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

convergence criterion

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   November 16, 2006, 15:31
Default convergence criterion
  #1
Dominique
Guest
 
Posts: n/a
Hi I am wondering if someone can tell me what factors influence the atteinable convergence criterion. I am studying the turbulent flow over a descending step and am having a very hard time getting Fluent to converge. With a K-Epsilon model, and the Enhanced Wall Treatment, the results with a conv. criterion at 10^-4 are not acceptable. With 10^-5, it is better but not yet the right answer. The recirculation zone at the foot of the step is much too small. I even tried to apply a laminar model and still, no convergence with the convergence criterion at 10^-4. All these, with the same mesh.

Can anyone help?? Also, is it normal for k to be more or less 100 times smaller than Epsilon? Thank you in advance!
  Reply With Quote

Old   November 17, 2006, 23:55
Default Re: convergence criterion
  #2
HSeldon
Guest
 
Posts: n/a
Hi, Did you try with the under-relaxation coefficients? And did you try changing the discretization scheme?

Play a bit with them to see what happens.

Take care.
  Reply With Quote

Old   November 19, 2006, 13:47
Default Re: convergence criterion
  #3
Dominique
Guest
 
Posts: n/a
Hi, Well I am starting to play with the under-relaxation coefficients (which is what my professor suggested), but I'm looking for some guiding principles. I tried several discretization schemes and obtain the exact same results every time. Any idea why my laminar results aren't acceptable either? Could it be that I shouldn't be using a pressure outlet (of 0)? My inlet is a constant velocity inlet... Thanks again Dominique
  Reply With Quote

Old   November 23, 2006, 10:06
Default Re: convergence criterion
  #4
RoM
Guest
 
Posts: n/a
Is your inlet far enough away from the step? Maybe the velocity profile needs some more time to develop.

RoM
  Reply With Quote

Old   November 23, 2006, 19:02
Default Re: convergence criterion
  #5
Dominique
Guest
 
Posts: n/a
Well, for now I am using a constant velocity at the entrance. Thanks anyways, any other ideas? Dominique
  Reply With Quote

Old   November 24, 2006, 03:36
Default Re: convergence criterion
  #6
RoM
Guest
 
Posts: n/a
You can use a constant velocity if you dont have a profile but you have to make shure that the inlet is far enought away from the step so that the velocity profile has some time to develop. I think the distance should be at least 10*H where H is the channel height.

RoM
  Reply With Quote

Reply


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 Centurion2011 FLUENT 48 June 15, 2022 00:29
problem with Min/max rho tH3f0rC3 OpenFOAM 8 July 31, 2019 10:48
Force can not converge colopolo CFX 13 October 4, 2011 23:03
Setting convergence criterion Vidya FLUENT 5 August 6, 2006 17:46
Convergence criterion Moose Main CFD Forum 5 June 9, 2005 21:39


All times are GMT -4. The time now is 05:14.