Variable area ejectors for increasing the compression factor of an RBCC Engine

The present paper details the effects of using exit area constriction on the compression ratio achieved of an axisymmetric ejector incorporating both a central and annular rocket exhaust configuration for use in a Rocket Based Combined Cycle engine. Steady state solutions of the axisymmetric Favre averaged Navier-Stokes equations closed by the Wilcox km turbulence model (including the Wilcox dilatational dissipation correction) are obtained using WARP, a finite difference flow solver using the Yee-Roe flux limiting scheme. It is shown that decreasing the exit area by 25% over the entire length of an ejector can produce an increase of 23% in the compression ratio compared to a constant area ejector under the same operating conditions. Further, it is shown that using a conical/cylindrical configuration can increase the compression ratio by a further 5-7% over the conically constricting configuration resulting in an overall increase of approximately 30 % (for a ratio of air to rocket exhaust massflows of approximately 0.75).