旋转爆震发动机喷管非定常流动特性的数值模拟研究

Numerical Investigation on Unsteady Flow of Nozzle in Rotating Detonation Engine

为分析旋转爆震喷管内非定常流动特性,基于特征线方法和旋转爆震燃烧室出口时均参数设计了一种塞式喷管模型,通过改变塞锥式喷管的进出口压比π(π=15,30,45),分析了喷管内非定常流场结构与喷管工作性能之间的相互关系,并探究了喷管进出口压比变化对喷管工作性能的影响。研究结果表明:旋转爆震燃烧室下游斜激波进入喷管后,在喷管内形成一道绕喷管壁面螺旋分布的激波,激波结构主要由波前气流角和激波前气流速度决定;爆震喷管局部工作状态依据相对螺旋激波位置分别存在自由膨胀状态、欠膨胀状态、欠膨胀与过膨胀过渡状态以及过膨胀状态四种情况,并随着激波的传播不断增强,在第四种工作状态达到最大(喷管处于过膨胀状态),且喷管在第二到第四种工作状态内工作性能变差;在低压比(π=15)工作条件下喷管性能优于高压比(π=30)工作条件下喷管性能,其最佳推力和燃料比冲分别为992.05N和1769.52s,因而旋转爆震喷管设计应选择较高的进出口压比作为设计点,使旋转爆震喷管更多的工作在低压比工作状态,以提高旋转爆震喷管工作效率。

To analyse the unsteady flow characteristics in the rotating detonation nozzle,a plug nozzle model is designed based on the characteristics method and time-average parameters of the rotating detonation combustor outlet. By changing the inlet/outlet pressure ratio of the plug nozzle(pressure ratios of 15,30 and 45 respectively),the relationship between the unsteady nozzle flow field and the performance of the nozzle is analyzed,and the effects of pressure ratio variation on the nozzle performance are investigated. The results show that after the oblique shock wave from the downstream of the rotating detonation combustor enters the nozzle,a spiral shock wave is spirally distributed around the plug nozzle wall,and the shock wave structure is mainly determined by the airflow angle and airflow velocity of shock wave front. According to the distribution of the spiral shock wave along with the plug nozzle,the working state of the detonation nozzle can be divided into four phases,such as free expansion phase,under-expansion phase,under-expansion to over-expansion transition phase,and over-expansion phase. The shock wave appears in the nozzle during the second stage(under-expansion),and the strength increases with the propagation of the shock wave,reaching the maximum at the fourth stage(the nozzle is at the over-expanded state). The nozzle performance is deteriorates during the second to fourth stages. The nozzle performance at a lower pressure ratio of 15 is higher than that at the high-pressure ratio of 30 and its peak thrust and fuel specific impulse are 992.05 N and 1769.52 s,respectively. Therefore,a higher inlet/outlet pressure ratio should be selected as a design point for the rotating detonation nozzle,consequently,the nozzle could work under a low-pressure ratio at more time to improve the efficiency of the nozzle.