg of side slip), simpleFoam does not converge <1.4 e5 and the drag values are 3 or 4 times greater than expected. The only thing that I change between the axial and nonaxial conditions are the domain patches (rectangular domain with 6 patches). For the axial case I have 1 inlet patch and 1 outlet patch. For the nonaxial case I have 3 inlet patches and 2 outlet patches. I have set the patch that the pod pylon rests against as type slip. Geometry  35cm diameter, 218 cm long, with conical tips Mesh  6M cells, y+=3, growth rate from body of 1.15 (30 layers prisms the rest tets), wake refinement, checkMesh ok Flow  Re=1.77e7, V=121.6m/s, alpha=10 deg, Beta=15 deg Turbulence  Komega SST I have read several of the posts on this subject but I have not been able to find the solution. I'm hoping someone with more experience can point me in the right direction. Thanks in advance  I appreciate your help! Greg 

February 28, 2011, 22:43 

#2 
Member
Greg Givogue
Join Date: Aug 2010
Location: Ottawa Canada
Posts: 57
Rep Power: 7 
Just corrected the KOmegaSST bug in 1.7.1.
Any suggestions on the the convergence problem? Last edited by Greg Givogue; March 1, 2011 at 09:26. 

March 1, 2011, 04:42 

#3 
Senior Member
Felix L.
Join Date: Feb 2010
Location: Hamburg
Posts: 165
Rep Power: 10 
Hello, Greg,
regarding your convergence problems: since this is a blunt body at a high angle of attack and side slip I would expect separation around the body. This separation most probably leads to periodic vortexshedding behind the body, which clearly is a transient phenomena. Since the SIMPLE algorithm solves the incompressible, steady NS equations, transient flow features can not be captured. Sometimes vortex shedding can be identified by oscillating residuals but usually simpleFoam simply doesn't converge when seeking for a steady solution on an actually transient configuration. Greetings, Felix. 

March 1, 2011, 10:04 

#4 
Member
Greg Givogue
Join Date: Aug 2010
Location: Ottawa Canada
Posts: 57
Rep Power: 7 
Thanks Felix for responding so quickly. I had a feeling that this was the problem and I was in the process of setting up a run with pisoFoam. I'm a CFD rookie and I've never used pisoFoam so I was a bit hesitant going down that path. Before I get completely off track  can you take a look at my fvSchemes and fvSolution files that I'll be using in pisoFoam? Most of the settings I have chosen comes from the tutorials in the pisoFoam folder and my old setup in simpleFoam. What is the best solver to use fvSolution and how about the other settings? How about divSchemes?
Thanks so much and I really appreciate your help! 

March 1, 2011, 13:02 

#5 
Member
Greg Givogue
Join Date: Aug 2010
Location: Ottawa Canada
Posts: 57
Rep Power: 7 
Actually I lied, I'm having issues with wmake and recompiling the solvers after updating the KOmegaSST.C file. I have started a new thread for this... Problem running wmake on simpleFoam
Perhaps someone here will be able to help me with this too... Thanks Problem solved by playing around with permissions... Last edited by Greg Givogue; March 1, 2011 at 13:43. 

March 6, 2011, 13:24 
pisoFoam not converging either

#6 
Member
Greg Givogue
Join Date: Aug 2010
Location: Ottawa Canada
Posts: 57
Rep Power: 7 
Hi Everyone!
Ok, I have reran the problem by first initializing with simpleFoam (1000 iterations) and then running pisoFoam. I get the same problem as before  p fails to converge <10^5 and k converges and diverges. I have attached System files for pisoFoam along with log.pisoFoam files (spilt in 2 for uploading). I am completely stuck now... Thanks! Greg 

March 9, 2011, 21:23 

#7 
Member
Greg Givogue
Join Date: Aug 2010
Location: Ottawa Canada
Posts: 57
Rep Power: 7 
Another problem fixed  my y+ was way to low for using wall functions  should be more like y+>30. Still hoping for suggestions...


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