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Old   August 21, 2013, 10:52
Default Simple vs piso
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Dongyue Li
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Hi guys,

Im working on the reseach regarding the difference between steady SIMPLE and steady PISO. Its tough to write in this forum. So see the image pls.

My reference is H K Versteeg's book: An introduction to .......

As we know, in PISO we have a second corrector step which make it different with SIMPLE, but my confusion is why is this second corrector step instrumental to the solving?

In H Ks book, I make a conclusion(IF I WAS WRONG, CORRECT ME PLEASE):
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File Type: jpg SIMPLE.jpg (57.2 KB, 29 views)
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Old   August 21, 2013, 11:25
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The corrective pressure computed from the SIMPLE method is not the real pressure, so the second step is to make sure divergence of the corrected velocity field is zero. That is why the projection method is more popular than the SIMPLE method in the computation of unsteady flows.
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Old   August 21, 2013, 20:05
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Quote:
Originally Posted by hilllike View Post
The corrective pressure computed from the SIMPLE method is not the real pressure, so the second step is to make sure divergence of the corrected velocity field is zero. That is why the projection method is more popular than the SIMPLE method in the computation of unsteady flows.
Hi Xingyue

Quote:
Originally Posted by hilllike View Post
The corrective pressure computed from the SIMPLE method is not the real pressure,
AFAIS, the corrective pressure computed from PISO is not the real pressure either. but which I think is divergence free.

Am I right?

So, as you had said, both of the first step in SIMPLE and the two steps in PISO are making sure the velocity field divergence free, Why does PISO make it divergence free twice?

If I was wrong above, correct me, Thanks in advance.
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Old   August 21, 2013, 21:42
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This will make it clearer.
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Old   August 22, 2013, 03:22
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Quote:
Originally Posted by sharonyue View Post
Hi Xingyue


AFAIS, the corrective pressure computed from PISO is not the real pressure either. but which I think is divergence free.

Am I right?

So, as you had said, both of the first step in SIMPLE and the two steps in PISO are making sure the velocity field divergence free, Why does PISO make it divergence free twice?

If I was wrong above, correct me, Thanks in advance.
What I said is based on my understanding and I haven't written a code of PISO.

In SIMPLE method, the approximated velocity is computed implicitly but the corrective pressure is computed explicitly. That can't be coupled with one iterative step.
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