# Compressible external flow

 Register Blogs Members List Search Today's Posts Mark Forums Read

 October 10, 2003, 18:30 Compressible external flow #1 Rob Guest   Posts: n/a Hello, I am trying to simulate an external compressible flow (M=0.5) over a hemisphere on a flat plate in Fluent 6. I am starting off by simplifying the problem to just a 2-D cylinder atached to a flat plate. So the flow goes along the flat plate then over the 2-d cylinder then along the flat plate again (just for a visual). I can run the case no problem with the air being incompressible, but as soon as I change the density to ideal-gas I get an error message that reads"Error: divergence detected in AMG solver: temperature" and the continuity and energy residuals jump off the charts 10^15. I have tried both the velocity inlet and mass flow rate as a inlet boundary condition and I have the outlet boundary condtion set as a pressure outlet. My grid is a structured grid that is fine, I checked its quality in gambit and the skew is less than 0.1 for all elements. I also tried to run the outter boundaries as pressure far field however since the outter boundaries actually meet the edges of the flat plate that did not work either. Any suggestions on how to get this case to converge would be great. Thank you for your time and I hope to hear from some of you CFD gurus! Rob

 October 15, 2003, 03:58 Re: Compressible external flow #2 Venkatesh V Guest   Posts: n/a Hi Rob, I hope you are solving with default Courant Number. For initial few iterations reduce the courant number. Venkat

 October 15, 2003, 12:55 Re: Compressible external flow #3 Rob Guest   Posts: n/a Hello Venkat, Thank you for the response. I have discovered that reducing the courant number will keep my solution from diverging with using the pressure far field boundary conditions. However the convergence is real slow and the residuals oscillate with a large amplitude. So far I have completed 100,000 iterations and the lowest the residuals have come down to is 5*10^-3. The residuals oscillate between 1*10^-2 and 5*10^-3. So I guess it will be slow going. However if it is this slow with a 2-D case, is it realistic to attempt a 3-D case? Thank you for your response...Rob

 October 29, 2003, 17:16 Re: Compressible external flow #4 Zouhir Guest   Posts: n/a It seems that your outerboundary is very close to the cylinder. Normally, one would extend the outerboundary some 10 to 15 chord lengths away. Also, try visualizing your solution at various time steps to see where the problem is. Another thing you can try is to replace the wall BC upstream and downstream of the cylinder with the symmetry BC. Good luck!

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post BBG Main CFD Forum 1 November 19, 2008 15:05 ryan_m OpenFOAM Running, Solving & CFD 3 April 7, 2008 08:18 rave CD-adapco 7 July 17, 2007 09:48 Pathway0320 FLUENT 1 November 17, 2006 04:37 atit Main CFD Forum 8 July 31, 2000 13:19

All times are GMT -4. The time now is 03:41.