[Habibfateh]

Hello my friends
I have a cement rotary kiln for modeling in openfoam.
at first I want to model combustion of this kiln. so I use "reacting foam solver" for this purpose.
A summarize of problem:
- Cement rotary kiln combustion (length=67 m/diameter=4 m)
- one Fuel nozzle/ diameter=0.06 m/ velocity=140 m/sec
- primary air nozzle/ diameter=0.013 m/ velocity=50 m/sec
- secondary air / diameter=1.75 m/ velocity=1 m/sec
I model this kiln but in the process of solution in reactingfoam I see a fluctuate treatment for velocity vectors and pressure. at the time we have correct flow and at a little time (0.05 sec) before or after we have reverse flow(flow is come back) even at long time such as 10 sec , 15 sec and 20 sec.

Is it from pressure boundary condition? or from other boundary conditions? or from anything else?
I calculate every parameter in the solver and test different turbulent models but there isn't any change in solution.
please help.
How can I do now?
also consider that my solution time is long.