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-   -   what to do when solution doesn't converge? (http://www.cfd-online.com/Forums/cfx/20129-what-do-when-solution-doesnt-converge.html)

Jenny January 27, 2004 08:30

what to do when solution doesn't converge?
 
Hi everyone,

I'm using SST model. My problem is a steady state fully developed turbulent curved duct flow. Outlet is set as opening with zero pressure and inlet with the velocity profile. The solution seems to stop converging after a certain no. of iteration. Can the separation in flow cause the SST model to fail?

http://www.angelfire.com/ab7/cfdwork/RMS.jpg http://www.angelfire.com/ab7/cfdwork/RMS2.jpg http://www.angelfire.com/ab7/cfdwork/RMS3.jpg

Johnson January 27, 2004 10:31

Re: what to do when solution doesn't converge?
 
Hi Jenny

I doubt this is the case. I would suggest looking at your residuals in Post first to see where the maximum values are. I would then examine the resolution of your mesh - very often you may only be able to achieve a certain level of convergence with a certain level of grid refinement.

Johnson

p.s. do you have re-circulation at your outlet ?

Jan Rusås January 27, 2004 12:22

Re: what to do when solution doesn't converge?
 
Nice residual curves! Try to define convergence! When I look at your residual curves I would be satisfied, I cant see your problem. Look in your outfile and check the global balances and see if they also are OK. (22 days left as a CFX user :)

Robin January 27, 2004 13:02

Re: what to do when solution doesn't converge?
 
Hi Jenny,

This doesn't look too bad. You may just be moving through a slow transient, increasing your timestep may help accelerate things.

Regards, Robin

Glenn Horrocks January 27, 2004 16:52

Re: what to do when solution doesn't converge?
 
Hi Jan,

22 days left? Are you moving across to the Dark Side?

Glenn

Jan Rusås January 28, 2004 04:00

Re: what to do when solution doesn't converge?
 
Hi Glenn,

I have decided to sacrifice my self for a period and investigate what is going on at the Dark Side :) (21 days left)


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