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

max courant/courant...velocity spikes?

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

Reply
 
LinkBack Thread Tools Display Modes
Old   September 1, 2010, 12:55
Default max courant/courant...velocity spikes?
  #1
New Member
 
Matt James
Join Date: Jun 2010
Location: Marinette,WI, USA
Posts: 25
Rep Power: 5
mdjames is on a distinguished road
Hi all,

I'm running a turbulent half-channel flow (dynSmag). I'm wondering why the max courant number is being reported in the neighborhood of 10-12 while the mean courant is around 0.3, where i calculated it based on expected mean flow.

Where might these wild velocity fluctuations be coming from?

Thanks very much for any help!
mdjames is offline   Reply With Quote

Old   September 17, 2010, 00:59
Default
  #2
Senior Member
 
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,880
Rep Power: 25
alberto will become famous soon enoughalberto will become famous soon enough
Have you very refined cells somewhere in your domain?
__________________
Alberto

GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as live DVD/USB, hard drive image and virtual image.
GeekoCFD 32bit - The 32bit edition of GeekoCFD.
GeekoCFD text mode - A smaller version of GeekoCFD, text-mode only, with only OpenFOAM. Available in a variety of virtual formats.
alberto is offline   Reply With Quote

Old   September 17, 2010, 13:08
Default
  #3
New Member
 
Matt James
Join Date: Jun 2010
Location: Marinette,WI, USA
Posts: 25
Rep Power: 5
mdjames is on a distinguished road
Ah, yes. I have some near wall refinement but only in the wall normal direction. Eddy generation and therefore v and w velocities occurring I suppose?
mdjames is offline   Reply With Quote

Old   September 21, 2010, 15:06
Default
  #4
Senior Member
 
Steven van Haren
Join Date: Aug 2010
Location: The Netherlands
Posts: 149
Rep Power: 5
stevenvanharen is on a distinguished road
Have the same "problem" in my channel flow LES/DNS.

If you are interested you can use the Co utility to determine where the high Courant number appears.
stevenvanharen is offline   Reply With Quote

Old   September 24, 2010, 03:32
Default
  #5
Senior Member
 
maysmech's Avatar
 
Maysam
Join Date: Jan 2010
Posts: 309
Blog Entries: 2
Rep Power: 7
maysmech is on a distinguished road
Hello,
i have two questions.

Quote:
Originally Posted by mdjames View Post
Hi all,

I'm running a turbulent half-channel flow (dynSmag). I'm wondering why the max courant number is being reported in the neighborhood of 10-12 while the mean courant is around 0.3, where i calculated it based on expected mean flow.
How can you find mean courant number? because in terminal min and max courant number is displaying only.



Quote:
Originally Posted by stevenvanharen View Post
Have the same "problem" in my channel flow LES/DNS.

If you are interested you can use the Co utility to determine where the high Courant number appears.
Is it possible to tell more about Co utility?
maysmech is offline   Reply With Quote

Old   September 24, 2010, 04:20
Default
  #6
Senior Member
 
Steven van Haren
Join Date: Aug 2010
Location: The Netherlands
Posts: 149
Rep Power: 5
stevenvanharen is on a distinguished road
Which solver are u using? I get mean and max Co in my terminal window using channelFoam/channelOodles.

Co utility should be in your openfoam folder. Just use Co -help to see how it works.
stevenvanharen is offline   Reply With Quote

Old   September 24, 2010, 05:44
Default
  #7
Senior Member
 
maysmech's Avatar
 
Maysam
Join Date: Jan 2010
Posts: 309
Blog Entries: 2
Rep Power: 7
maysmech is on a distinguished road
Quote:
Originally Posted by stevenvanharen View Post
Which solver are u using? I get mean and max Co in my terminal window using channelFoam/channelOodles.

Co utility should be in your openfoam folder. Just use Co -help to see how it works.
i use pisoFoam. i want solve a rearward facing step with RAS and LES. my problem is i don't know how much can courant be large in solving process. do you know about it?
maysmech is offline   Reply With Quote

Old   September 24, 2010, 06:26
Default
  #8
Senior Member
 
Steven van Haren
Join Date: Aug 2010
Location: The Netherlands
Posts: 149
Rep Power: 5
stevenvanharen is on a distinguished road
RAS, no idea
LES, max CFL ~ 0.5
stevenvanharen is offline   Reply With Quote

Old   September 24, 2010, 09:13
Default
  #9
Senior Member
 
maysmech's Avatar
 
Maysam
Join Date: Jan 2010
Posts: 309
Blog Entries: 2
Rep Power: 7
maysmech is on a distinguished road
Quote:
Originally Posted by stevenvanharen View Post
RAS, no idea
LES, max CFL ~ 0.5
Thanks for your reply.
is it a law for LES or it depends on cases? also please tell your reference.
Best regards.
maysmech 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
Steady pipe flow mean velocity higher than inlet velocity anita OpenFOAM Running, Solving & CFD 7 September 25, 2012 05:35
UDF error - parabolic velocity profile - 3D turbine Zaqie Fluent UDF and Scheme Programming 7 September 23, 2012 03:23
Velocity in Porous medium : HELP! HELP! HELP! Kali Sanjay Phoenics 0 November 6, 2006 06:10
How to calculate Velocity? Kali Sanjay Phoenics 1 May 1, 2006 13:57
what the result is negatif pressure at inlet chong chee nan FLUENT 0 December 29, 2001 05:13


All times are GMT -4. The time now is 16:03.