Convergence problem in a vertical vessel

juliom · March 13, 2012, 19:23

Dear colleagues, I am having a weird problem in CFX, the main problem is a vertical separator, but if I model it with a symmetry plane it converges.
In the other hand if I model it without a symetry, the convergence problem starts. Attached you will find the residual and the model pictures
The separator has one inlet and two outlets, here I explain the boundaries conditions:
Inlet : flow mass 15 lb/seg
Top outlet: Average static pressure (0 psi)
Bottom outlet: Average static pressure (0.52 psi).

The fluid is gas with constant propierties, K-E for turbulence.
High resolution for Advection scheme and auto timescale.
As yuou can see the case is very simple and I don´t know what is happening.

ghorrocks · March 13, 2012, 23:32

This is almost certainly caused by a transient flow starting up, which the symmetry plane prevented. See the FAQ for further details: http://www.cfd-online.com/Wiki/Ansys...gence_criteria

juliom · March 14, 2012, 08:36

Dear Glenn,
Could you explain a little bit more, because I´ve read this FAQ several time and I don´t find anything new to get convergence in my case.
Thanks before hand

ghorrocks · March 14, 2012, 17:21

The FAQ seems clear to me. I would remove the symmetry plane, and try a larger time step. If that does not give convergence then your flow is not steady state and you have to run transient.

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March 13, 2012, 23:32		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	This is almost certainly caused by a transient flow starting up, which the symmetry plane prevented. See the FAQ for further details: http://www.cfd-online.com/Wiki/Ansys...gence_criteria

March 14, 2012, 08:36		#3
juliom Senior Member Julio Mendez Join Date: Apr 2009 Location: Fairburn, GA. USA Posts: 290 Rep Power: 18	Dear Glenn, Could you explain a little bit more, because I´ve read this FAQ several time and I don´t find anything new to get convergence in my case. Thanks before hand

March 14, 2012, 17:21		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	The FAQ seems clear to me. I would remove the symmetry plane, and try a larger time step. If that does not give convergence then your flow is not steady state and you have to run transient.