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

very high courant number

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   August 16, 2011, 10:16
Default very high courant number
  #1
New Member
 
Diego Sanz
Join Date: Aug 2011
Posts: 9
Rep Power: 14
dsanza is on a distinguished road
Hi everyone,

i got a newbie question. i'm trying to simulate the turbulent(k-epsilon) transient flow in water channels with the interFoam solver. after +- 0.01 seconds i get courant numbers of up to 7*e-20 delta t 6*e-35

any idea what i am doing wrong? have i chosen the wrong solver?

thnx
dsanza is offline   Reply With Quote

Old   August 16, 2011, 10:27
Default
  #2
Senior Member
 
Kent Wardle
Join Date: Mar 2009
Location: Illinois, USA
Posts: 219
Rep Power: 21
kwardle is on a distinguished road
A little more info would be helpful (BCs, general setup), but chances are that your k and/or epsilon are blowing up. Do you see "bounding k" in the output? Did you initialize them as 0 or something very small (e.g. 1e-11). Small value tends to work better--though I must say I have not worked much with k/epsilon (interFoam is transient anyway so LES has virtually no added cost) but in the little I have done I have found it to be a little unstable for some reason. Have you tried adding relaxation factors for k and epsilon? This is done in system/fvSolution.
kwardle is offline   Reply With Quote

Old   August 17, 2011, 03:29
Default
  #3
New Member
 
Diego Sanz
Join Date: Aug 2011
Posts: 9
Rep Power: 14
dsanza is on a distinguished road
i have a half full water channel, there is no water comming in, just water going out with a constant velocity. i checked what you sugested, and epsilon is grows from 0.01, as initialised to 0.7 in 0.05 seconds. however this happens in the air part of the channel, not in the water.

any sugestions as how to chose the relaxation factors?

i also tried changing the geometry of the channel, if i use a rectangle as a crosssection, everything is ok, when using a circle as a crosssection i get the time problem. is it posible that my mesh is causing it?

thank you very much for your help!
dsanza is offline   Reply With Quote

Reply

Tags
channel flow, courant, courant number increasing

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
Running stably with a large Courant number using pimpleFoam mlawson OpenFOAM 11 November 29, 2014 11:37
LES near wall model & courant number kasim CFX 5 March 16, 2008 19:23
COURANT NUMBER Ferreira Main CFD Forum 23 February 26, 2006 19:10
Could anybody help me see this error and give help liugx212 OpenFOAM Running, Solving & CFD 3 January 4, 2006 19:07
Difficulties in solving a high Reynolds number Flow? wowakai Main CFD Forum 10 December 29, 1998 14:46


All times are GMT -4. The time now is 04:46.