COMPUTATIONAL FLOW SIMULATIONS OF OVEREXPANDED ROCKET NOZZLE FLOWFIELDS INCLUDING UNSTEADY EFFECTS

摘要

The operation of rocket nozzles remains a very critical issue for reliability and performance of space launchers. The major difficulty in the design of a sea-level operating nozzle is that the optimization requires a compromise between sea level conditions and vacuum conditions. This is the case for first or second stage booster engines as well as for single-stage-to-orbit engine. For such rocket engines, the vacuum conditions will be reached during most of the duration of the flight, so that the engine performance in vacuum will be the main factor in the flight performance. However, the optimization of the design can not be based only on these particular conditions, as it is for upper-stage nozzles. Two specific constraints due to the operation at sea level during the early time of flight must be taken account: Flow separation in the nozzle due to non-zero external pressure, and side loads during start-up due to non axi-symmetric flow separation. Different actions have been initiated in Europe to to deal with these different complex issues. The present paper will report about the modelling effort carried out in this general frame to progress forward in the field of numerical simulation and modelling capabilities.