Abstract: When a submarine launched missile is ejected from the launch tube with a gas-steam ejection system, the tail will be attched with gas bubble, the development state of the tail cavitation will affect the establishment of the underwater ignition gas jet flow field. In order to figure out the mechanism about the structure of underwater launching flow field in different working conditions, mixture model and dynamic mesh method are adopted to simulate the dynamic flow field of gas jet under the three wrapping states of the engine in the tail cavity, which included expansion stage, early contraction stage, complete closure, and the corresponding ignition positions are 2.2m, 4.3m, 6.5m, respectively. The simulated results show that the greater the degree of tail cavity shrinkage, the more complicated the flow field structure in the engine nozzle is, the expansion and necking of the tail cavity make the launching platform suffer greater pressure pulsation. When the tail cavity is not in the contraction stage and the engine is ignited at a certain safe distance (4.3m)，it is beneficial to the establishment of the gas jet flow field, and the pressure fluctuation on the launch platform is the smallest, thus it effectively improves the safety of underwater ignition and launching.

Key words: Tail cavity;Underwater ignition;Gas jet;Dynamic mesh;Launch platform

摘要： 潜射导弹蒸汽-燃气弹射出筒时，弹尾会附着燃气泡，该尾空泡的发展形态会对水下点火燃气射流流场的建立产生影响。为了研究水下发动机不同工作状态发射流场结构变化及原因，采用Mixture模型和动网格技术对发动机处于尾空泡的三种包覆状态：扩张初期、收缩初期、完全闭合状态（对应点火位置分别为2.2m，4.3m，6.5m）的燃气射流动态流场进行数值模拟。仿真结果表明，尾空泡收缩程度越大，发动机喷管流场结构越复杂，尾空泡不断地膨胀-颈缩，使得发射平台受到较大的压强脉动；当尾空泡未处于收缩状态阶段且发动机运动一定安全距离4.3m时点火，既有利于燃气射流流场的建立，同时发射筒及艇体受到的压力脉动最小，从而有效地提高了水下点火发射的安全性。

关键词: 尾空泡;水下点火;燃气射流;动网格;发射平台