Linear solvers in OpenFOAM

blue_arrow98 · June 26, 2019, 04:49

Hey guys, I am doing a project on OpenFOAM simulating external flow over an airfoil. I am confused with various linear solvers available to solve the problem in the fvSoultion file.

Can anyone explain me the difference between GAMG and PCG solver for pressure and when is each one of them used?

Santiago · June 26, 2019, 12:34

Geometric Agglomerated MultiGrid

Parallel Conjugate Gradient

easy enough to look on the interwebs

akidess · June 27, 2019, 03:45

Quote:

Originally Posted by Santiago

Geometric Agglomerated MultiGrid

Parallel Conjugate Gradient

easy enough to look on the interwebs

AFAIK -> PCG = Preconditioned Conjugate Gradient.

Santiago · June 27, 2019, 04:11

Quote:

Originally Posted by akidess

AFAIK -> PCG = Preconditioned Conjugate Gradient.

I stand corrected

cryabroad · June 30, 2019, 06:22

Interesting topic! You can check out the following link to get some insights.

https://www.openfoam.com/documentati...e-solvers.html

Note there are GAMG preconditioners for PCG solvers, which is NOT the GAMG solver(belongs to the Multigrid solver catagory). By the way I remember some people stating that PCG solvers are better than GAMG for parallel computing. Is this true? What is the reason behind it?

akidess · July 2, 2019, 04:04

Quote:

Originally Posted by cryabroad

By the way I remember some people stating that PCG solvers are better than GAMG for parallel computing. Is this true? What is the reason behind it?

More grids means more communication overhead. Not that important for small parallel simulations, but can become important for massive sims.

cryabroad · July 2, 2019, 23:37

Thanks for the explanation!

Ruiyan

June 26, 2019, 04:49	Linear solvers in OpenFOAM	#1
blue_arrow98 New Member Rahul Join Date: Aug 2018 Posts: 6 Rep Power: 8	Hey guys, I am doing a project on OpenFOAM simulating external flow over an airfoil. I am confused with various linear solvers available to solve the problem in the fvSoultion file. Can anyone explain me the difference between GAMG and PCG solver for pressure and when is each one of them used?

June 30, 2019, 06:22		#5
cryabroad Senior Member Ruiyan Chen Join Date: Jul 2016 Location: Hangzhou, China Posts: 162 Rep Power: 10	Interesting topic! You can check out the following link to get some insights. https://www.openfoam.com/documentati...e-solvers.html Note there are GAMG preconditioners for PCG solvers, which is NOT the GAMG solver(belongs to the Multigrid solver catagory). By the way I remember some people stating that PCG solvers are better than GAMG for parallel computing. Is this true? What is the reason behind it? blue_arrow98 likes this.

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June 26, 2019, 12:34		#2
Santiago Senior Member Santiago Lopez Castano Join Date: Nov 2012 Posts: 354 Rep Power: 15	Geometric Agglomerated MultiGrid Parallel Conjugate Gradient easy enough to look on the interwebs

July 2, 2019, 23:37		#7
cryabroad Senior Member Ruiyan Chen Join Date: Jul 2016 Location: Hangzhou, China Posts: 162 Rep Power: 10	Thanks for the explanation! Ruiyan