Hello, this is my first post. I have been using FLUENT for a while and have this problem that has been troubling me quite a bit lately. I am using FLUENT 5.5 and am running a 2-D unsteady transonic/supersonic combustion case. The fuel is simpley H2 and the inlet is from a profile at Mach around 2.5 if that matters any. My problem is that as the time steps increase (the problem even occurs with steasy flow) I have a zone right downstream of the fuel inlets (one top and bottom) which inject at M=1 where the temperature tries to drop to zero, thus resulting in a divergance. The fuel is at 233 K static temp. so I limited the minimum temperature to 100 K and played around with the positivity limit. CFL is 1.0, changing that appears to have no affect. the number of cells with this problem vary from 100 to 3000. I am using implicit method and try time steps from 1e-6 to 1e-5, nothing is working. explicit does not allow the residuals to drop below 1e-1 so I know that does not work. Would multi-grid affect anything? (I am not too familiar with that but if anyone knows if it might work, I will mess around with it.) The grid apears to be fine, no major jumps etc. so I doubt that is the problem. PLEASE!!, If anyone can help or has any input please let me know. Thankyou in advance for any help you all can offer. -Nathan L.

This is a continuation of my message, I am using 2nd order explicit, not implict, that does not do anything but diverge. Thanks again for any help that can be offered