Warning: Surface chemistry solver did not converge

Parisa_Khiabani · February 27, 2013, 15:15

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,

silverra1n · March 12, 2014, 12:58

I have same problem. Is there any answer?

villager · April 1, 2014, 16:32

I think, very stiff surface reaction mechanism.
There is always this problem with Mr. Deutschmann's mechanisms for me...

kostis217 · April 30, 2014, 09:03

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 ?

villager · May 2, 2014, 10:09

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).

kostis217 · May 3, 2014, 12:50

thank you for your assistance, villager

February 27, 2013, 15:15	Warning: Surface chemistry solver did not converge	#1
Parisa_Khiabani Member Parisa Join Date: Feb 2013 Posts: 51 Rep Power: 13	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,

April 1, 2014, 16:32		#3
villager Member vlg Join Date: Jul 2011 Location: My home :) Posts: 81 Rep Power: 18	I think, very stiff surface reaction mechanism. There is always this problem with Mr. Deutschmann's mechanisms for me... silverra1n likes this.

May 2, 2014, 10:09	Maybe 'll help	#5
villager Member vlg Join Date: Jul 2011 Location: My home :) Posts: 81 Rep Power: 18	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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March 12, 2014, 12:58		#2
silverra1n Member şakir Join Date: Mar 2012 Posts: 30 Rep Power: 14	I have same problem. Is there any answer?

April 30, 2014, 09:03		#4
kostis217 New Member Kostis Chatzi Join Date: Apr 2014 Location: Greece Posts: 20 Rep Power: 12	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 ?

May 3, 2014, 12:50		#6
kostis217 New Member Kostis Chatzi Join Date: Apr 2014 Location: Greece Posts: 20 Rep Power: 12	thank you for your assistance, villager