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

residuals and convergence

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 24, 2017, 04:28
Default residuals and convergence
  #1
New Member
 
manar
Join Date: Oct 2016
Posts: 17
Rep Power: 2
manar is on a distinguished road
Hello everyone
I am modeling an air free burning dc arc , I got some results from simulations but I am not 100% sure that I can rely on since the continuity residual is relatively high (attached picture2), I tried to monitor the total temperature (volume weighted average ) which is stable after multi thousands of iterations (attached picture 1) .
my question : can I consider these results , Or I should insist to reduce the continuity residual (URf already reduced - mesh refined ) ? I am suffering because the arc modeling is very touchy since no inlet and outlets ?
Attached Images
File Type: png ???.png (25.5 KB, 30 views)
File Type: png ???ss.png (28.2 KB, 34 views)
manar is offline   Reply With Quote

Old   January 25, 2017, 14:20
Default
  #2
New Member
 
Felipe Costa
Join Date: Jan 2017
Posts: 4
Rep Power: 2
grapheeene is on a distinguished road
N-S Residuals are very very high.

If you had already reduced URF for continuity I suggest to converge momentum (and, maybe, energy) only.. Maybe your viscous model is not the right one for your situation. And then add Species or other phenomena.
grapheeene is offline   Reply With Quote

Old   January 25, 2017, 22:31
Default
  #3
New Member
 
manar
Join Date: Oct 2016
Posts: 17
Rep Power: 2
manar is on a distinguished road
Hi Grapheeene
I cant solve flow equation alone because originally a virtual temperature would ignite the arc which is due to a UDS applying electric current in on of the electrodes ,after the arc is ignited , an electric current would conduct causing some forces to the momentum equation , so all the equations are linked simultaneously . can you explain more about the species ?
or if there any way way to decrease the continuity residual? what about the integral volume , I see it is stable ? is it not enough ?
manar is offline   Reply With Quote

Old   January 26, 2017, 02:25
Default
  #4
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 1,886
Rep Power: 26
LuckyTran will become famous soon enoughLuckyTran will become famous soon enough
I always ignore the continuity residual because it's rather meaningless. It's normalized by the worst value during the first 5 iterations. If your initial guess is perfect, continuity is stuck at 1. If your initial guess is terrible, continuity residual goes up even though the solution gets better. You can test the first case rather easily by simply clearing the stored residuals, if your simulation is already converged the continuity residual will be stuck at 1.
LuckyTran is offline   Reply With Quote

Old   January 26, 2017, 02:40
Default
  #5
New Member
 
manar
Join Date: Oct 2016
Posts: 17
Rep Power: 2
manar is on a distinguished road
Dear LuckyTran
that's what happening to me right now , the continuity residual is stuck at 7.6e-1 though other residuals are below 1e-3 , and volume average (temperature
) is stable .
manar is offline   Reply With Quote

Old   February 15, 2017, 12:12
Default Convergence_criteria
  #6
New Member
 
neha sharma
Join Date: Oct 2016
Posts: 6
Rep Power: 2
neha03sharma is on a distinguished road
Currently I am doing a steady state simulation in ANSYS-CFX. The geometry is a human face with respirator at the face, so it's a little complicated geometry. I am having issues with convergence. Please see the attached image, can I consider it as a converged solution.

In the second image, I am tracking velocity at a random point at outlet.

PLEASE REPLY
RESIDUAL_CONVERGENCE.PNG

VELOCITY@outlet.PNG
neha03sharma is offline   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 44 June 20, 2017 09:57
Convergence issue- residuals of continuity s.garg FLUENT 4 November 7, 2016 12:39
judging convergence through residuals MachZero Main CFD Forum 7 December 25, 2012 13:18
convergence and residuals ebm CFX 2 February 2, 2009 18:55
Convergence - scaled vs unscaled residuals HS FLUENT 1 November 7, 2005 06:45


All times are GMT -4. The time now is 03:47.