Aerodynamic design optimization of the hypersonic inward turning inlet in wide-speed range

A multipoint optimization based on the discrete adjoint optimization method in a wide-speed range is carried out to improve the performance of the hypersonic inlet with a rectangular to elliptical shape transition. The optimization framework is established based on the discrete adjoint method and combined with the free form deformation method, the mesh deformation method, and the high-accuracy Reynolds averaged Navier-Stokes solver. A total of 3180 design variables are employed during the optimization, and the optimum result is obtained after 67 iterations of adjoint optimization. The results indicate that the performance of the optimized inlet is significantly improved under both design and off-design conditions, while better improvements are obtained under off-design conditions. Thereafter, the mechanism of the performance enhancement is investigated by comparing the flow patterns of the original inlet with the optimized inlet under different operating conditions. Furthermore, the optimization results demonstrate that requirements for the localized deformation to enhance the inlet performance at each Mach number may be contradictory because of the different flow patterns under various operating conditions. As a result, the optimized result can be only a tradeoff between the constraints in wide-speed ranges.