Numerical investigation of upstream fuel injection through porous media for scramjet engines via surrogate-assisted evolutionary algorithms

A multi-objective design optimization study has been conducted for upstream fuel injection through porous media applied to the first ramp of a two-dimensional scramjet intake. The optimization has been performed by coupling evolutionary algorithms assisted by surrogate modeling and computational fluid dynamics with respect to three design criteria, that is, the maximization of the mixing efficiency, total pressure saving, and fuel penetration. A distinct Pareto optimal front has been obtained, highlighting the counteracting behavior of the total pressure against fuel penetration, while the mixing performance crucially depends on the fuel/air equivalence ratio, as suggested by an additional optimization using the absolute mixing quantity. The Darcian and Forchheimer coefficients in the porous flow direction have been identified as the key design parameters in conjunction with the geometric parameters as a result of a sensitivity analysis. Flowfield visualization has revealed the presence of local hot pockets with intensely high pressure and temperature offered by a long injector positioned upstream due to augmented shock interactions.