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-   -   Convergence issue with continuity equation (http://www.cfd-online.com/Forums/fluent/36924-convergence-issue-continuity-equation.html)

Jake June 11, 2005 20:53

Convergence issue with continuity equation
 
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.

hx June 11, 2005 21:36

Re: Convergence issue with continuity equation
 
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.

John June 14, 2005 10:35

Re: Convergence issue with continuity equation
 
Check mass flux in "report flux" to see whether it is convergent or not

Jake June 14, 2005 10:50

Re: Convergence issue with continuity equation
 
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.

John June 14, 2005 22:21

Re: Convergence issue with continuity equation
 
Advice: 1 the mesh quality 2 the discretization scheme 3 try to use the coupled solver 4 contact FLUENT for help Good luck

Riaan June 15, 2005 13:05

Re: Convergence issue with continuity equation
 
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


Jake June 15, 2005 16:14

Re: Convergence issue with continuity equation
 
Not sure if this could causing the continuity problem - I am using non-conformal meshing...


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