Convergence problems with non-premixed combustion in a small hydrogen/oxygen rocket engine
I'm trying to simulate a non-premixed combustion with gaseous hydrogen and oxygen. I'm only interested in the combustion and mixing of the gases, so my outlet is set to the throat (I thought this would make the case more simple sincethe flow is subsonic only) . As boundary conditions I choosed mass flow inlets (mass flow is fixed) and pressure outlet.
My problem is that I'm not able to get a converged solution, my outlet mass-fraction of h2o is highly oscillating as well as the outlet mass-flow.
For outlet I calculated the pressure with CEA (a program from NASA for rocket engine performance calculations). I'm still confused how to set operating pressure and gauge pressure... I tried to use 0 operating pressure and the calculated value as gauge pressure and also the other way. I also tried to use the average pressure in the flow field as operating pressure.
Maybe you can give me some advice on how to get a reasonable solution.
Relizeable k-e, energy eqn on, non-premixed, chemical equilibrium, coupled, second order, default and reduced relaxation factors
Thank you very much