一种小长高比组合发动机喷管气动设计及性能分析

在强几何约束条件下，对一种Ma=0~6.0的小长高比组合发动机喷管气动设计开展了初步研究。采用特征线法设计程序开展了喷管型线设计，并对设计点马赫数选取、三维侧向膨胀角、喷管双通道相对位置对喷管气动性能的影响开展了研究，给出了兼顾空间有效利用与喷管气动性能的喷管气动设计方案。数值模拟结果显示:降低设计点马赫数可以改善组合发动机喷管在低马赫数飞行时的性能，避免喷管出现严重过膨胀；喷管保持出口高度不变时，随着侧向膨胀角的増大，其高马赫数气动性能较优，而低马赫数气动性能下降严重。涡轮/冲压发动机喷管出口相对位置对并联布局组合发动机喷管转级点气动性能影响较大，且存在一个最佳位置布局，使得转级点达到最优的推力性能。获得的组合发动机喷管在设计马赫数下的推力系数约为0.920，模态转换过程流场平稳过渡，推力系数不低于0.918。

Aerodynamic design and numerical simulation of combined cycle nozzle with small length to height ratio

A preliminary study on the aerodynamic design of the combined cycle nozzle working in the range Ma=0~6.0 with small length to height ratio was carried out under strong geometric restricts. The line of the nozzle was designed by the method of characteristic. The effects of the design Mach number, the three-dimensional lateral expansion angle and the relative position of the two nozzles on the aerodynamic performance were studied. A nozzle aerodynamic design scheme considering both the effective utilization of space and the aerodynamic performance was presented. The numerical simulation results show that reducing the Mach number at the design points can improve the performance of the combined cycle nozzles during the subsonic flight and avoid serious overexpansion of the nozzles. With the increase of the lateral expansion angle, the aerodynamic performance of the nozzle that keeps the exit height unchanged at high Mach number is superior, while the aerodynamic performance of the nozzle at low Mach number decreases seriously. The relative position of the turbine engine and the ramjet nozzle outlet has a great influence on the aerodynamic performance of the transition point, and there is an optimal position layout, which achieves the optimal thrust performance. The thrust coefficient of the combined cycle nozzle is about 0.920 at the designed Mach number. The flow field is smooth transition during the transition mode, when the thrust coefficient is not less than 0.918.