CFD Online Logo CFD Online URL
Home > Forums > FLUENT

convergence problem

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

LinkBack Thread Tools Display Modes
Old   May 16, 2003, 07:27
Default convergence problem
Posts: n/a

I'm working on a gas flow throught a thermal exchanger with 3D simulations (400 000 cell). I performed about 10 000 iterations and the residuals are fluctuated around 1.e-03 (velocity and energy) and 5.e-04 (mass conservation). How many iterations more will be necessary for having a converged result ?


  Reply With Quote

Old   May 16, 2003, 08:27
Default Re: convergence problem
Posts: n/a
There isn't an exact number of iteration to obtain a converged solution. However 10000 seems very high. As always, check all boundary conditions and try to underrelax momentum and energy equations.

Anyway, if all conditions of your problem are ok, maybe your initial solution is good, so residuals can't reduce of the quantity you require. You can understand this from residual plotting: if they have been stable for many iterations, maybe this is your case.


  Reply With Quote

Old   May 20, 2003, 00:31
Default Re: convergence problem
Posts: n/a
10000 iterations is a lot.

Could be a couple of reasons. First try lowering the relaxation rates, especially for the energy equation.

If this doesn't work then you may want to try switching to a transient solver (1st-order if you want a steady-state answer). You may have some small fluctuations in your flow, so that no steady-state solution exists. A transient solver also increases the diagonal dominance, and thus the robustness, of the discrete equations. This has often worked for me, even if arriving at a steady-state answer takes a long time.

Hope this helps,

  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 problem when use pisoFoam, LES for wind tunnel case Forrest_Lei OpenFOAM 3 July 19, 2011 06:00
convergence problem commonyue Main CFD Forum 1 December 1, 2009 04:54
Convergence of CFX field in FSI analysis nasdak CFX 2 June 29, 2009 01:17
3D Fluid Flow Convergence problem Emily FLUENT 2 March 21, 2007 23:18
Non Convergence of 3D Heat transfer cfd problem Balraj Main CFD Forum 3 December 9, 2004 01:24

All times are GMT -4. The time now is 21:46.