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

convergence

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 30, 2006, 23:02
Default convergence
  #1
vijay
Guest
 
Posts: n/a
Hi,

I have a problem while running an unsteady case using coupled implicit scheme. The continuity and x,y,z velocity residuals are fluctuating between a constant minimum and maximum. They are going horizontally and parallely without converging. Does it mean that the grid should be refined further or is there something else to be done? Please suggest.

Thanks in advance
  Reply With Quote

Old   January 30, 2006, 23:57
Default Re: convergence
  #2
Muhammad Shakaib
Guest
 
Posts: n/a
you can try with smaller time steps
  Reply With Quote

Old   January 31, 2006, 01:46
Default Re: convergence
  #3
vijay
Guest
 
Posts: n/a
Hi,

Thanks for ur reply. But I tried with smaller time steps as well. Eventually after coming to the time step I required i.e. smaller time step multiplied with number of time steps, the fluctuations are starting again. Hope u have understood what I mean. Kindly suggest an alternative.

Thanks
  Reply With Quote

Old   January 31, 2006, 06:29
Default Re: convergence
  #4
Muhammad Shakaib
Guest
 
Posts: n/a
What type of fluctuation you have noticed. Typically there is convergence in 20-30 iterations for every time step i.e. residuals drop alteast an order of magnitude and if you have placed a surface monitor it becomes constant in these no. of iterations. Alongwith refining the grid you can test some more things; using different options of solution controls. Also use surface monitors to check whether convergence is acheived for each time step
  Reply With Quote

Old   January 31, 2006, 08:35
Default Re: convergence
  #5
HS
Guest
 
Posts: n/a
Are you sure the minimums and maximums are actually constant? I think the coupled implicit solver can make the residuals look like they're oscillating when they are in fact decreasing over a longer number of iterations (much depending on your Courant number).

/Henrik
  Reply With Quote

Old   January 31, 2006, 11:38
Default Re: convergence
  #6
vijay
Guest
 
Posts: n/a
Hi,

The fluctuations are remaining without any deterioration. Even after large number of iterations they are present. I tried again by refininig the grid but it did not work out. Can u suggest anything?

Thanks
  Reply With Quote

Old   February 1, 2006, 04:04
Default Re: convergence
  #7
kharicha
Guest
 
Posts: n/a
Please refine your boundary layer if you have....not the entire domain. If it doesn't work detail a bit your geometry and phenomena you want to model...
  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
Convergence Centurion2011 FLUENT 24 May 9, 2015 08:02
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
increasing mesh quality is leading to poor convergence tippo CFX 2 May 5, 2009 10:55
Defect correction and convergence ganesh Main CFD Forum 4 June 30, 2006 14:20


All times are GMT -4. The time now is 02:00.