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

Courant numer

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

Reply
 
LinkBack Thread Tools Display Modes
Old   September 1, 2010, 07:17
Default Courant numer
  #1
Member
 
inginer's Avatar
 
Ovidiu Michiu
Join Date: Apr 2010
Location: Ingolstadt, Germany
Posts: 52
Rep Power: 7
inginer is on a distinguished road
Hello,

I'm trying to do my first case in OF. I converted a mesh from fluent, an airfoil 2D, compressible flow with M=0.8, Spalart-Allmaras imposed and a Courant Numner=200 in fluent. I adapt an compressible case from tutorials of OF, /sonicFoam/RAS/naca. I can see the mesh without any problems, but I don't know how can I calculate the time step, delta t from /system/controlDict.

The second problem regards the thermophysicalProperties definition. I read the tutorial but when i started to write my thermophysicalPropoperties i got stuck; I have sutherland law imposed and perfect gas; how can i calculate all the coefficients to have a good thermoProp correct?

Thk,

Best Regards,
Ovidiu
inginer is offline   Reply With Quote

Old   September 1, 2010, 09:50
Default
  #2
Senior Member
 
Join Date: Aug 2010
Location: Groningen, The Netherlands
Posts: 216
Rep Power: 9
colinB is on a distinguished road
The courant number is defined like this:

C = (U * delta t) / delta x

with U = velocity of the liquid/ moving wall what ever
delta t you want to calculate
and delta x = domain length [m] / Number of Elements in x direction

for more details see here:

http://www.openfoam.com/docs/user/cavity.php

chapter 2.1.1.4 Control

It happens to be the first tutorial.....
colinB is offline   Reply With Quote

Old   September 1, 2010, 10:42
Default
  #3
Member
 
inginer's Avatar
 
Ovidiu Michiu
Join Date: Apr 2010
Location: Ingolstadt, Germany
Posts: 52
Rep Power: 7
inginer is on a distinguished road
thk colinB,

i check the tutorial before posting the thread.
the problem is that i don't know the cell size, delta x. i receive the mesh from fluent, i didn't do the mesh and i don't have fluent install on my pc to see the cell mesh.

Best,
Ovidiu
inginer is offline   Reply With Quote

Old   September 2, 2010, 03:25
Default
  #4
Senior Member
 
akidess's Avatar
 
Anton Kidess
Join Date: May 2009
Location: Delft, Netherlands
Posts: 919
Rep Power: 17
akidess will become famous soon enough
After conversion you can run checkMesh, and then get information about cell volumes. For a rough estimate of the Courant number you can take the third root of the cell volume.
akidess is offline   Reply With Quote

Old   September 3, 2010, 10:55
Default
  #5
Member
 
Sabin Ceuca
Join Date: Mar 2010
Location: Munich
Posts: 42
Rep Power: 7
sabin.ceuca is on a distinguished road
Quote:
Originally Posted by inginer View Post
the problem is that i don't know the cell size, delta x. i receive the mesh from fluent, i didn't do the mesh and i don't have fluent install on my pc to see the cell mesh.
Hi Ovidiu,
you can actually plot the cell Volumes using the variable mesh.V() and then compute the dx you like best

Ciao,
Sabin
sabin.ceuca 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
RMS Courant Number vs MAX Courant Number zoozoozoo Main CFD Forum 3 June 12, 2012 13:44
Problems with Courant number (LaunderGibsonTurbulence Model) sven OpenFOAM 3 August 10, 2009 03:12
IcoFoam parallel woes msrinath80 OpenFOAM Running, Solving & CFD 9 July 22, 2007 02:58
pls help fluctuating residuals due to courant no sagar CFX 3 March 28, 2006 01:10
Could anybody help me see this error and give help liugx212 OpenFOAM Running, Solving & CFD 3 January 4, 2006 19:07


All times are GMT -4. The time now is 14:19.