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-   -   question to courant criterion (http://www.cfd-online.com/Forums/openfoam/88245-question-courant-criterion.html)

 tH3f0rC3 May 12, 2011 02:16

question to courant criterion

Hi,

does someone know how the courant criterion is used in OpenFoam?
I'm using the chtMultiRegionFoam (transient-version).
Does the solver fit the time step according to the criterion? Thus, the time step isn't constant during the simulation?

Best Regards,
tH3f0rC3

 tH3f0rC3 May 12, 2011 07:08

I have just recognized that it is possible to set the time step also to delta t = 0.1

Best Regards,
tH3f0rC3

 tH3f0rC3 May 16, 2011 02:22

Hi,

can I use relaxationFactors for a transient solver like chtMultiRegionFoam?
I have read here that this doesn't work. But I don't understand why?
There is also mentioned that a simpletransient-Solver can work with relaxationFactors. But what is the transientsimple-Solver? Is this solver still calculating a transient case?

Best Regards,
Dirk

 akidess May 16, 2011 03:27

Relaxation only applies to the SIMPLE algorithm, whereas most transient solvers in openFoam use PISO. A combination of both algorithms is called PIMPLE in openFoam.

 tH3f0rC3 May 16, 2011 03:58

Quote:
 Originally Posted by akidess (Post 307737) Relaxation only applies to the SIMPLE algorithm, whereas most transient solvers in openFoam use PISO. A combination of both algorithms is called PIMPLE in openFoam.
Hi,
So can I set up the relaxationFactors in PIMPLE manually? Because you said PIMPLE is a combination of both algorithms.

Best Regards,
tH3f0rC3

 akidess May 16, 2011 04:27

Yes, you should be able to specify the relaxation parameters in all SIMPLE and PIMPLE based solvers.

 tH3f0rC3 May 16, 2011 04:32

Quote:
 Originally Posted by akidess (Post 307748) Yes, you should be able to specify the relaxation parameters in all SIMPLE and PIMPLE based solvers.
Hi,

do you know if this is simply done by typing the following into the fvSolution-file?
Code:

```relaxationFactors {   U  0.7;   p  0.8; ... }```
Best Regards,
tH3f0rC3

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