Supersonic mixing in airbreathing propulsion systems for hypersonic flights

Achieving efficient fuel-air mixing is a crucial problem for the design of scramjet engines. Due to the very short residence time of the fuel within the scramjet combustor for typical flight conditions, an efficient injection strategy with high penetration depth and rapid mixing is required. For this reason, many mixing augmentation devices have been proposed and investigated, namely wall injection, struts, ramps, cavities, vortex generators and new configurations developed in China. In this survey, their mixing augmentation mechanisms are analyzed and the numerical and experimental studies are described which have been performed for the assessment of their mixing effectiveness. Some novel insights are provided to further the development of large-scale scramjet engines at increased flight Mach number. The need for additional research based on improved numerical approaches and experimental facilities is stressed.