CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Running, Solving & CFD

interIsoFoam runs for maxCo = 10 but not maxCo = 2.5

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

Like Tree2Likes
  • 2 Post By Bloerb

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   August 20, 2020, 09:27
Question interIsoFoam runs for maxCo = 10 but not maxCo = 2.5
  #1
New Member
 
Shannon Leakey
Join Date: Mar 2019
Posts: 10
Rep Power: 7
scleakey is on a distinguished road
OpenFOAM uses implicit methods so I thought I would see how far I could push the Courant number before it crashes - isn't the point of implicit methods to get large Courant numbers?

I'm running a multiphase case with interIsoFoam on six processors. Keeping everything else the same, I tried different values for maxCo...

1.0
2.0
2.3
2.5 crashed at t = 0.02 after high residual for p_rgh
2.7 crashed at t = 0.02 after high residual for p_rgh
3.0 crashed at t = 0.02 after high residual for p_rgh
5.0
10.0
20.0 crashed at t = 1.31, not sure exactly why

I don't understand how it ran for maxCo = 10 (with very sensible results) but crashed for maxCo = 2.5? I realise there are lots of reasons that it might crash but I thought that decreasing the Courant number would make it more stable, not less

Has anybody else experienced this?
scleakey is offline   Reply With Quote

Old   August 20, 2020, 15:07
Default
  #2
Senior Member
 
Join Date: Sep 2013
Posts: 353
Rep Power: 20
Bloerb will become famous soon enough
Implicit methods while allowing you to use Co>1 have a smoothing effect on the solution. So high pitched oscillations with a frequency higher than your time step will be smoothed out. This usually means a loss in accuracy. Imagine a sine wave where you only calculate the values between peaks. It is not unreasonable that the same effect applies to errors of said frequency. So depending on your problem this can increase stability in a certain range.
arjun and scleakey like this.
Bloerb is offline   Reply With Quote

Old   August 21, 2020, 04:43
Default
  #3
New Member
 
Shannon Leakey
Join Date: Mar 2019
Posts: 10
Rep Power: 7
scleakey is on a distinguished road
Quote:
Originally Posted by Bloerb View Post
Implicit methods while allowing you to use Co>1 have a smoothing effect on the solution. So high pitched oscillations with a frequency higher than your time step will be smoothed out. This usually means a loss in accuracy. Imagine a sine wave where you only calculate the values between peaks. It is not unreasonable that the same effect applies to errors of said frequency. So depending on your problem this can increase stability in a certain range.
Thanks for your reply I think I understand what you mean
scleakey is offline   Reply With Quote

Reply

Tags
courant number, implicit, interisofoam, maxco, stability

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
from interFoam to interIsoFoam brammekeuh987 OpenFOAM Running, Solving & CFD 2 April 18, 2020 07:52
maxCO doesn't work MagicCFD OpenFOAM Running, Solving & CFD 0 May 14, 2019 02:02
[blockMesh] Another cylinder question bendel_boy OpenFOAM Meshing & Mesh Conversion 5 January 6, 2015 05:09
icoFoam continuity error tellico OpenFOAM 1 September 21, 2011 03:43
weird error during blockMesh SePe OpenFOAM 1 October 25, 2010 10:31


All times are GMT -4. The time now is 11:11.