oxygen lance simualtion in vacuum

rensb

hi,friends

i am simulation the oxygen lance using in the steel ladle,the lance is laval nozzle and the operation condition is vacuum about 100torr, with the lower of the vacuum ,the velocity of nozzle exit will be large,but ,during my simualtion ,the difference of velocity maginitude of under difference vacuum is very small ,almost lower than 10m/s,however ,the data will be 100m/s in real situlation, what the matter with my simualtion?

thank your advice.

rensb