05-04-2017, 02:56 PM
In a bell nozzle the combustion gases flow through a constriction (throat) and then the expansion away from the center line is contained by the divergent walls of the nozzle to the outlet plane. Nozzles are a punctual design with optimum performance at a specific ambient pressure (ie, altitude). Careful design is required to achieve the desired altitude performance, avoiding the separation of flow in the nozzle walls near the outlet when operating at low altitudes (launch), which can lead to loss of performance and possible structural failure Of nozzle due to dynamic loads [Flow separation is responsible for movement of large nozzle in SSME during transient start - close-up monitoring during next launch]. Therefore, a compromise altitude should be used for the design point of a bell nozzle. The aerospike engine is so named because the nozzle resembles a peak. A stopper nozzle is a truncated aerospike nozzle.