Jet Flow
 

Hi,

I am doing a simulation of jet flow from a converging nozzle. One result that I am getting is that the centerline velocity of the jet increases for a couple of mm after exiting the nozzle as opposed to maintaining the exit velocity as I would have expected.

Would anyone be able to explain this?

Thanks

after exiting, the flow will expand. So it basically like a converging-diverging flow. if it is subsonic during converging and sonic at exit, then it will go supersonic after exiting. However, this can not last long. a normal (barrel) shock wave will form and the velocity drops. It is difficult to model shock wave. so simulation can only give you a rough picture.