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UNDER-RELAXTATION FACTORS??????????????????

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Old   March 22, 2006, 04:21
Default UNDER-RELAXTATION FACTORS??????????????????
  #1
Anne
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Hello hello everyone. what is the less UNDER-RELAXTATION FACTORS, to put in solution controls. is there a rule to respect?????????????? thanks.

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Old   March 22, 2006, 09:40
Default Re: UNDER-RELAXTATION FACTORS??????????????????
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Nick
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not really , all you are changing is the ratio of values for subsequent interations. The minimum values I tend to put in are of the order of 0.01 , say my solution is blowing up due to temperature I will reduce the energy to that kind of value and maybe back it off a bit when the solution has calmed down.

Obviously the lower the value the slower your solution will take to converge !
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Old   March 24, 2006, 10:03
Default Re: UNDER-RELAXTATION FACTORS??????????????????
  #3
sean
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Hi Nick,

so we can lower the under relaxation factors of all governing equations to such a low value ? In the manual they suggest to reduce, eventually, to about 0.8 the energy equation, 0.2 pressure, 0.5 momentum, k and epsilon.

Thanks for you help,

Best Regards.
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Old   March 24, 2006, 10:10
Default Re: UNDER-RELAXTATION FACTORS??????????????????
  #4
Nick
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yes, I regularly reduce these numbers to such small values, I can't say that I have gone beyond this though. One thing to remeber is that you can do, is to increase the underelaxtion ! Say for example that you have a very stable solution you could well up the pressure to 0.4 or so to speed up the convergence, but this will be very model dependant.

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Old   March 24, 2006, 12:56
Default Re: UNDER-RELAXTATION FACTORS??????????????????
  #5
sean
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ok, thanks a lot!

but, will the solution be affected by choosing so low values of URF?

Regards.

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