【作者】 吉晨；

【导师】 邹俊； 傅新；

【作者基本信息】 浙江大学 ， 机械电子工程， 2013， 博士

【摘要】 气泡广泛存在于自然界的液体之中,从多方面影响着我们的生活。局部压力的降低会使液体发生空化而产生蒸气泡(又称空泡),并经历发展、溃灭和回弹等一系列动力学过程。外界气体也可通过多种方式进入液体之中形成气泡,同时液体中存在的微量气体作为“气核”对空化的发生有重要的促进作用。气泡的行为对自然界中的许多现象具有重要的意义,在流体机械、液压系统、水工结构中造成振动、噪声、空蚀等多种危害,在生物医学、MEMS和工程领域则有广泛的应用前景。长期以来,气泡行为的研究是流体动力学研究中的热点领域。但是,现有关于在受限制空间中气泡行为的研究较少,而这一问题对于气泡的科学认识和应用都有重要的基础性意义。本文结合理论分析、数值模拟和高速摄像观测等手段,对受限制空间中的气泡行为开展了较为系统和深入的研究。总结了约束液面形成冲击气泡的各种现象,得到了液滴冲击约束液面现象的无量纲参数域,分析了壁面约束和液滴振荡对冲击气泡形成过程的影响机理。定量分析了反气泡的溃灭过程,建立了溃灭速度模型。观察了管道内空泡的动力学行为和双空泡干涉现象,建立了管道内空泡动力学行为的BEM数值模型,分析了管道约束对空泡行为的影响规律,揭示了管道内单空泡／双空泡动力学行为的机理。论文的主要内容如下：第一章,绪论。阐述了本课题研究的背景与意义；综述了冲击气泡形成过程和空泡动力学行为的研究历史与现状；概括了本文的主要内容。第二章,空泡动力学数值模型研究。采用BEM方法建立了空泡动力学数值计算模型,阐述了其控制方程、边界积分方程、离散化方法、算法设置和计算流程,针对空泡发展过程中拓扑形状的变化给出了相应的数值处理算法。第三章,约束液面冲击气泡形成研究。总结了受约束液面形成冲击气泡的四种类型,给出了冲击现象的参数平面分布图；分析了壁面约束对延时气泡、大气泡和穹顶气泡等现象的影响,提出液滴形状振荡是大气泡形成区域间断分布现象的原因；发现反气泡开始溃灭后极短时间内可达到稳定的溃灭速度,建立反气泡溃灭速度的计算模型,发现溃灭速度与(б/pe)1/2成正比。第四章,管道内空泡动力学行为及双空泡干涉的研究。通过高速摄像观察了管道内单空泡的形态演化,采用数值模拟研究了特征参数对空泡体积和周期的影响；观察了管道内的双空泡干涉现象,得到了干涉现象的参数区域分布图,通过数值模拟分析了管道内双空泡干涉的机理。第五章,总结与展望。对论文研究工作和创新点进行了总结,对后续的研究工作进行了展望。更多还原

【Abstract】 Bubble is a common phenomenon in liquid. Vapor bubbles are formed by cavitation due to the decrease of local pressure, which will develop, collapse and rebound in the liquid. Other bubbles consist of external gas entrapped in the liquid, which play an inportant role in cavitation process as cavitation nuclei. Bubble causes several serious problems in fluid systems, such as vibration, noise and cavitation erosion. On the other hand, bubble can be widely applied in the areas of medical treatment. MEMS and engineering, while it is also a pivotal element in many natural processes. Although bubbles have attracted attention of many reaseachers. investigation on the behavior of bubbles in restricted space is uncommon in literature.In this thesis, the behavior of bubbles in restricted space is studied systematically and comprehensively, by means of theoretical analysis, numerical simulation and high-speed camera observation. The phenomena of bubble entrainment during drop impacting on restricted liquid surface are summarized. The effects of the restircting wall and the vibration of drop are analysised. The regimes of various outcomes of drop impact are given on non-dimentional parameter plane. The collapse of antibubble is studied quantitatively, to derive a model of the collapse velocity. The dynamic behavior of single/double spark-induced bubble in tube is observed by high-speed camera. BEM numerical model for the bubbles in tube is presented, with which the effect of tube wall on the behavior of the bubble is presented, and mechanism of single/double spark-induced bubble in tube is analysised.The outline of this thesis is as follows,In chapter1, the background and significance of the thesis are proposed. Literature on the bubble formation during impacting process and the dynamics of cavitation bubble are reviewed. The main content of the thesis is summarized.In chapter2, BEM numerical model for the dynamic behavior of bubbles is presented, which is able to deal with bubble coalescence and ring bubble. The governing equations, boundary integral equations, descretization. calculation programme and other algorithms are introduced.In chapter3, the phenomena of bubble entrainment during drop impacting on restricted liquid surface are summarized into four types. The regimes of various outcomes of drop impact are given on parameter plane. The effects of restricting wall on delayed bubble, large bubble and canopy bubble are analysised. The discrete Weber number regime of large bubbles is reported, which is caused by the shape oscillation of the drop. A model of the collapse velocity of antibubbles is derived, which shows that the collapse velocity is proportionate to (σ/pe)1/2.In chapter4, the development and collapse of single spark-induced bubble in tube is studied, whose volume and vibration period are analysised by numerical simulation. The interaction of two spark-induced bubbles is observed by high-speed camera. The mechanism of two bubble interaction is analysised, and the regimes of various phenomena are presented on parameter plane.In chapter5, the research work of the thesis is summarized with further prospect.更多还原