Optimal Shape Design of Supersonic Bypass Inlet

A relaxed isentropic compression supersonic inlet is a new concept that produces smaller cowl drag than a conventional inlet, but incurs lower total pressure recovery and increased flow distortion in the (radially) outer flow path. A supersonic inlet comprising a bypass annulus to the relaxed isentropic compression inlet dumps out airflow of low quality through the bypass duct. Our previous work of flow analysis of the complex bypass configuration revealed that the blockage due to complex three-dimensional geometries in the bypass duct causes a significant degradation of inlet performance by pushing the terminal normal shock upstream. The flow blockage is caused by an abrupt change of curvature in the bypass flow passages; a careful tailoring of the strut shapes would allow much better inlet performances. Here we conduct optimal design of strut shapes in the bypass annulus to maximize inlet mass flow rate at engine fan face. The incomplete sensitivity is adopted for efficient sensitivity analysis. Through the optimal shape design of the bypass duct, the inlet performance is recovered very close to the initial design intent of the axisymmetric supersonic inlet. The reason of the discrepancy between axisymmetric and design configurations is also discussed.