very large temperature gradient at outlet
 

Hello Foamers,
i have got a very difficult problem to handle. i want to simulate a discharging process in a plasma torch . i have the following boundary conditions:
at gas inlet for pressure zerogradient, wavetransmissive for outlet. the other interfaces coupled with solid region i have zerogradient. interal field 1.01e5 pa.
at gas inlet for velocity i use flowRateInletVelocity which defines fixed volumetricFlowRate. At all the other boundaries i use zeroGradient.
for temperature i have the greatest problem. I defined a fixedValue at inlet of 500K, at interface with solids i use turbulentTemperatureCoupledBaffleMixed condition. At outlet i use inletOutlet for temperature.BUT! i had to define the internal field temperature to 5000K because without so high starting temperature the simulation can not simply continue.
so i will have very large gradient at outlets.(5000 to 500K), at the beginning of the simulation it was OK, but the temperature at outlet will drop down suddenly in the meantime and cause divergence.
any advice from you is welcome!