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

Easy question about residuals

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

Reply
 
LinkBack Thread Tools Display Modes
Old   February 25, 2006, 07:20
Default Easy question about residuals
  #1
Freeman
Guest
 
Posts: n/a
Hi all!

I've sometimes read posts asking why residuals don't go down as far as expected and the asnwer is that this could be due to (scaled) residuals are based in the initial solution and if it is good enough, residuals won't decrease so much.

Now imagine the following situation: I run a simulation in 1st order discretization schemes until I reach a continuity residual of 1e-4 after 200-300 iterations. Then, I switch to 2nd order schemes and I continue my simulation until it is converged (all parameters like residuals, Cd, Cl, mass-weighted avg... remain more or less constant), but now continuity residual is higher than 1e-3: is this because this last residual is calculated from the solution I got in the 1st order simulation and, so, residual cannot go down further or simply this high residual show that there's something in the simulation that doesn't work properly?

Many thanks!
  Reply With Quote

Old   February 25, 2006, 07:39
Default Re: Easy question about residuals
  #2
Thomas
Guest
 
Posts: n/a
Scaled residuals are different from normalized residuals. Please check the manual!! The 1st order upwind is much more robust then the 2nd order and originates a more diffusive solution that is numerically better for residuals (chech the manual). Don't look too much at the absolute value of residuals but at their oscillation and relative decrement/increment.
  Reply With Quote

Old   February 27, 2006, 00:03
Default Re: Easy question about residuals
  #3
rener
Guest
 
Posts: n/a
dfadsfa
  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
Assessment of Residuals eRzBeNgEl Main CFD Forum 3 September 4, 2011 14:05
Residual Question RodriguezFatz FLUENT 0 August 19, 2011 07:23
very easy question: a routine to calculate L infinity norm HaKu Main CFD Forum 0 May 3, 2011 11:12
Quick and easy QUESTION Freeman Main CFD Forum 12 December 13, 2005 16:00
Easy question Confused Main CFD Forum 4 May 22, 2004 02:14


All times are GMT -4. The time now is 21:27.