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Convergence issue with continuity equation

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Old   June 11, 2005, 20:53
Default Convergence issue with continuity equation
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Jake
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Hi,

I am modeling flow in a microchannel and is experiencing convergence issue with the continuity equation. I tried using a lower under-relaxation factor for the momentum and this does help sometimes but not always. Is there anything that I could do to aid/assist the convergence?

Thanks in advance.
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Old   June 11, 2005, 21:36
Default Re: Convergence issue with continuity equation
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hx
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Hi. I meet the same problem with yours before. I regenerate grid from Gambit to solve the problem. By the way, I find that sometimes increases some under-relaxation factors can improve the convergence. I want also to get some advice about this problem.
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Old   June 14, 2005, 10:35
Default Re: Convergence issue with continuity equation
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John
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Check mass flux in "report flux" to see whether it is convergent or not
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Old   June 14, 2005, 10:50
Default Re: Convergence issue with continuity equation
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Jake
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Yes, the mass flux is convergent. I switched to SIMPLEC for the pressure-velocity coupling and used a higher (0.7) under-relaxation factor for pressure and a lower value (0.3) for momentum. Seems to work out pretty well initially. But when I switched to a finer mesh, all the residuals start being unstable (oscillate). Any advice will be appreciated.

Thanks.
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Old   June 14, 2005, 22:21
Default Re: Convergence issue with continuity equation
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John
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Advice: 1 the mesh quality 2 the discretization scheme 3 try to use the coupled solver 4 contact FLUENT for help Good luck
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Old   June 15, 2005, 13:05
Default Re: Convergence issue with continuity equation
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Riaan
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Agree with John

1) Continuity problems normally come from bad meshing - e.g. adjacent cells spacing differs a lot 2) Check your pressure contour plots to see if there are any sharp discontinuities in the lines 3) Run double point precision

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Old   June 15, 2005, 16:14
Default Re: Convergence issue with continuity equation
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Jake
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Not sure if this could causing the continuity problem - I am using non-conformal meshing...
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