Effects of Limitation of Nozzle Flow Separation on Launcher Performance

Abstract

Limitations induced by flow separation at liftoff of launcher core engines can be overcome with the use of a new nozzle concept recently proposed. This device is able to prevent separation in an overexpanded nozzle. Consequently, a lower nozzle-exit pressure is possible at sea level and low altitudes, allowing for engine throttling or for the use of a nozzle with larger nozzle expansion-area ratios. To assess the actual potential of payload growth given by the application of such a device, the ascent trajectory must be evaluated and possibly optimized. A fast and reliable in-house code, based on the optimal-control theory, is used to optimize the ascent trajectory. Results show that the ideal velocity gain can be increased with throttling. However, ascent losses offset this benefit and reduce the actual payload; in any case, the launcher experiences lower dynamical loads and gains flexibility. On the other hand, payload improvements from the increase in the nozzle expansion-area ratio of the core engine may be obtained, depending on how large the penalty of the increased nozzle weight is.