Convergence problem in a vertical vessel

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March 13, 2012, 19:23
Convergence problem in a vertical vessel
#1
Senior Member

Julio Mendez
Join Date: Apr 2009
Location: Greensboro, U.S.A
Posts: 254
Rep Power: 11
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.
Attached Images
 Sin título.jpg (93.1 KB, 13 views) Sin título 2.jpg (27.9 KB, 16 views)

 March 13, 2012, 23:32 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 13,881 Rep Power: 107 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 Senior Member   Julio Mendez Join Date: Apr 2009 Location: Greensboro, U.S.A Posts: 254 Rep Power: 11 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 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 13,881 Rep Power: 107 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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