Abstract: The effects of the cowl lip angle on total pressure recovery, drag performance and starting ability of a two-dimensional axisymmetric hypersonic inlet are investigated and a cowl lip angle is designed. The configuration of the cowl is first parameterized by a 3rd B-spline, and various inlet configurations with different cowl lip angles are obtained. Numerical simulation is then conducted to investigate the effect of the cowl lip angle on inlet total pressure recovery performance, drag performance, as well as starting ability. Results show the existence of an optimal cowl lip angle for the inlet to achieve the best total pressure recovery performance. It is found that a strong cowl shock stands at the entrance of the inlet with a small cowl lip angle, a convergent shock stands in the internal contraction region of the inlet with a large cowl lip angle, and both will cause serious total pressure loss. In the study of drag performance, the drags of both the inside and outside cowls can be effectively reduced by decreasing the cowl lip angle, while the drag of the compression wall increases due to the shock/boundary layer interaction. Affected by the three factors, the total drag decreases initially and then increases with the rise of the cowl lip angle. An optimal cowl lip angle also exists to achieve the best starting performance for the inlet with the same internal contraction ratio. In addition, when the cowl lip angle is too small, the large scale separation bubble of the unstarted inlet is hard to be swallowed, while the separation bubble forms a stable residence in the internal contraction region when the cowl lip angle is too large. Finally, the effect of the cowl lip angle on aerodynamic performance of inlets with various internal contraction ratios is explored and the design of the optimal cowl lip angle is discussed. Results show that the cowl lip angles to achieve the best total pressure recovery, the minimum drag and the best starting ability, respectively, are not the same; however, generally speaking, the differences among them are insignificant. Therefore, the researched inlet can achieve good total pressure recovery performance, drag characteristic, and starting ability simultaneously with a reasonable cowl lip angle.

Key words: two-dimensional axisymmetric hypersonic inlet, cowl lip angle, total pressure recovery, cowl shock, drag characteristic, starting ability