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icoFoam vs. pimpleFoam

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Old   May 21, 2013, 06:15
Default icoFoam vs. pimpleFoam
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Tobias Holzmann
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Hi all,

I am working with OF for 3 years now and sometimes I get very interessting results or Problems.

I set up a very simple case:

- a pipe (Diameter 10cm and length 50cm)
- inside is a sphere with diamater 2cm


The Setup is: laminar flow with 0.05m/s


The interesting thing is:

- icoFoam is running without a Problem
- pimpleFoam decrease the timestep after t=0.0015s to 10^-10 and so on

I analysed the flow after that time and saw that I get big velocity and pressure gradients at the outlet. Otherwise icoFoam solves the case without a Problem - same bc and Setup.


Does someone knows why the differences appears between the solvers (pressure equation?)?

In my opinion it should be possible to solve that simple case with the pimple algorithm too, isnīt it?


It would be nice if there is a discussion on that effect.


Thanks in advance and for the help.
Tobi
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Old   May 21, 2013, 08:16
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Daniel Pielmeier
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It is probably a good idea to post your fvSolution files for both solvers. I guess you use the same numbers for pressure correction. How many outer correctors do you use for pimpleFoam and is the momentumPredictor turned on.

I also had problems with a decreasing time step using the pimple algorithm. Using the momentumPredictor as well as increasing nOuterCorrectors and nCorrectors did help a lot in that situation.
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Old   May 21, 2013, 09:21
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Hi Billie,

I used limitedLinear schemes in both solvers.

I am at work at the Moment but later I ll have a look at the Settings in the fvSolution file.

I ll update you (all) today evening.

Thanks for the first advice
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Old   May 21, 2013, 10:34
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From a quick glance at the code for both solvers I understand it as the following. Using pimpleFoam (PIMPLE-loop) with nOuterCorrectors=0, momentumPredictor=on and the same values for nCorrectors like in icoFoam (PISO-loop) should be the same as using plain icoFoam. Correct me if I am wrong.
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