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-   -   Courant Number Limit, CFL criterion (http://www.cfd-online.com/Forums/openfoam-solving/66934-courant-number-limit-cfl-criterion.html)

barath.ezhilan July 28, 2009 16:52

Courant Number Limit, CFL criterion
 
Hi All,

I am currently simulating vortex breakdown in a conical diffuser and am doing unsteady simulations using transientSimpleFoam and LAunderGibsonRSTM model.

I have a doubt. The generally suggested criteria that CFL<1, is it the Courant Number mean value or the max courant number value???

I have a mean Courant Number of close to 0.13 and Maximum Courant Number of close to 7.

(Courant Number mean: 0.130184 max: 7.10512 velocity magnitude: 3.59437)

And I am able to capture the vortex. (URANS using conventional k-e and k-w models dont work!!!!)

Is it the correct solution that I have got or is the solution unphysical as the CFL condition states??

And my epsilon values blow up beyond bounds after some point. However I set things rite, by reducing the UnderRelaxation Factor.

Is the blow of epsilon related to CFL condition being violated?? Is my method of randomly changing the underrelaxation factor to achieve convergence rite??

Please help me out!!!!!

Regards,
Barath Ezhilan.

bernarde November 2, 2009 05:36

Hi Barath

Have you had any success with your simulation? I'm looking at a similar type of simulation (vortex flow in a tube). I would like to share some ideas if you are still working on this.

Regards

Bernard

maysmech September 24, 2010 07:48

Quote:

I have a doubt. The generally suggested criteria that CFL<1, is it the Courant Number mean value or the max courant number value???
hello,

i have same question. i am seeking Co limit for RAS and LES using pisoFoam.


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