Segment V11.3: Rocket Engine Start-Up

(Related to Textbook Section 11.4.2 - Converging-Diverging Duct Flow)

A converging-diverging nozzle is used to accelerate a gas to supersonic speeds. The nozzle exit pressure is determined by the stagnation pressure upstream of the nozzle and nozzle area ratio. Unlike subsonic flows, the exit pressure for supersonic flows need not be equal to the surrounding pressure.

At lift-off conditions, the nozzles of the Space Shuttle rocket engines are overexpanded. The nozzle exit pressure is less than the surrounding sea level atmospheric pressure. As shown in a computational fluid dynamics (CFD) simulation of the start-up of the Space Shuttle engines, this situation causes a complex multidimensional flow in the exhaust plume. (Video courtesy of NASA. CFD simulation created by Dr. Carey Cox; copyright Mississippi State University Engineering Research Center.)