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-   -   PISO vs. SIMPLE (http://www.cfd-online.com/Forums/main/9007-piso-vs-simple.html)

benedikt flurl April 12, 2005 08:27

PISO vs. SIMPLE
 
Im testing at the moment my new implemented PISO routine, and I can not find any advantages compared with SIMPLE. I am testing with the Karman Vortex Street. In PISO and in SIMPLE it is no Problem to set the underrelaxation factors for pressure correction to 1 (underrelaxation for u,v 0.5). And SIMPLE converges as rapidly as PISO. Has anybody from you good experience with the PISO algorithm and can anybody tell me, when I can justify running PISO without iteration (for this reason it was developed I think?!). Thank you very much for your help!

Benedikt.

PS: Is the Karman Vortex street a bad testcase for comparing PISO with SIMPLE? PPS: I can let run PISO and SIMPLE without iterations an get not bad results (compared with eperimental data)

pkm April 13, 2005 06:03

Re: PISO vs. SIMPLE
 
i remember having seen a paper (~1998? i don't recall any details - can anyone help?) where it was claimed that for a flow situation with negative pressure gradient, approaching stagnation followed by separation, PISO scores highly over SIMPLE.

George April 14, 2005 06:54

Re: PISO vs. SIMPLE
 
Hi! I think there are some versions of PISO.Some of them are as fast (or as slow) as SIMPLE,but some others are amazing how quickly they converge.I think the difference among them is how many assumptions they make. Does your code is for compressible or incompressible flow? I am not sure, but I think this can play some role on the convergence.


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