# Relaxation Factor Influence

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November 5, 2009, 06:58
Relaxation Factor Influence
#1
New Member

Benoit Bonnal
Join Date: Nov 2009
Posts: 2
Rep Power: 0
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
Attached Images
 RelaxationFactor.jpg (29.4 KB, 119 views)

 November 5, 2009, 07:13 #2 Senior Member   Anonymous Join Date: Mar 2009 Posts: 110 Rep Power: 13 Can you post which settings you used per line on the graph?

 November 5, 2009, 08:51 #3 New Member   Benoit Bonnal Join Date: Nov 2009 Posts: 2 Rep Power: 0 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 ?

November 6, 2009, 23:42
#4
Senior Member

Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,912
Rep Power: 32
Quote:
 Originally Posted by Benoit 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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Alberto Passalacqua

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