Design of an Asymmetric Scramjet Nozzle with Circular to Rectangular Shape Transition

Abstract

A novel method for optimizing the shape of a three-dimensional scramjet nozzle with circular to rectangular shape transition, which aims to improve airframe integration, is presented in this paper. To generate the shape of the nozzle, the streamline tracing technique is used based on an annular optimum thrust nozzle flowfield calculated using the method of characteristics. The research is conducted using both the computational fluid dynamics approach and wind-tunnel experiments. Viscous flowfields are computed under the design conditions using commercial software Fluent in order to access the aerodynamic performance of the nozzle. The obtained computational fluid dynamics results on flow static pressures on the upper and lower walls of the three-dimensional nozzle have been validated against the measurement data. Comparisons of the computational fluid dynamics and wind-tunnel experimental results have been conducted under two specific nozzle pressure ratios; that is, underexpansion condition with nozzle pressure ratios equal to 70, and overexpansion condition with nozzle pressure ratios equal to 10. It is confirmed that the proposed method is convenient and accurate for designing a three-dimensional circular to rectangular shape transition scramjet nozzle. In comparison with a conventional thrust optimized model, the proposed nozzle designed by streamline tracing technique obtains an increase of thrust by 1.0% and lift by 92.5% under the same conditions. Furthermore, the area ratio of the nozzle designed by this method is 4.2% smaller than that of a thrust optimized one.