residuals and results oscillating during some iteration interval
 

Hi all,

I am simulating a propane catalytic combustion with user-defined one step gas phase and surface reaction with fluent. it's a steady state case. after iteration started, temperature just proceeded to goal value normally. When it was close to goal temperature, all residuals suddenly started to oscillate and so did the temperature results. If I decrease URF of energy, the oscillation would be postponed after tens thousand of iterations. However, it still occured.

I tried to turn off surface reaction with gas phase reaction only since I am pretty sure about the correctness of gas phase reaction. Then the case can be converged very well. I defined the surface reaction following literature. Because there is no nomenclature in the paper. I can't know the units in those equations. I just did some unit transformation.

I am wondering why would this happen. Is something wrong with my surface reaction scheme?

Ps: I am using non-explicit source chemistry solver. If I use stiff chemistry solver, oscillation would occur along the whole iteration process.

Best regards

Weiqiang

How you found the solution of your problem? I have the same issue.