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Warning: Surface chemistry solver did not converge

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Old   February 27, 2013, 15:15
Default Warning: Surface chemistry solver did not converge
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Parisa
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Hello guys,
I am simulating a surface reaction in FLUENT, finite-rate.
When the iteration stats, the following error shows up:

Warning: Surface chemistry solver did not converge for 203 cells/faces


I reduced the density under-relaxation. Also, I simulated the flow alone to stabilize the flow and after that started to solve surface chemistry, but the above error happened again.
Can anyone kindly help me to resolve this issue?
Thanks,
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Old   March 12, 2014, 12:58
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şakir
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I have same problem. Is there any answer?
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Old   April 1, 2014, 15:32
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John
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I think, very stiff surface reaction mechanism.
There is always this problem with Mr. Deutschmann's mechanisms for me...
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Old   April 30, 2014, 08:03
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Kostis Chatzi
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i have the same message-warning.i have imported the deutschmann's mechanism for methane combustion with 24 surface reactions. does this warning affect my results and their validity ?
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Old   May 2, 2014, 09:09
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Surely, it does. You should have high residuals that don't decrease in that case. There are some steps to try:
1) Try to use under-relaxation factors (I usually choose these about 0.7-0.8) for unconverging species and energy equation.
2) After some iterations with URFs you can gradually increase URFs to their initial values (sometimes you can't do this - then stop at max. URFs for that the solution converges).
3) Do more iterations - does the number of unconverged cells reduce?
4) If it doesn't help, try to change advanced solver options.
I usually use 1-3 steps.
I think, URFs are useful for stiff systems - when we need to use small step for some variables (equations) in iterative methods. It can help to reach the stable steady-state solution (we assume that it exists following by the authors - but it's not necessarily the case).
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Old   May 3, 2014, 11:50
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thank you for your assistance, villager
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