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Old   October 30, 2006, 16:25
Default switching from coupled solver to segregated
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Hello, I have a compressible flow problem which starts with a high Mach number (shock wave, explosion like) and then at later times it turns into a low Mach number problem. I start my fluent solution with coupled solver and confirmed that I am getting 'accurate' results (comparing fluent results with some other FCT solver results) for first ~5-10 usecs. Then when my Mach number decreases (to values ~0.4) I decided to switch to the segregated solver...

when I switched to the segregated solver the results I am getting just after the very first step (even with extremely small time-steps) are totally different than the results till that point with coupled solver... for example the minumum temperature is changing from 298K to ~120K, or gage minimum pressure is decreasing from -5000Pa to -45000Pa...

Please let me know if you have any idea about the possible reasons or solutions to this problem (is there any steps should be taken when switching between the solvers?)

Thanks in advance,
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Old   November 1, 2006, 06:51
Default Re: switching from coupled solver to segregated
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Off hand, the only thing I can think of that would do this is a change to the discretization.

Fluent 6.3 beta has a pressure based coupled solver which is supposed to be good over a much larger range of mach numbers.

Goodluck, Jason
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Old   November 8, 2006, 17:02
Default Re: switching from coupled solver to segregated
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Hey Jason, yes I think it is something to do with discretization and some coefficients stored... I figured if you switch to the segregated solver, turning off the energy temporarily (and UDSs if any) -only for first 1-2 timesteps- then results look fairly close. Thanks
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