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-   -   Relaxation Factor Influence (https://www.cfd-online.com/Forums/openfoam/69808-relaxation-factor-influence.html)

 Benoit November 5, 2009 06:58

Relaxation Factor Influence

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Hi FOAMers,

I'm a new user of OpenFoam and I'm currently working on an airfoil in 2D.
When changing the relaxation factor, I have noticed that it also changed the final result so I have made a quick investigation on this problem.
The figure attached displays the drag coefficient computed by OpenFoam. I'm using simpleFoam and the only differences between these cases are the relaxation factors.

Though the differences are small, they do exist and this is certainly not something I was expecting.

Could anyone enlighten me ?
Any help is welcome.

Thanks,

Benoit

Can you post which settings you used per line on the graph?

 Benoit November 5, 2009 08:51

Sure, here are the relaxation factors i used:

green:
p: 0.4
U: 0.8
nuTilda: 0.8

Black:
p: 0.3
U: 0.7
nuTilda: 0.7

Blue:
p: 0.2
U: 0.5
nuTilda: 0.5

Red:
p: 0.1
U: 0.2
nuTilda: 0.2

Do you need anything else ?

 alberto November 6, 2009 23:42

Quote:
 Originally Posted by Benoit (Post 235201) Sure, here are the relaxation factors i used: green: p: 0.4 U: 0.8 nuTilda: 0.8 Black: p: 0.3 U: 0.7 nuTilda: 0.7 Blue: p: 0.2 U: 0.5 nuTilda: 0.5 Red: p: 0.1 U: 0.2 nuTilda: 0.2 Do you need anything else ?
Two suggested experiments:
• What happens using a relaxation factor bigger for p than for U. Say 0.6 for p, 0.4 for U?
• Can you obtain a converged solution without under-relaxing?
Best,

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