Effects of secondary injection on the performance of over-expanded single expansion ramp nozzle

Abstract

Scramjets with Single expansion ramp nozzle (SERN) is one of the most promising candidates for an airframe integrated hypersonic vehicle propulsion system. So, studying the performance of the SERN at various flight conditions is very important to improve the overall performance of the propulsion system. The main problem with a SERN is, it tends to exhibit poor performance characteristics at the over-expanded or off-design operating conditions. So, to improve the performance of the SERN at off-design conditions, the present numerical study focuses on using various secondary injection techniques on the cowl and ramp surfaces. The freestream Mach number considered for the current study is 3, and the corresponding nozzle pressure ratio (NPR) for the SERN is 20. The effects of injection pressure, location, and angle on the axial thrust force and normal force are parametrically studied. It is found that the introduction of secondary injection significantly affects the pressure distribution over the cowl and ramp surface. This change in pressure distribution directly reflects on the magnitude of the normal force and axial thrust force generated by the SERN. The secondary injection also influences the shock pattern of the main nozzle flow.