喷管结构形式对两级PDE性能的影响分析

为了研究喷管结构形式对两级 PDE 性能的影响及作用规律，以氢气和空气混合物为例，采用 FLUENT 软件中的 k-ε湍流模型，使用非平衡壁面函数、PISO 算法及基于梯度的动态自适应网格加密方法，对收敛、扩张、收扩等不同喷管结构形式的凹面腔内环形向心射流聚心碰撞产生激波会聚起爆爆震波的过程进行了数值模拟，并对两级脉冲爆震发动机产生的推力和冲量进行了计算。通过对不同时间点凹面腔产生的推力和冲量、喷管产生的推力和冲量、两级 PDE 总的推力和冲量三者之间的对比和分析，发现凹面腔产生的推力和冲量是两级 PDE 总的推力和冲量的主要来源，不同喷管结构形式对两级 PDE 推力和冲量性能的影响有较大的差别。以冲量为例，收敛喷管可以提高凹面腔的冲量，但是由于自身同时产生过多负的喷管冲量，因而总冲量较小；扩张喷管虽然对凹面腔冲量的提高作用不大，但是由于其自身可以提供正的喷管冲量，所以总冲量较大；收扩喷管的收敛段也可以较小幅度的提高凹面腔冲量，但同时产生的负喷管冲量会和扩张段产生的正喷管冲量发生抵消，使总的喷管冲量比较低，发动机总冲量也较小。综合考虑各方面因素，扩张喷管性能最优。可见在两级 PDE 喷管结构形式的选择上，要同时考虑凹面腔冲量和喷管冲量，权衡两者，才能选择出合适的喷管。

Investigation on the influence of nozzle configuration on performance of a 2-stage PDE

In order to investigate the influence of nozzle configuration on detonation initiation in a two-stage pulse detonation engine,detonation initiation processes using hydrogen-air mixture were simulated with different structural forms of nozzle including converging nozzle,converging-diverging nozzle,and diverging nozzle.A finite volume method with unstructured meshes refined moving self-adaptation and realizable k-ε turbulence model in software FLUENT were employed in the simulation. The non-equilibrium wall functions were used near wall and the PISO algorithm was employed in the calculation.Then the thrust and impulse performance of the two-stage pulse detonation engine with different structural forms of nozzle were calculated.Through comparative analysis of the thrust and impulse performance among the reflector,the nozzle,and the 2-stage PDE at different points during the detonation procedure the simulation results indicate that the thrust and impulse produced by the reflector is the major source of the total thrust and impulse produced by the 2-stage PDE,and the three nozzles have different influence on the two-stage pulse detonation engine.Take example for impulse,the converging nozzle is conducive to increasing the impulse of the reflector,but there is bigger negative nozzle impulse produced by itself at the same time,so the total impulse produced by the 2-stage PDE is smaller.And the convergent section of the converging-diverging nozzle is also in favor of smaller increase in the impulse of the reflector,but the negative nozzle impulse produced by itself at the same time offsets the positive nozzle impulse produced by the divergent section of the converging-diverging nozzle,as a result,the total impulse produced by the converging-diverging nozzle and the 2-stage PDE are both smaller.While the diverging nozzle hardly helps the increase in the reflector impulse,there is bigger positive nozzle impulse produced by itself,so the total impulse produced by the 2-stage PDE is bigger.With comprehensive consideration of various factors,the 2-stage PDE with the diverging nozzle is the best one.Therefore,compromise between reflector impulse and nozzle impulse is needed to select an appropriate nozzle configuration for this 2-stage PDE.