Hello dear CFD modellers,

I have been playing around with FLUENT for some time now and have finally hit a few brick walls.

Firstly, I am trying to model a combustor with 2 H2 inlets and an O2 inlet. A Laval nozzle is at the end of the chamber which is set as a pressure outlet. The model is 2D axisymmetric with a relatively coarse mesh.

I have used Prepdf to calculate the mixture properties and it has been implemented into fluent. I require relatively high inlet velocities and therefore I have been increasing inlet velocities incrementally to avoid divergence.

Now, the residuals are good but the solution is not. The pressure inside the chamber does not increase with increasing propellant mass flux. The only way I can increase the internal chamber pressure is by increasing the outlet pressure.

So, if I set pressure outlet to 50 bar, the chamber is also 50 bar. Then, with an O2 injection temperature of 120K at and 50 bar, the density of O2 in the inlet (before combustion) is no-where near where it should be....(ie its about 20kg/m³ when it should be ~900kg/m³)

Is there a better was to model this? I also tried incompress. ideal gas approach with an H2/air mixture template. I thought about doing this and applying a temperature patch ...would this work perhaps?

Any help is greatly appreciated. Jouch

Why don't you adapt your grid according to chosen gradients? This will refine the mesh and your results should become more accurate.

Thanks Tang, I adapted the grid a lot, (many times, incrementally again to ensure no divergence) which helped.

I have ditched the Prepdf approach as it just wont work with my situation (no pressure increase as previously mentioned).

I am now using the h2/air mixture template and I have everything fine in non reacting conditions.

Now, I apply a patch to a register that I have set and it wont work again. The temperature increases (indicating combustion) but then after 5000 or so iterations, the chamber is cold again (no combustion).

Its getting really annoying now and it seems there is no such information on this forum ( I spent about 12 hours looking).

Thanks Jouch