Under-relaxation of PISO

gregor.vidmar153 · August 27, 2010, 11:07

I'm interested in what actually does UEqn.relax() in pisoFoam ?
It stabilized (accelerated) my comptutation of the thermo flow in a channel and the phase change liquid-solid a lot, but I do not know if the solution is correct, I mean the transient solution, not the steady-state one.

Thanks for any help,

Gregor

sharonyue · September 3, 2013, 03:57

UEqn.relax() exists in pisoFoam. but there is no p.relax(), Im confused too. Did you find a solution?

gregor.vidmar153 · September 3, 2013, 04:09

Not yet, unfortunately.

With regards.

G.

Houthuys · June 9, 2017, 05:16

It's an old thread but I also can't find an answer.

Do any one know why we have Ueqn,relax() in pisoFoam which is a transient solver ?

Also when we should use equation relaxation (Ueqn.relax()) and explicit relaxation (p.relax)?

Any contribution is highly appreciated

sharonyue · June 9, 2017, 05:55

No matter SIMPLE, PISO, SIMPLEC or others, you can UEqn.relax(). However, you can not p.relax() for PISO. But p.relax() works for SIMPLE and SIMPLEC.

See Peric page 177.

August 27, 2010, 11:07	Under-relaxation of PISO	#1
gregor.vidmar153 New Member Gregor Join Date: Jan 2010 Location: Ljubljana, Slovenia Posts: 5 Rep Power: 16	I'm interested in what actually does UEqn.relax() in pisoFoam ? It stabilized (accelerated) my comptutation of the thermo flow in a channel and the phase change liquid-solid a lot, but I do not know if the solution is correct, I mean the transient solution, not the steady-state one. Thanks for any help, Gregor

June 9, 2017, 05:55		#5
sharonyue Senior Member Dongyue Li Join Date: Jun 2012 Location: Beijing, China Posts: 849 Rep Power: 18	No matter SIMPLE, PISO, SIMPLEC or others, you can UEqn.relax(). However, you can not p.relax() for PISO. But p.relax() works for SIMPLE and SIMPLEC. See Peric page 177. __________________ My OpenFOAM algorithm website: http://dyfluid.com By far the largest Chinese CFD-based forum: http://www.cfd-china.com/category/6/openfoam We provide lots of clusters to Chinese customers, and we are considering to do business overseas: http://dyfluid.com/DMCmodel.html

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September 3, 2013, 03:57		#2
sharonyue Senior Member Dongyue Li Join Date: Jun 2012 Location: Beijing, China Posts: 849 Rep Power: 18	UEqn.relax() exists in pisoFoam. but there is no p.relax(), Im confused too. Did you find a solution?

September 3, 2013, 04:09		#3
gregor.vidmar153 New Member Gregor Join Date: Jan 2010 Location: Ljubljana, Slovenia Posts: 5 Rep Power: 16	Not yet, unfortunately. With regards. G.

June 9, 2017, 05:16		#4
Houthuys New Member rik houthuys Join Date: Jan 2017 Posts: 27 Rep Power: 9	It's an old thread but I also can't find an answer. Do any one know why we have Ueqn,relax() in pisoFoam which is a transient solver ? Also when we should use equation relaxation (Ueqn.relax()) and explicit relaxation (p.relax)? Any contribution is highly appreciated