steadyStatePisoFoam
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Hi,
In SIMPLE and steadystate PISO, There are a little differences, and I made a picture to show this by my comprehension. What I am courious about is why there are some correctors loops in PISO, in my image, if I get u** v** p**, it has been divergence free, But if omit this correctors loop, PISO would become SIMPLE .... So whats the meaning of this correctors loop in steadystate PISO? Just now I compiled a steadyStatePisoFoam, use this solver solving cavity it use 317 iterations compared with simpleFoam's 47's iterations. So now I am more confused about this inner loop, can it really speed up the solving process? And in Versteeg's book page 196, he said:"As before, under-relaxation is required with the procedure in PISO" , AFAIK, in openFoam PISO dont need relaxation. so?? |
Somebody please compare the SIMPLE, PISO and PIMPLE loops in a single flowchart.
I'm confused too :confused::confused::confused: |
Still confused too
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Looks like steadystate PISO is different with transient PISO. In this thread http://www.chemical-forum.com/thread-71382-1-1.html He said:
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Hi, And, does it mean the momentum and continuity equations are simultaneously satisfied after the inner loops in PISO? |
Hi Forrest,
In OpenFOAM there is no PISO algorithm for steady-state simulation, only for transient flow simulations. You can use it to solve a steady state problem if you let the simulation continue for such a long time that the transient behavior disappears, but there are some flows that never reach this condition, like the flow around a cylinder that has vortex shedding behavior. For a real steady flow simulation you can use SIMPLE. The PISO algorithm has a limitation that the time step must be small otherwise it will diverge so, to overcome this limitation the PIMPLE algorithm was developed, it is a combination of the two algorithms. Best Regards, Paulo |
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