[Weiqiang Liu]

Hi all,
I am writing this thread to ask a really general question. That is how to deal with the divergence problem with Ansys Fluent.

The project I have been doing is the catalytic micro-channel combustion of methane.

Firstly, the version of fluent I used was fluent 15 and the gas and surface mechanisms I used were GRI 3.0 and DETCHEM respectively. I kept getting the error 'received fatal error: segmentation fault'. After some struggling, I found when I changed the gas mechanism to GRI 2.0, the error did not happen again.
By consulting to fluent staff, I knew it is because the old version of Fluent can not handle gas species more than 50 while GRI 3.0 has 53 species.

from the point on, I used Fluent 17.0 to continue my simulation. However, fluent keeps complaining about 'divergence detected in AMG solver: temperature'. Some measurements have been taken in attempting to solve this problem as follows:
1. decreasing the under relaxation factors. This is the most common method recommended in literature and forums.

2. turn off energy equation to get a 'cold flow' results and turn on energy equation to continue iteration.

3. make the leading edge of the catalytic wall inert. In other words, there is no surface reaction on the leading edge of the wall. Instead, a temperature boundary condition which has the same temperature with the inlet mixture is imposed.

4. using simpler gas mechanisms other than GRI 3.0

However, nothing above works. Fluent keeps telling me 'divergence detected in AMG solver'.

So I wrote email to those authors who have published papers of the same topic . Most of the authors used the in-house CFD code developed by their own group. They gave me suggestions just similar to those I mentioned above. Some other authors who used Fluent as well just told me to give a better initial guess in order to converge.

I am wondering is it really that hard for fluent to handle complex reaction schemes? Hope someone can give me some suggestions under this thread. or freshers like me can discuss this topic and share your experience.

Thanks very much!

weiqiang.