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Old   April 19, 2016, 12:34
Default PIMPLE algorithm
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Sheikh Ahmed
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Could anyone please describe the PIMPLE algorithm in OpenFOAM in a little more details; what equations it solves, in which sequence etc. I saw in one of the cases the following description-

PIMPLE
{
momentumPredictor no;
nOuterCorrectors 1;
nCorrectors 2;
nNonOrthogonalCorrectors 0;
}
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Old   April 27, 2016, 07:37
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Saideep
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hi,

1. Basically PIMPLE is a semi- implicit method for pressure - velocity coupling.
2. From my understanding the velocity term is solved explicit and pressure term implicit.
3. Basically the idea is to solve NSE.

Look at UEqn.H
1. Solves for LHS part of NSE.

2. The second part is a "momentum predictor" step which tries to predict the velocity explicitly based on previous pressure time step values for present time step.
Note that the compiler goes through this portion only when you use momentum predictor "yes". Else you still have the velocity computed through previous time step source/ sink terms.

Look at pEqn.H
Now you split the velocity matrix into diaognal and off diagonal components.
Look at thread named "meaning of HbyA" in cfdonline(OpenFOAM).
Now wrt your body/ surface forces you develop a new matrix implicitly for pressure.

By doing so you are not any more mass conservative but you can determine actual pressure. With this pressure value, we can compute mass conservative fluxes and update velocities.

So, the "nOuterCorr" value represents number of times you loop over entire pimple loop {for example: interFOAM solver solves for alphaEqn, Ueqn, pEqn}, whereas "nCorr" represents number of times loop for pressure correction to obtain mass conservative fluxes.
In short:
nOuterCorr : loops through all NSE variables.
nCorr: loops only through pEqn.

For more details: look at Tobi blog.

If anyone comes across this I really dont understand what "ddtCorr" function does. Any ideas over that?

Saideep
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Old   April 27, 2016, 10:42
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Sheikh Ahmed
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Thank Saideep. I am sorry I dont about ddtCorr. Anyone has any idea of it?
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Old   May 1, 2016, 16:26
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Bruno Santos
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Quick answer: http://openfoamwiki.net/index.php/Op...hm_in_OpenFOAM
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