CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM

Relaxation Factor Influence

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   November 5, 2009, 06:58
Default Relaxation Factor Influence
  #1
New Member
 
Benoit Bonnal
Join Date: Nov 2009
Posts: 2
Rep Power: 0
Benoit is on a distinguished road
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
File Type: jpg RelaxationFactor.jpg (29.4 KB, 104 views)
Benoit is offline   Reply With Quote

Old   November 5, 2009, 07:13
Default
  #2
Senior Member
 
Anonymous
Join Date: Mar 2009
Posts: 110
Rep Power: 7
madad2005 is on a distinguished road
Can you post which settings you used per line on the graph?
madad2005 is offline   Reply With Quote

Old   November 5, 2009, 08:51
Default
  #3
New Member
 
Benoit Bonnal
Join Date: Nov 2009
Posts: 2
Rep Power: 0
Benoit is on a distinguished road
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 ?

Benoit is offline   Reply With Quote

Old   November 6, 2009, 23:42
Default
  #4
Senior Member
 
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,890
Rep Power: 25
alberto will become famous soon enoughalberto will become famous soon enough
Quote:
Originally Posted by Benoit View Post
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,
__________________
Alberto

GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as live DVD/USB, hard drive image and virtual image.
GeekoCFD 32bit - The 32bit edition of GeekoCFD.
GeekoCFD text mode - A smaller version of GeekoCFD, text-mode only, with only OpenFOAM. Available in a variety of virtual formats.
alberto is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Relaxation and convergence sammi Phoenics 0 March 20, 2008 05:32
Relaxation Factors Tim Phoenics 3 June 30, 2004 03:03
relaxation parameter rvndr Main CFD Forum 0 May 5, 2004 13:34
Question on adjusting relaxation factor CFD Rookie Main CFD Forum 3 January 26, 2004 15:37
Relaxation factor Moon CD-adapco 1 June 13, 2003 12:13


All times are GMT -4. The time now is 13:28.