CFD Online Logo CFD Online URL
Home > Forums > CFX

convergence difficulty

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

LinkBack Thread Tools Display Modes
Old   March 2, 2004, 00:20
Default convergence difficulty
Posts: n/a
hi, all

I got some trouble in using CFX-4.4. How to get good convergence? The value of H(enthalpy) is difficult to converge. The residual of H is from 1E+01 to 1.5E-01, and oscillate between 1E+00 and 1E-01. Is this phenomenon correct ? I've tried to use double precision and relaxtion factor, but it doesn't work. How to improve it ? Thank you for your help!!
  Reply With Quote

Old   March 2, 2004, 19:42
Default Re: convergence difficulty
Posts: n/a
Typically, because H = Cp * T (roughly), enthalpy values are on the order of 10^6. Inlet and wall flux values can be even larger. If you're residuals are between 0.1 and 1, that's pretty small compared with the flux values and you may just be hitting the machine round off.

Make sure you're setting your enthalpy reference temperature to just below your expected lowest temperature in the model. This will ensure that H = Cp*[T-Tref] will be as small as it can be without going negative and losing diagonal dominance in the matrix.

Then evaluate your total residual as a fraction of the total heat flux into the model. Something like 1/10^6 or 0.0001% is actually pretty good.

  Reply With Quote


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
Convergence Centurion2011 FLUENT 44 June 20, 2017 09:57
Force can not converge colopolo CFX 13 October 4, 2011 22:03
Convergence of CFX field in FSI analysis nasdak CFX 2 June 29, 2009 01:17
Convergence difficulty in modeling evaporation Lawrence J CFX 0 November 30, 2004 10:08
Convergence Difficulty Sankalp CFX 0 September 27, 2004 17:32

All times are GMT -4. The time now is 00:21.