Design Method for Scramjet Nozzles Under Geometric Constraints

This paper presents a novel design method for scramjet nozzles under geometric constraints. Performance optimization theory is incorporated in both the expansion flows along the ramp and the cowl. Method of characteristics is implemented to determine the nozzle configuration, and numerical methods are adopted to obtain the performance parameters and flowfield of the designed nozzle. The results denote that both the initial expansion angles of the ramp and the cowl have significant influence on nozzle performance, and there is an optimal value in the initial expansion angle of the cowl for maximum thrust. The changing tendency of axial thrust coefficient is opposite to that of lift and pitching moment, as the initial expansion angle of the ramp increases. The designed nozzle obtains significant increases of 11.14 and 917.20% in axial thrust coefficient and lift, respectively, as compared with the common nozzle designed by the truncation method. It also enhances the pitching moment by 3.90% for the trimming of the vehicle. Compared with the previous method, the scramjet nozzle obtained by the present design method can realize higher efficiencies for scramjets under geometric constraints.