水下爆轰燃气泡形态与激波传播过程研究*(爆震专刊)

针对脉冲爆轰发动机在水下工作过程中形成的燃气射流问题,搭建了水下爆轰燃气实验系统,研究了第一个爆轰循环在水下的燃气泡发展变化过程。建立了基于气液两相双流体模型的脉冲爆轰发动机水下喷射模型,采用时-空守恒元和求解元方法,模拟了爆轰波退化为激波在水中的传播及衰减过程。研究结果表明：燃气泡前期受外界水环境阻滞作用呈现“豌豆状”形态,充分发展阶段气液交界面逐渐失稳,在达到最大尺寸后开始收缩并在中心轴线位置出现凸出的射流；水下爆轰燃气射流发展过程中同时存在脱离燃气泡的水中前导激波和管口燃气泡内的高压区两部分,水中前导激波在传播过程中压力迅速衰减至常压量级,而管口燃气泡内则一直保持较高压力；中心轴线区域气液交界面处反射激波的回传使管口附近出现回击现象,并导致前导激波波阵面上压力峰值逐渐出现在30°方向上。

Study on the Bubble Shape and Shock Wave Propagation Process of Underwater Detonation

An underwater detonation gas experiment system was established to explore the problem of detonation gas jet formed in the underwater working process of Pulse Detonation Engine (PDE). The development and changing process of gas bubble in the first detonation cycle of PDE was experimentally investigated. An underwater jet model of PDE based on the two-fluid model was established and the space-time conservation element and solution element (CE/SE) method was employed to numerically simulate the propagation and attenuation process of shock wave degenerated from detonation wave launching into water. The results show that the gas bubble is in the shape of "pea" as it is blocked by the external water environment in the early stage. The gas-liquid interface gradually loses its stability and starts to shrink in the process of full development, then a jet appears on the central axis after the gas bubble reaching the maximum size. During the development of the underwater detonation gas jet, there exist two high pressure region simultaneously which are the leading shock wave separated from the bubble and the area in the gas bubble near the nozzle. Pressure of the leading shock wave decays rapidly to the level of ambient pressure in the propagation, while the pressure field in the gas bubble keeps high level. The return of the reflected shock wave from the gas-liquid interface near the central axis area results in the return stroke near the nozzle, which causes the maximum pressure on the leading shock wave front to appear in 30° direction.