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

Convergence with coupled implicit solver

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 28, 2005, 08:47
Default Convergence with coupled implicit solver
  #1
Henrik Ström
Guest
 
Posts: n/a
Hello!

I have an unsteady simulation that I have run earlier versions of using the segregated solver, and that worked just fine. However, now I want to add a very fast chemical reaction to my system, which will make the problem stiff. This causes the segregated solver to have problems as the reaction starts after a few hundred timesteps. I therefore want to change to the coupled (implicit) solver and also possibly use the special stiff-chemistry ODE solver that is built-in in the coupled solver.

My problem is, though, that when I change to the coupled solver, the solution diverges already in the first timestep (that is, before the reaction even takes place and for a situation where the segregated solver still works OK)... So, what can I do to get it to work? I have tried very low Courant numbers, but that does not seem to help (only slow down the rate at which it diverges). Are there any other parameters that I should experiment with? (FAS in the explicit formulation is not applicable since it is an unsteady simulation).

Any help or hints is greatly appreciated!

Thanks, Henrik
  Reply With Quote

Old   October 29, 2005, 03:57
Default Re: Convergence with coupled implicit solver
  #2
nasser
Guest
 
Posts: n/a
Hi 1-use very small time step for first itration 2-use very small cournt number in first 3-enable stiff model 4- refine your mesh goodbye
  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
Coupled PDEs solver wanted navi.vonavi_1874 OpenFOAM Running, Solving & CFD 1 November 5, 2010 11:48
Problem with Coupled Solver! Parag Gadgil Main CFD Forum 2 December 20, 2007 14:02
Transient UDS with coupled solver Dmitriy Makarov FLUENT 1 February 9, 2007 18:06
switching from coupled solver to segregated Oz FLUENT 2 November 8, 2006 17:02
Can I use coupled solver for this problem Frank FLUENT 0 April 11, 2006 06:28


All times are GMT -4. The time now is 07:28.