Numerical Investigation of Supersonic Exhaust Diffuser

High expansion rocket engines which are designed to operate at high altitudes need to be tested at ground level. The upper stages of multistage space vehicles require rocket engines with large area-ratio exhaust nozzles to take advantage of the high specific impulse potential. When these engines are tested at sea level conditions, the flow separates in the divergent part of the nozzle due to lack of low pressure environment outside the nozzle. In the development process, such rocket engines must be operated under conditions that permit full expansion of the flow in the engine nozzle. To accomplish such operation at sea level, it is necessary to provide some means of reducing the ambient pressure so that the gases from the exhaust nozzle expand fully. Supersonic exhaust diffusers are the only means of providing altitude simulation for rocket engine performance evaluations in a High Altitude Test facility. These facilities utilize Supersonic Exhaust Diffusers of constant area type or varying area type Second Throat Exhaust Diffuser, which are simple and inexpensive devices for evaluation of steady state performance of the rocket nozzles.