CFD Online URL
[Sponsors]
Home > Forums > Main CFD Forum

Converge and diverge

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

Reply
 
LinkBack Thread Tools Display Modes
Old   February 23, 2002, 07:36
Default Converge and diverge
  #1
Jack
Guest
 
Posts: n/a
Hello, everyone,

I am using low-reynolds k-e model to simulate the flows in ducts with periodic condition. The reynolds stress is model by EASM. However, I have difficult to make the program converge. The iterations always oscilate within a certain range. However, the results with the lowest converge critia are very close to the correct solution. Could anybady give me any idea how to improve it?

Thank you very much

Jack
  Reply With Quote

Old   February 23, 2002, 10:14
Default Re: Converge and diverge
  #2
wang
Guest
 
Posts: n/a
As I understand, you use time-dependent solution. What kind of time discretization do you use? or Have you try to ever decrease the time step?
  Reply With Quote

Old   February 24, 2002, 08:02
Default Re: Converge and diverge
  #3
Jack
Guest
 
Posts: n/a
it is a steady state calculation.
  Reply With Quote

Old   February 24, 2002, 09:21
Default Re: Converge and diverge
  #4
wang
Guest
 
Posts: n/a
Hallo Jack,

my first question is, how can you simulate the periodic condition with steady solution?

If your computation is a steady one, and it doesn't converge, it may mean that 1). The solution is an unsteady one, hence you can not get steady solution. There is numerical diffusion that prevents the solution be not diverged. Try a time-dependent solution. 2). Grid quality. It may be that you have some coarse resoltuion at locations where there is strong gradient. Try to check your grid.

hope this help.
  Reply With Quote

Old   February 24, 2002, 23:43
Default Re: Converge and diverge
  #5
john
Guest
 
Posts: n/a
I second to Wang's suggestion on checking your grid. Personally, I had used low Re model in StarCD, and sometimes it never get to the standard convergence criteria. Because I used very fine mesh, and maybe also bad mesh quality, I could pick up turbulence without using turbulence model, to some extent. So, never had a steady state solution.
  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
Converge problem siara817 STAR-CCM+ 13 November 17, 2011 14:47
Laminar doesn't converge; Turbulent models do? Amit FLUENT 10 October 26, 2011 02:12
Converge in Dense meshe, Diverge in less mesh, but correct answer in less mesh!?!? arash_7444 FLUENT 0 December 23, 2009 14:22
CFX converge problem caused by shock waves littlelz CFX 3 August 17, 2009 10:35
Residual doesn't converge and also diverge. akr FLUENT 6 October 17, 2006 08:16


All times are GMT -4. The time now is 07:39.