CFD Online Logo CFD Online URL
Home > Forums > Main CFD Forum

convergence criterion

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

LinkBack Thread Tools Display Modes
Old   June 16, 2000, 09:00
Default convergence criterion
Posts: n/a
I am a new phoenics user, can anybody tell me what is the GLOBAL CONVERGENCE CRITERION (default value 10e-4) that is in the NUMERICS menu? I think it is something linked to the residuals but I don't know how it is calculated, does anybody know?
  Reply With Quote

Old   June 16, 2000, 20:06
Default Re: convergence criterion
John C. Chien
Posts: n/a
(1). Don't try to understand the definition. There is nothing you can do there. (2). When I run a commercial code, I always set these numbers (you are likely to have one for each equation being solved) to 1.0E-08 that is 0.00000001 Then you can set it and forget about it. (2). Use the total number of iterations to control the convergence. Check the variables of interest to you at several locations of interest, and plot the convergence history. (3). The flow convergence (steady state) is non-uniform, at some locations it is fast and at some other locations it is very solw. To reach convergence, you must be able to see flat part of the history plots of the variables vs iteration numbers. (4). Let the computer do the number crunching hard work, and make sure that you have the converged solution. (mesh size and quality always has a great impact on the convergence of the solution) Do not accept the solution unless it is the fully converged solution.
  Reply With Quote

Old   June 18, 2000, 02:43
Default Re: convergence criterion
Posts: n/a
Hi Luca,

global convergence USUALLY refers to a volume integration over the entire domain. So for mass conservation it is the sum of all mass flow rates at the boundaries (and source terms) normalized by the inlet mass flow. So 10e-4 is an overall ballance within 0.01%. This is an indication of how well the nonlinear discrete equations have been solved NOT necessarily of the accuracy of the discrete equations in approximating the solution. 1e-4 is typically for industrial work. It is also important to look at the local residuals how well the individual control volume equations have been solved by the nonlinear iterative process.

Good Luck..................Duane
  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
problem with Min/max rho tH3f0rC3 OpenFOAM 7 February 23, 2013 06:37
Force can not converge colopolo CFX 13 October 4, 2011 22:03
convergence criterion Dominique FLUENT 5 November 24, 2006 03:36
Setting convergence criterion Vidya FLUENT 5 August 6, 2006 16:46

All times are GMT -4. The time now is 17:57.