水中冲击波作用下气泡溃灭的界面不稳定演化规律研究

It is a fundamental problem to investigate the bubble motion induced by an underwater shock wave for understanding the collapse mechanism of cavitation cloud. The motion of a bubble is mainly presented by the volume oscillation and interface instability. The former is that the bubble contract and generate rebound shock wave just after expanding from its minimum size resulted from the pressure of the shock wave. On the other hand, interface instability is caused with the generation of vorticity and bubble centroid displacement due to baroclinic effects. Furthermore, a high-speed jet can be formed in this process, impact, and penetrate the bubble wall so that the phenomena of water hammer and bubble fragmentation are caused. .As mentioned above, the interaction of bubble with underwater shock wave is relative to some sophisticated problems, such as numerous effecting factors, various motion types, complicated allocation laws for energy. The present project aims to clarify the interface instability problem of the bubble interface and mechanical mechanism of the jet generation, by an underwater shock wave interacting with a bubble in various types. In the study, we will carry out highly accurate measurements of velocity and pressure field, and an optical visualization to bubble behaviors. With combination of a theoretical and numerical method, the characteristics of the key physical processes will be analyzed, containing bubble centroid displacement, volume oscillation, rebound shock wave generation, jet formation, jet-induced water hammer, and bubble fragmentation. In the meantime, the distribution of vorticity will be also investigated around the bubble. As a result, effecting mechanism of main parameters will be obtained for allocation laws of energy. Finally, we will summarize the motion types of the bubbles and corresponding criterion for determining bubble behaviors. The relative laws of cognition provide theoretical value for modeling the collapse of the bubble.

冲击波作用下气泡响应作为研究空泡群溃灭机制的核心基础问题。气泡响应主要体现为体积变化和界面不稳定两种类型，前者指气泡体积收缩、膨胀运动，并在反弹瞬间生成溃灭冲击波；后者指界面在斜压等因素下发生不稳定，伴随涡环生成、气泡形心迁移，并可能产生射流。射流撞击、穿透气泡壁会造成水锤冲击现象和气泡分裂。.本项目针对该问题影响因素众多、响应类型和能量分配规律复杂的特点，以冲击波加载不同类型的气泡为研究对象，开展气泡界面不稳定性和射流生成内在力学机理研究。通过实验方法，包括高频响速度场与压强测量、高精度界面观察手段，结合理论与数值模拟方法，获得气泡迁移运动、体积振荡、溃灭冲击波生成、射流生成与发展等关键过程特征，分析冲击波与界面作用下涡量的生成条件和分布规律，揭示主控参数对气泡运动中能量分配的影响机制，总结归纳气泡响应不同类型和发生条件判据，相关规律性认识可为空泡群溃灭过程建模和计算提供理论重要参考。

空化是水动力学中重要现象，相变生成大量气泡，构成空泡群。空泡群溃灭不仅严重影响航行体水动力性能、产生噪音与振动，甚至能够剥蚀结构表面导致破坏。冲击波-气泡相互作用现象是空泡群溃灭的基本形式，因此，冲击波作用下空泡溃灭机制和溃灭作用下多界面耦合是解决问题的核心基础。.本项目通过实验验证、数值模拟和理论建模相结合的方式，开展了冲击波作用下空泡溃灭机制和气液界面稳定性研究。（1）以水中冲击波加载气泡为研究对象，关注气泡体积振荡、溃灭冲击波生成、射流生成、水锤效应等关键过程，通过定义泡内边界层厚度，引入泡内分子的热分解反应，分析了通过气泡壁面的热传导效应和质量传输，解释了泡内分子微观运动规律，建立了反映力/热/质量输运/化学反应的空泡溃灭理论模型。在均相混合物模型的基础上，引入气泡数密度表征空化区内部结构并气泡分裂因素，建立了反映微观空泡群动力学特性的宏观空化相变模型。将模型理论解作为神经网络的输入条件，结合型号部分的缩比实验数据，建立了融合物理信息的载荷预测智能模型，能够快速计算航行体受力与发射轨迹，有效体能型号设计能力。（2）针对航行器高速跨介质过程，建立了空泡振荡诱导自由面大变形的物理模型，发展了二维柱状液滴内激光空泡实验与数值方法，建立了有限空间空泡动力学方程与自由面扰动演化方程，揭示了Rayleigh-Taylor失稳导致的振荡、通气和破碎机制，获得了不同控制参数下空泡诱导自由面变形的流态相图。相关结论揭示了自由面与非稳态空泡的耦合影响机制，为跨介质航行体溃灭载荷机理分析及界面演化流态预测提供了重要支撑，寻找到的稳定减阻流态已应用于新概念水面超高速航行器研制，遴选为2021年某gf领域重大进展。相关工作发表在J. Fluid Mech.、 Ultrason. Sonochem.、 J. Appl. Phys.等相关领域重要期刊。2019年，获得美国机械工程师协会（ASME）CFD 领域年度最佳论文奖。2020年入选中国科协青年人才托举工程项目，2021年，入选力学所“优培计划”B类和中国科学院青年创新促进会。