# Courant numer

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 September 1, 2010, 07:17 Courant numer #1 Member     Ovidiu Michiu Join Date: Apr 2010 Location: Ingolstadt, Germany Posts: 52 Rep Power: 8 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

 September 1, 2010, 09:50 #2 Senior Member   Join Date: Aug 2010 Location: Groningen, The Netherlands Posts: 216 Rep Power: 11 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.....

 September 1, 2010, 10:42 #3 Member     Ovidiu Michiu Join Date: Apr 2010 Location: Ingolstadt, Germany Posts: 52 Rep Power: 8 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

 September 2, 2010, 03:25 #4 Senior Member     Anton Kidess Join Date: May 2009 Location: Delft, Netherlands Posts: 1,141 Rep Power: 20 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.

September 3, 2010, 10:55
#5
Member

Sabin Ceuca
Join Date: Mar 2010
Location: Munich
Posts: 42
Rep Power: 8
Quote:
 Originally Posted by inginer 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

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