COMSOL gas jet

jm

Hello,

I'm using COMSOL MP v3.3 to model the flow of a cylindrical gas jet out of a nozzle (diameter 4mm) into a volume at atmospheric pressure and room temperature. The inlet velocity is 100m/s and the temperature at the nozzle is 1400K. I'm using the Fluid-Thermal-Interaction-Application-Mode, which basically couples the Non-Isothermal-Flow-Mode with the General-Heat-Transfer-Mode.

As some back-of-the-envelope-calculations showed the loss-processes conduction and radiation don't seem to balance the heat-transport into the volume through convection. I haven't figured out how to get the radiation losses into COMSOL and up to now I couldn't find more loss-processes, but I'm working on this.

I managed to solve the stationary problem, when only considering conduction and convection. In this solution the pressure equals atmospheric pressure almost every where. Only right in front of the nozzle there seem to be some fluctuations: +5Pa in the middle and -1Pa at the edge of the nozzle. I can't imagine that there's only such a small variation in pressure, when the velocity is quite high. Has anyone experience with this?

Furthermore the jet remains very focussed and caused by variations in density due to the high temperatures the velocity-field outside the jet points in the direction of the center, but these velocities are really small, and there's no cooling effect.

I used a linear velocity-distribution over the nozzle: (1-s)*100m/s. I'm not sure if the velocity at the edge of the nozzle really equals zero and there seem to be no vortices or eddies near it when using some finite velocity at the nozzle's edge.

The only eperimental results I can rely on at moment is some temperature-measurement. I would be really glad if someone who has some experience could give me some advice.

thx