Physical insight into scramjet inlet behavior via multi-objective design optimization

Scramjet propulsion is a promising technology for reliable and economical access to space and high-speed atmospheric transport. The inlet plays a key role in determining the performance of scramjets, in particular for the axisymmetric class of scramjet engines that are currently explored due to their advantages in numerous aspects. In the present study, a multi-objective design optimization based on evolutionary algorithms has been conducted with respect to four major inlet design criteria, that is, compression efficiency, drag, adverse pressure gradient, and exit temperature, where the former three criteria are used as the objective functions and the last one is the constraint function. The flowfields have been examined for representative geometries, and sensitivity analysis has been performed with the aid of surrogate modeling, revealing the major impact of the inlet exit radius, advantages of Busemann-type geometries in various aspects, and direct correlation of the inlet drag, exit temperature, and surfaceheat transfer. The insight gained here can be usefully applied to the design of high-performance scramjet inlets.