I am working on a project which involves air nozzles. I am interested in estimating the time it takes for air particles after they leave the nozzle to reach a particular distance away. I have the following information--- a converging nozzle, the speed with which it is coming out of the nozzle(I know when the air is choked it comes out at Mach number). I also believe that if the nozzle was blowing in vacuum, the air would continue travelling at Mach number. How would blowing out in "normal atmosphere" affect it? I just want a rough idea/guideline. Any help will be appreciated.