I am using FLUENT to simulate coal combustion in a pilot furnace, where swirl flow occurs. As simulating, I never got a convergence as coal combustion included. Is there somebody having experience to solve such a problem?

I have never met theoretically perfect convergence for the coal combustion with DPM. Gas phase convergence can be obtained fairly easily, but the residuals always increases to the fairly higher values than the convergence criterion just after DPM injection.

So, my personal convergence criterion is,

1) Enough DPM injection, say N(fairly large number) times injection and coupling with gas phase. 2) Gas phase convergence. 3) perfect mass&energy balance including mass and energy transfer between two phases. 4) Nearly same results between N_th converged result and N+1_the converged result for every variables

Oil droplet combustion is fairly easily converged. So, I think that the major source of difficult convergence for coal combustion is large momentum transfer between two phases rather than energy transfer. So, I think that the problem can be overcomed by using very large cell number and very large injection number. I actually have tested couple of times by incresaing and decreasing injection number. For large injection number, the situation was much better.

Sincerely, Jinwook