# question to courant criterion

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 May 12, 2011, 02:16 question to courant criterion #1 Senior Member   Join Date: Mar 2011 Posts: 155 Rep Power: 7 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

 May 12, 2011, 07:08 #2 Senior Member   Join Date: Mar 2011 Posts: 155 Rep Power: 7 I have just recognized that it is possible to set the time step also to delta t = 0.1 Best Regards, tH3f0rC3

 May 16, 2011, 02:22 #3 Senior Member   Join Date: Mar 2011 Posts: 155 Rep Power: 7 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

 May 16, 2011, 03:27 #4 Senior Member     Anton Kidess Join Date: May 2009 Location: Delft, Netherlands Posts: 1,142 Rep Power: 20 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.

May 16, 2011, 03:58
#5
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Quote:
 Originally Posted by akidess 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

 May 16, 2011, 04:27 #6 Senior Member     Anton Kidess Join Date: May 2009 Location: Delft, Netherlands Posts: 1,142 Rep Power: 20 Yes, you should be able to specify the relaxation parameters in all SIMPLE and PIMPLE based solvers.

May 16, 2011, 04:32
#7
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Join Date: Mar 2011
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Quote:
 Originally Posted by akidess 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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