[n.makhtoomi]

hi
someone could explain me the process behind PIMPLE. Up to now my knowledge about this is this:
* PIMPLE is a hybrid of SIMPLE/PISO
* It's pseudo-transient
questions:
Which properties of PISO/SIMPLE are merged into PIMPLE?
What exactly is the gain from using PIMPLE?
Does PIMPLE switch from PISO to SIMPLE at a specific point? Maybe during the transient period it's using pressure correction basend on PISO and when the flow gets steady it switches to SIMPLE. Does that make sense?
thanks.

[Bernhard]

You can find a lot of information on this forum about this topic, see, e.g. http://www.cfd-online.com/Forums/ope...s-icofoam.html

What pimpleFoam does, is just looping over the PISO algorithm within one time step. This allow for some under-relaxation between these loops, what you don't do with pisoFoam. As far as I know the reasoning behind is the possibility for larger time-step and stability. The pimple algorithm easily reduces to pure PISO by using one outer loop. It will not switch to simple, because it is a unsteady solver. It will not switch to simple in a smart way. Be sure to compare the source codes of the solvers. It will clearly show how these loops are structured.

[n.makhtoomi]

Originally Posted by Bernhard

You can find a lot of information on this forum about this topic, see, e.g. http://www.cfd-online.com/Forums/ope...s-icofoam.html

....

I read that link
I knew that
pimpleFoam is large time-step transient solver for incompressible flow using the PIMPLE(merged PISO-SIMPLE) algorithm
pimple Algorithm is more robust and efficient
Pimple offers you more control by providing nOuterIterations parameter. Where as if nOuterIterations is = 1, you pimple is just simply a piso Algorithm
So definitely some addition cost on computation with more outer iterations could improve your results
PIMPLE permits the use of the entry adjustTimeStep yes in the controlDict
maxCo=10 ! And it is still stable and realist and of course much faster
Pimple being an Implicit numerical method, you can use a large Co, greater than 1

[n.makhtoomi]

I would like to know
How does PIMPLE-algorithm work?
Which properties of PISO/SIMPLE are merged into PIMPLE?
What exactly is the gain from using PIMPLE?
Does PIMPLE switch from PISO to SIMPLE at a specific point?
I want to do with buoyantBoussinesqPimpleFoam
Really appreciating your answers
regards,
n.makhtoomi

[ni-openfoam-user]

Hi,

Just wondering if you ever found an answer to your question?

Kind regards,

James

[RodriguezFatz]

In OpenFoam simpleFoam is a steady-state solver, pimpleFoam and pisoFoam are for transient problems.
PisoFoam solves the momentum equation once each time-step and afterwards does the correction to satisfy continuity.
PimpleFoam also solves the momentum equation, then does the pressure correction. Now it keeps in the same time-step and iteratively enhances the result by solving the momentum equation again. This is done as often as you want each time-step. Thus, if you set the number of outer correctors in PimpleFoam to "1" you will get the pisoFoam algorithm.