固体火箭发动机水下超音速射流数值研究

固体火箭发动机水下点火射流是高温高压条件下复杂的多相流过程，为研究其流场特性与推力特性，选取扩张比分别为3.4和14.0的拉瓦尔喷管模型进行数值模拟。采用计算流体力学方法分析高速燃气超音速射流过程的流场与推力演化过程，揭示高温高压气体与水环境之间的相互作用规律。结果表明：固体火箭发动机水下射流流场结构与推力特性呈周期性变化，根据流场特征可分为颈缩、胀鼓、回击3个阶段；水环境与射流气体之间的相互作用是导致背压振荡的直接原因，同时导致激波运动、动量推力与压差推力的振荡。对比两种扩张比喷管的射流可知，扩张比为14.0的喷管射流形貌与流场结构的周期性变化更明显，扩张比为3.4的喷管背压振荡频率高、周期性特征弱、推力更稳定。

Numerical Study of Underwater Supersonic Gas Jets for Solid Rocket Engine

The ignition process of gas jets under water is essentially complex, including multiphase flow and complicated flow structures. The Laval nozzle models with expansion ratios of 3.4 and 14.0 are numerically simulated. The CFD method is applied to study the flow structures and corresponding thrust characteristics of rocket engine and analyze the interaction between the high-speed gas jets and water environment. The results show that the flow structures and thrust characteristics of engine change periodically, and the process can be divided into three stages: necking, bulge and return stroke. The interaction between the water environment and the gas jet is the immediate cause leading to the back pressure oscillation, which also induces the fluctuation of shock waves, momentum thrust and pressure differential thrust. For the nozzles with different expansion ratios, the periodic variation of jets pattern and flow structures for the nozzle with expansion ratio of 14 can be more obviously observed, and the oscillation frequency of back pressure for the nozzle with expansion ratio of 3.4 is higher, accompanied with weak periodic characteristics and more stable thrust characteristics.