# Multiphase PISO loop in OpenFoam

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 June 9, 2011, 16:04 Multiphase PISO loop in OpenFoam #1 Senior Member   CFDtoy Join Date: Mar 2009 Location: United States Posts: 145 Blog Entries: 2 Rep Power: 17 Hello Foamers, I have a question on the PISO implementation in OF - particularly for multiphase applications. For PISO solutions, for example, the loop taken from twoPhaseEulerFoam or multiphaseInterFoam reads, for (int corr=0; corr

 June 10, 2011, 04:50 #2 Senior Member   Laurence R. McGlashan Join Date: Mar 2009 Posts: 370 Rep Power: 23 I think the additional correction for alpha is there to speed up convergence? I've never used it myself. I don't have a reference for it but you can start from the theses (especially Hill's which discusses the multiphase PISO algorithm) from Imperial which are all here: http://www.foamcfd.org/ __________________ Laurence R. McGlashan :: Website

 June 10, 2011, 05:02 #3 Senior Member     Anton Kidess Join Date: May 2009 Location: Germany Posts: 1,377 Rep Power: 30 I think the reason for just updating the VF equation once per time step is that per default, OF uses MULES::explicit. Due to that, you are restricted to a fairly small time step, and you can assume the system converged with one iteration. Wrapping all three equations in a loop might be helpful to enable larger time steps with MULES::implicit.

June 10, 2011, 09:51
MP Piso loop
#4
Senior Member

CFDtoy
Join Date: Mar 2009
Location: United States
Posts: 145
Blog Entries: 2
Rep Power: 17
Thanks for your quick response. Basically for MP the solution procedure typically requires

solve vf
solve U
Solve P'
Correct U, P

This is simple schema.

For MP PISO,

solve vf
solve U
solve P'
Correct U, P (correct vf?)
solve U
solve P'

Hence, according to PISO extended from single phase, we do need correction for vf after solving P eqn first isnt it?

This is basically arising from the fact that if it was a single phase case, rho would have to be corrected after solve P' everytime.

So, is this still a PISO procedure ?!?? I am not sure. This implemented procedure is modified PISO probably ..but then what is the basis?

I have Hill's work and other Foam theses - which indicates similar implementation - PISO-2P procedure. With vf fractions corrected at the end.

All these OF solvers for cavitation, interFoam, mixingFoam have different implementation and not consistent. If convergence is the main issue, this should be suggested.

Feedback on this is greatly appreciated !

Thanks,

CFDtoy

Quote:
 Originally Posted by akidess I think the reason for just updating the VF equation once per time step is that per default, OF uses MULES::explicit. Due to that, you are restricted to a fairly small time step, and you can assume the system converged with one iteration. Wrapping all three equations in a loop might be helpful to enable larger time steps with MULES::implicit.
__________________
CFDtoy

 Tags multiphase, openfoam 1.6, piso