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李帅, 张阿漫, 韩蕊. 水中高压脉动气泡水射流形成机理及载荷特性研究[J]. 力学学报, 2019, 51(6): 1666-1681. DOI: 10.6052/0459-1879-19-219
引用本文: 李帅, 张阿漫, 韩蕊. 水中高压脉动气泡水射流形成机理及载荷特性研究[J]. 力学学报, 2019, 51(6): 1666-1681. DOI: 10.6052/0459-1879-19-219
Li Shuai, Zhang Aman, Han Rui. THE MECHANISM OF JETTING BEHAVIORS OF AN OSCILLATING BUBBLE[J]. Chinese Journal of Theoretical and Applied Mechanics, 2019, 51(6): 1666-1681. DOI: 10.6052/0459-1879-19-219
Citation: Li Shuai, Zhang Aman, Han Rui. THE MECHANISM OF JETTING BEHAVIORS OF AN OSCILLATING BUBBLE[J]. Chinese Journal of Theoretical and Applied Mechanics, 2019, 51(6): 1666-1681. DOI: 10.6052/0459-1879-19-219

水中高压脉动气泡水射流形成机理及载荷特性研究

THE MECHANISM OF JETTING BEHAVIORS OF AN OSCILLATING BUBBLE

  • 摘要: 具有脉动特性的气泡(如水下爆炸气泡、螺旋桨空泡和气枪气泡)动力学行为很大程度上取决于其边界条件. 实验已证实,近自由液面气泡在坍塌过程中常常产生背离自由液面的水射流现象,而近刚性边界气泡在坍塌阶段产生朝向壁面的高速水射流,严重威胁水中结构的局部强度. 前人基于 Rayleigh-Plesset 气泡理论和 “Bjerknes” 力来预测气泡射流方向,然而理论方法难以透彻的揭示气泡射流的初生、发展和砰击过程中丰富的力学机理. 本文首先采用水下高压放电技术产生气泡,并通过高速摄影对不同边界条件下气泡的运动特性进行实验研究. 然后,采用边界积分法模拟气泡非球状坍塌过程. 研究表明,边界条件改变了气泡周围的流场压力梯度方向,进而影响气泡射流初生位置;射流在发展阶段,气泡附近流场的局部高压区和射流之间存在“正反馈效应”,从而揭示了气泡射流速度在短时间内即可增加到百米每秒的力学机理. 射流砰击会在流场中造成局部高压区,随着气泡回弹,射流速度和砰击压力逐渐减小. 本文还探讨了无量纲距离参数对气泡运动及射流砰击载荷的影响,旨为近场水下爆炸等相关领域提供参考.

     

    Abstract: The dynamic behaviors of an oscillating bubble (e.g., underwater explosion bubble, cavitation bubble and air-gun bubble) are well known to be strongly dependent on the nature of boundary conditions. Many experiments demonstrated that a high-speed liquid jet is formed away from a free surface or towards a nearby rigid wall. The violent jet impact is believed to be one of the most important mechanisms of cavitation erosion and damages by an underwater explosion. In the previously published literature, the Kelvin impulse based on spherical bubble theory is adopted to determine the gross migration and jet direction of bubbles. However, the underlying mechanisms of jet inception and development are not fully understood and the characteristics of the jet impact still lack exploration. In the present work, both experimental and numerical methods are adopted to do some fundamental studies on bubble dynamics beneath a free surface and near a rigid wall. The electric discharge method is used to generate a bubble and the bubble motion is captured by a high-speed camera. Meanwhile, the boundary integral method is adopted to conduct numerical simulation. The presence of a nearby boundary alters the pressure gradient surrounding the bubble, which has a significant influence on the jet inception. Additionally, a local high-pressure region is generated near the bubble bottom, and it results in a positive feedback mechanism that further accelerates the jet. This mechanism reveals the fact that the jet can speed up to a hundred meters per second within a relatively short time. A localized high-pressure region is caused by the jet impact around the jet tip and the maximum pressure decreases gradually as the rebound of the toroidal bubble. At last, the effect of the dimensionless standoff parameter (defined as \gamma = d / R_m, where d is the distance between the initial bubble center and the rigid wall and R_m is the maximum bubble radius) on the jet impact pressure is discussed.

     

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