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

Combustion convergence and URF

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 15, 2004, 07:38
Default Combustion convergence and URF
  #1
Mark
Guest
 
Posts: n/a
Hi,

I have simulated turbulent non-premixed methane/air combustion in a furnace using the standard ke turbulence model and the eddy dissipation combustion model for two-step methane/air mixture.

The solution converges well for 1st order solution with default under-relaxation factors. however the URF's have to be decreased to 0.6 for species and 0.8 for energy in order to get a converged second order solution.

Are these URF's too low to condsider the solution valid?

What effect do these low URF's have on the solution?

Thanks for your help,

Mark
  Reply With Quote

Old   January 15, 2004, 09:18
Default Re: Combustion convergence and URF
  #2
brian
Guest
 
Posts: n/a
The under relaxation factors have no effect on the solution.
  Reply With Quote

Old   January 19, 2004, 22:32
Default Re: Combustion convergence and URF
  #3
Anton
Guest
 
Posts: n/a
The URF's don't have any influence on the final converged solution, but do influence how many iterations it will take to reach that converged solution. In my experience, anything less than 1 for the energy equation takes VERY long to converge. Make sure your solution if fully converged. Monitor certain variables with iteration, in your case, for example, species flow rate and/or temperature at the outlet of your domain is a good one to monitor. If you are satisfied that your solution is not changing very much with further iterations, then consider it converged. Have your residuals flatlined?

I know for the eddy dissipation with multi-species, some under-relaxation below the default is required just to even get the solution TO converge. But, it takes a long time. Try and increase energy, O.8 is far too low. It will take forever to fully converge.
  Reply With Quote

Reply

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
URF and convergence in natural convergence Marie-Anne Main CFD Forum 11 September 11, 2009 11:07
star-ccm+ convergence criteria star Siemens 2 January 14, 2009 05:57
urf rsi Main CFD Forum 0 February 21, 2008 23:27
convergence problem with FLUENT cavitation model Belete Kiflie FLUENT 3 February 20, 2006 11:16
VOF model convergence lana FLUENT 11 October 1, 2005 06:23


All times are GMT -4. The time now is 10:38.