# SIMPLE, SIMPLER or PISO?

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 October 16, 2007, 17:37 SIMPLE, SIMPLER or PISO? #1 Gem Leku Guest   Posts: n/a Hello How do you choose between the algorithms SIMPLE, SIMPLER or PISO? Are there any guideline somewhere? Can someone draft a recommendation? Thanks in advance G.L. ps: I noriced you can search for CFD users on http://www.linkedin.com

 October 18, 2007, 04:29 Re: SIMPLE, SIMPLER or PISO? #2 George Guest   Posts: n/a PISO is the more robust from the three algorithms. But it is a little bit more complex to implement. But in some cases the convergence is 20-50% faster. If I were you, I would choose PISO. It worth the extra trouble of incorporating the extra terms. SIMPLER on the other hand is a little bit faster than SIMPLE and it is extremely easy to implement. Just change a coefficient of the SIMPLE algorithm. hope it helps

 October 18, 2007, 23:44 Re: SIMPLE, SIMPLER or PISO? #3 billpeace Guest   Posts: n/a For compressible NS equation,which one are used?

 October 22, 2007, 04:59 Re: SIMPLE, SIMPLER or PISO? #4 George Guest   Posts: n/a I am sorry for a mistake in my previous message. In SIMPLEC there is only a change in a coefficient, while SIMPLER is a bit more complicated. All can be used for compressible flow.

 October 23, 2007, 23:27 Re: SIMPLE, SIMPLER or PISO? #5 billpeace Guest   Posts: n/a Are there any introduction on solving compressible flow by SIMPLE or other three algorithms? I know how to implement simple algorithm for incompressible flow,but add a energy equation for compressible flow. How to deal with the addition equation? thanks

 October 24, 2007, 04:50 Re: SIMPLE, SIMPLER or PISO? #6 George Guest   Posts: n/a You just compute density with the ideal gas law or any other law. And ofcourse the incoming flow rate does not equal the outcoming flow rate as in incompressible flows.

 October 24, 2007, 09:09 Re: SIMPLE, SIMPLER or PISO? #7 ag Guest   Posts: n/a Well, not quite. You do need to also solve the energy equation (typically the enthalpy equation is used.)

 October 24, 2007, 11:20 Re: SIMPLE, SIMPLER or PISO? #8 opaque Guest   Posts: n/a Dear George, Careful on: "And ofcourse the incoming flow rate does not equal the outcoming flow rate as in incompressible flows." Mass must be conserved. Therefore, for steady state calculations, the incoming mass flow must be identical to the outgoing mass flow. Int_over_allboundaries (density * velocity) dot dA = zero Opaque