# PIMPLE algorithm

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 April 19, 2016, 12:34 PIMPLE algorithm #1 Member   Sheikh Ahmed Join Date: Dec 2015 Location: South Carolina, USA Posts: 88 Rep Power: 8 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; }

 April 27, 2016, 07:37 #2 Senior Member   Saideep Join Date: Apr 2015 Location: INDIA Posts: 203 Rep Power: 10 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 massive_turbulence, AshwaniAssam, utkunun and 2 others like this.

 April 27, 2016, 10:42 #3 Member   Sheikh Ahmed Join Date: Dec 2015 Location: South Carolina, USA Posts: 88 Rep Power: 8 Thank Saideep. I am sorry I dont about ddtCorr. Anyone has any idea of it?

 May 1, 2016, 16:26 #4 Retired Super Moderator   Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 10,965 Blog Entries: 45 Rep Power: 126

 March 20, 2019, 22:10 #5 Senior Member   Brett Join Date: May 2013 Posts: 197 Rep Power: 11 What does PIMPLE stand for?

 March 21, 2019, 01:19 #6 Member   Andreas P. Join Date: May 2017 Posts: 41 Rep Power: 7 I think it is just the combination of the two acronyms PISO and SIMPLE, while PISO stands for Pressure-Implicit with Splitting of Operators ans SIMPLE stands for Semi-Implicit Method for Pressure Linked Equations.

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