【作者】 刘秀梅；

【导师】 陆建； 倪晓武；

【作者基本信息】 南京理工大学 ， 仪器科学与技术， 2009， 博士

【摘要】 本文从理论、数值模拟和实验方面研究了激光空泡膨胀和收缩全过程及空泡溃灭诱导的射流对靶材的损伤机制,系统讨论了液体粘性、表面张力、温度、含气量以及材料弹性模量变化对空泡膨胀、收缩及溃灭过程的影响。首先从空泡动力学基本理论出发,得到了空泡各特征参量之间的关系,进而对空泡动力学模型进行了修正;采用有限差分法数值模拟不同参量液体中空泡的脉动行为,研究了液体粘性、表面张力、温度、含气量以及可压缩性等参量变化对空泡泡半径、泡壁运动速度、加速度以及溃灭周期等特征参量的影响。数值计算结果表明液体参量是影响空泡脉动的重要因素,它们将对空泡膨胀和收缩过程产生显著的影响。其次,采用基于光纤耦合的光束偏转测试系统进行了实验研究,探测了高功率激光烧蚀水下靶材所产生的激光等离子体冲击波、空泡等物理现象及空泡溃灭后期产生的射流对固壁面的冲击作用。深入分析了液体粘度、表面张力、温度等参量与空泡泡半径、泡壁运动速度、溃灭周期和靶材所受射流冲击力之间的定量关系,并通过数值计算进行了验证,给出了相应的理论解释。此外,考虑到固壁面对空泡溃灭周期的延长作用,对Rayleigh公式进行了修正,并根据修正后的Rayleigh公式建立了液体参量与射流速度、射流冲击压强大小之间的定量关系。实验研究结果表明液体粘性将减缓空泡膨胀和收缩过程,减小靶材所受射流冲击力,因而对空化起抑制作用;而表面张力延缓空泡膨胀加速空泡溃灭,增大靶材所受射流冲击力,促进了空化的作用效果。此外,还研究了液体温度变化对空泡动力学行为的影响。通过针对不同弹性模量的固壁面附近空泡脉动过程的研究,得到了壁面弹性模量变化对空泡的最大泡半径、溃灭周期及泡能等特征参量的影响,结果表明壁面弹性模量的增大,将导致空泡最大泡半径、泡能和脉动周期等参量减小。本文的研究结果不仅有助于加深对空化、空蚀现象的认识,从而减轻和消除空化对船舶、水利、水电设施和机械造成的危害,同时也为提高激光加工、激光医疗的效率提供理论和实验依据。更多还原

【Abstract】 In this paper, the laser-induced bubble dynamics and bubble-collapse-induced liquid-jet are systemically investigated by numerical, theoretic and experimental analyses. Meanwhile, the effect of liquid viscosity, surface tension, temperature, gas content and the elastic modulus on bubble expansion and collapse are also performed.Firstly, based on the cavitation bubble dynamic theory, the relationships between each characteristic parameter are deduced and then an amended cavitation bubble dynamic model is provided. Employing the finite difference calculus, the behavior of the cavitation bubbles in liquids of different viscosity, surface tension, temperature, gas content and condensability are obtained. Meanwhile, the effects of liquid parameters on bubble radius, the velocity and the acceleration of the bubble wall, and the collapse time of the bubble are also analyzed. The numerical results show that liquid parameters have important effects on the expansion and collapse process of single bubble.Secondly, by the optical detection technique based on fiber-coupling beam deflection principle, the laser-induced plasma shock wave, laser-generated bubble and bubble-collapse-induced plasma shock wave are inveatigated by experiment during the high-power laser interacts with an underwater target. Then the dynamic behavior of a bubble in different liquids is systematically investigated. Quantitative relationships between liquid parameters, such as liquid viscosity, surface tension, temperature, and bubble characteristic parameters are also obatained. Good agreement has been established between numerical and experimental results. Moreover, from the modified Rayleigh theory, the liquid-jet velocity and corresponding liquid-jet impact pressure in different liquids can also be deduced. It is shown that the viscous force decreases bubble growth and collapse process, make it expand or collapse less violently. For a high viscosity, few liquid jets can impact the boundary and result in lower cavitation erosion. On the other hand, the surface-tension forces stave bubble growth progress and speed up bubble collapse process, so higher surface-tension increases liquid-jet impact force and produced higher erosive power. In addition, as the temperature of a liquid is one of the basic factors determining liquid viscosity, surface tension and the vapor pressure inside the bubble, it is an important factor determining cavitation and cavitation erosion.Based on the systematical investigation of cavitation bubble oscillation near different boundaries, the influence of the elastic modulus on the behavior of bubbles is obtained. Increasing elastic modulus leads to a significant decrease of bubble radius, collapse time and the bubble energy.These results are valuable in the fields of cavitation erosion, collateral damage in laser surgery, and cavitation-mediated enhancement of pulsed laser ablation of tissue; what is better, these results provide the theoretical and experimental reference to rational use of laser-induced plasma shock wave and cavitation, laser processing, laser lithotripsy, laser ophthalmology, and corresponding hydromechanics, etc.更多还原