Suppressing Restricted Shock Separation in Thrust-Optimized Rocket Nozzles Using Contour Geometry

Abstract

Restricted shock separation (RSS) is an undesirable flow phenomenon that occurs in thrust-optimized nozzles during the start-up and shut down of the engine. To determine if the nozzle geometry can be used to suppress RSS in rocket nozzles, a set of five equivalent thrust-optimized nozzle contours were generated using an arc-based design method. Variation between contours was achieved by manipulating the nozzle inflection and exit angle, and further explored through the use of dual arc segments in the expansion or turning curve in two equivalent contours. All nozzle variants were evaluated numerically using the predicted thrust coefficient, contours of Mach number, and static wall pressure distributions across start-up, initial, ideal and vacuum operating conditions. The RSS flow condition was prevented in three of the equivalent contours, where two of these configurations also predicted an increase in thrust at all operating conditions. The prevention of RSS in an additional nozzle contour was achieved through manipulation of the expansion curve at the expense of thrust. Comparatively, manipulation of the turning curve resulted in a relative thrust increase and favorable pressure distribution. The result indicates that the prevention of RSS independent of thrust may be achieved in an arc-based equivalent nozzle contour.