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Convergence problem in a vertical vessel

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Old   March 13, 2012, 19:23
Default Convergence problem in a vertical vessel
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Julio Mendez
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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
File Type: jpg Sin título.jpg (93.1 KB, 13 views)
File Type: jpg Sin título 2.jpg (27.9 KB, 16 views)
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Old   March 13, 2012, 23:32
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Glenn Horrocks
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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
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Old   March 14, 2012, 08:36
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Julio Mendez
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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
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Old   March 14, 2012, 17:21
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Glenn Horrocks
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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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