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-   -   Courant numer (https://www.cfd-online.com/Forums/openfoam/79717-courant-numer.html)

 inginer September 1, 2010 07:17

Courant numer

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

 colinB September 1, 2010 09:50

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.....

 inginer September 1, 2010 10:42

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

 akidess September 2, 2010 03:25

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.

 sabin.ceuca September 3, 2010 10:55

Quote:
 Originally Posted by inginer (Post 273622) 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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