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-   -   Different Under Relaxation Factors (http://www.cfd-online.com/Forums/fluent/34995-different-under-relaxation-factors.html)

Ertan November 4, 2004 11:56

Different Under Relaxation Factors
 
Hello everybody,

My question is, did anyone of you faced with different flow solutions if you keep everything same but only change Under Relaxation Factors?

thank you for contribution...

Michael November 5, 2004 04:47

Re: Different Under Relaxation Factors
 
In my opinion the solution of the problem shouldn't change. If you under-relax you should achieve the same results, however it will need more iterations.

SAM November 5, 2004 05:08

Re: Different Under Relaxation Factors
 
refine ur mesh . is ur mesh fine enough

did u make mesh dependence study


Ertan November 8, 2004 15:13

Re: Different Under Relaxation Factors
 
My mesh is 0.03inches tetrahedral. How can I make mesh dependence study?

SAM November 9, 2004 03:52

Re: Different Under Relaxation Factors
 
number ur number of noded


gts November 10, 2004 13:21

Re: Different Under Relaxation Factors
 
if you use a (very) small under relaxation factor you will have no changes in the solution and you can obtain the steady state. You shoul also try to take lower residuals

ap November 10, 2004 19:38

Re: Different Under Relaxation Factors
 
If you use too small under-relaxation factors you risk to obtain false convergence.

This means that in unsteady calculations, you have a sort of lag between the real flow conditions at a time and the predicted flow condition.

In steady calculations, false convergence means you don't reach the solution.

Under relaxation factors have to be reduced with care, keeping in mind that you just have to reduce them in order to obtain a stable solution.

Hi :)

ap

gts November 11, 2004 05:07

Re: Different Under Relaxation Factors
 
Of course the steady state obtained using a small ur could be a "wrong steady state"


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