|
[Sponsors] |
July 5, 2013, 03:41 |
steadyStatePisoFoam
|
#1 |
Senior Member
Dongyue Li
Join Date: Jun 2012
Location: Beijing, China
Posts: 838
Rep Power: 17 |
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?? Last edited by sharonyue; July 9, 2013 at 19:53. |
|
July 5, 2013, 07:51 |
|
#2 |
Senior Member
Mohsen KiaMansouri
Join Date: Jan 2010
Location: CFD Lab
Posts: 118
Rep Power: 16 |
Somebody please compare the SIMPLE, PISO and PIMPLE loops in a single flowchart.
I'm confused too
__________________
“If you have an apple and I have an apple and we exchange these apples then you and I will still each have one apple. But if you have an idea and I have an idea and we exchange these ideas, then each of us will have two ideas.” |
|
July 7, 2013, 19:58 |
|
#3 |
Senior Member
Dongyue Li
Join Date: Jun 2012
Location: Beijing, China
Posts: 838
Rep Power: 17 |
Still confused too
|
|
July 8, 2013, 05:48 |
|
#4 |
Senior Member
Dongyue Li
Join Date: Jun 2012
Location: Beijing, China
Posts: 838
Rep Power: 17 |
Looks like steadystate PISO is different with transient PISO. In this thread http://www.chemical-forum.com/thread-71382-1-1.html He said:
Code:
Hi, The original version of PISO was developed for transient calculation with small timesteps, so you have also small Courant numbers (<1) in this non-iterative variant. If you are running PISO like SIMPLE with outer Iterations you do not need small Courant numbers, but the convergence rate of PISO will then not be better or faster than SIMPLE! See also the paper "Solution of the implicitly discretised fluid flow euqations by operator splitting" by R.I. Issa! Good Luck! And, does it mean the momentum and continuity equations are simultaneously satisfied after the inner loops in PISO? |
|
July 9, 2013, 11:18 |
|
#5 |
Senior Member
Paulo Vatavuk
Join Date: Mar 2009
Location: Campinas, Brasil
Posts: 196
Rep Power: 17 |
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 Last edited by vatavuk; July 9, 2013 at 11:23. Reason: make it more clear |
|
July 9, 2013, 20:04 |
|
#6 | |
Senior Member
Dongyue Li
Join Date: Jun 2012
Location: Beijing, China
Posts: 838
Rep Power: 17 |
Quote:
|
||
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Influence of initial conditions in SteadyState | fshak92 | STAR-CCM+ | 2 | April 1, 2012 16:09 |
Switching from transient to steadystate : crash | alf12 | OpenFOAM Running, Solving & CFD | 0 | January 17, 2012 04:42 |
Problem with steadyState solvers using pressure BC | Victor | OpenFOAM | 1 | December 14, 2009 05:40 |
SteadyState | tutlhino | OpenFOAM Running, Solving & CFD | 5 | April 30, 2009 09:10 |
Pressure wave pattern over body in steadystate? | Chebeba | CFX | 1 | March 16, 2008 02:00 |