# Algebraic Multigrid for CFX Transient Analysis

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 April 29, 2013, 11:14 Algebraic Multigrid for CFX Transient Analysis #1 New Member   Join Date: Apr 2013 Posts: 5 Rep Power: 6 Hi ! I am studying a transient thermal problem using CFX. The solution seems to converge. But I would like to try to apply multigrid technique in order to accelerate the solution process. I am a bit confused with the solver control parameters. Could someone explain me please (or give a hint) where can I find parameters that control the application of Multigrid method. (I have looked into CFX Solver Modeling Guide, p. 450, 16.3.2 Linear Solver Parameters but I can not figure out how to use multigrid...) Thank you in advance !

 April 29, 2013, 11:29 #2 Senior Member   Lance Join Date: Mar 2009 Posts: 619 Rep Power: 15 CFX already use algebraic multigrid, and Im not sure that fiddeling with the parameters will speed up your simulation. If you check the expert parameters you will find that multigrid solver = true (by default) and that mg solver option = 5 (automatic)

 April 29, 2013, 19:04 #3 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,077 Rep Power: 109 This sort of comment seems to be a relic of SIMPLE based solvers where you continually had to tweak the under relaxation factor to get good convergence, and you also had to keep an eye on the linear solvers as well. With modern solvers like CFX it is very rare that you have to do this. These days 99% of the time the convergence issue is caused by a fundamental problem with the simulation setup and nothing to do with details of the linear solver.

 April 30, 2013, 09:36 #4 Senior Member   OJ Join Date: Apr 2012 Location: United Kindom Posts: 475 Rep Power: 13 FLUENT has a coupled solver as well, though it uses the SIMPLE based solver as a default one. I wonder if anyone has done any comparison between these two coupled solvers! OJ

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