CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

Why this convergence trend?

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   July 6, 2009, 17:51
Default Why this convergence trend?
  #1
New Member
 
Edgard Espinosa
Join Date: Jun 2009
Posts: 18
Rep Power: 16
eespi002 is on a distinguished road
Hi,

I am doing a 3D model with turbulence ( Realizable k-epsilon model) and I am using default Under Relaxation factors for the first 100 iterations. Then at 101 iteration mark, I switch to lower Under relaxation factors to allow the solution to converge. However, when I switch to lower URF number, the solution proceeds to diverge.

Can anyone explain why this is happening? How many iteration should I allows the solution to go through for a 3D model?

Any response is appreciated.

Pleas see link:
http://i1009.photobucket.com/albums/...onvergence.jpg
eespi002 is offline   Reply With Quote

Old   July 7, 2009, 02:17
Default
  #2
Super Moderator
 
-mAx-'s Avatar
 
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 3,297
Rep Power: 41
-mAx- will become famous soon enough
it diverges (you get an error message) or you have a jump?
The jump is normal, if you let iterate, you should retrieve the convergence
__________________
In memory of my friend Hervé: CFD engineer & freerider
-mAx- is offline   Reply With Quote

Old   July 7, 2009, 09:34
Default
  #3
New Member
 
Edgard Espinosa
Join Date: Jun 2009
Posts: 18
Rep Power: 16
eespi002 is on a distinguished road
Quote:
Originally Posted by -mAx- View Post
it diverges (you get an error message) or you have a jump?
The jump is normal, if you let iterate, you should retrieve the convergence
Thanks -mAx-.

I did get an error message. It states:
Turbulent viscosity limited to viscosity ratio of 1.0000000e+6 in 1cells.

Could this have a large impact on the convergence? Also, typically how many iterations should be given to a 3D-turbulent model?

Thanks in advance.
eespi002 is offline   Reply With Quote

Old   July 7, 2009, 10:04
Default
  #4
Super Moderator
 
-mAx-'s Avatar
 
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 3,297
Rep Power: 41
-mAx- will become famous soon enough
this is not an error message, but a warning.
Let iterate, and check if the number of cells involved in this warning is decreasing (in your cas you just have 1 cell )
There is no typical number of iterations untill convergence.
Monitor a variable you want to compute (drop pressure, force , massflow or whatever) and iterates untill you get a flat curve. Then it means that this has converged.
Check also the residuals charts
__________________
In memory of my friend Hervé: CFD engineer & freerider
-mAx- is offline   Reply With Quote

Old   July 7, 2009, 10:54
Default
  #5
New Member
 
Edgard Espinosa
Join Date: Jun 2009
Posts: 18
Rep Power: 16
eespi002 is on a distinguished road
Thanks again.
eespi002 is offline   Reply With Quote

Reply

Tags
convergence, under relaxation factors

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Convergence of CFX field in FSI analysis nasdak CFX 2 June 29, 2009 02:17
Problems with convergence with an easy system franzdrs Main CFD Forum 0 June 15, 2009 19:17
increasing mesh quality is leading to poor convergence tippo CFX 2 May 5, 2009 11:55
Defect correction and convergence ganesh Main CFD Forum 4 June 30, 2006 15:20
Convergence problems Chetan FLUENT 3 April 15, 2004 20:13


All times are GMT -4. The time now is 09:19.