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Study on Cavitation Generation and Acoustic Transient in Liquid Nitrogen

液氮空化产生及声瞬变研究

基本信息

批准号：
06650185
负责人：
TOMITA Yukio
金额：
$ 1.47万
依托单位：
Hokkaido University of Education
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-06650185/
关键词：
Cavitation Bubble Liquid Nitrogen Acoustic Transient Shock Wave Laser Plasma Phase Ghange 過度音響

项目摘要

A single bubble was produced by focusing a pulsed ruby laser into subcooled liquid nitrogen at various applied pressures. Highly spherical cavitation bubbles were successfully generated by using an annular laser beam adjusted through a double-stage lens array. When the laser energy exceeds a threshold energy, the optical breakdown takes place, following by a series of high-speed phenomena such as the plasma formation, acoustic transients including shock wave emission and vapor bubble generation. The dynamics of these phenomena, especially the initial behavior and subsequent motion of the bubbles, are investigated by means of high speed photography. It is found that very weak pressure dependency is found for the threshold conditions of bubble generation. On the other hands, it is also a bubble is generated strongly reflecting from the plasma formation which occurs along with the optical axis. Therefore initial bubble shape is nonspherical, but its volume varies similarly with time for different input energies. The liquid inertia is dominant during the bubble growth, whereas the thermal effect becomes significant in the collapse process, yielding the retardation of the bubble motion. The latter feature is primarily associated with the saturated vapor pressure inside a bubble and influenced by other thermodynamic effects which is confirmed by investigating the period of the bubble motion. A considerable instability takes place over the bubble surface immediately after the bubble rebound, mainly due to the Taylor instability coupled with thermal instability.

在不同的施加压力下，将脉冲红宝石激光聚焦到过冷的液氮中，产生了一个气泡。通过双级透镜阵列调节环形激光束，成功地产生了高度球形的空化气泡。当激光能量超过阈值能量时，发生光击穿，随后发生一系列高速现象，如等离子体的形成、包括激波发射在内的声瞬态和蒸汽泡的产生。这些现象的动力学，特别是气泡的初始行为和随后的运动，用高速摄影的方法进行了研究。发现气泡产生的阈值条件对压力的依赖性非常弱。另一方面，它也是由沿光轴发生的等离子体形成强烈反射而产生的气泡。因此，初始气泡形状为非球形，但在不同的输入能量下，其体积随时间的变化相似。在气泡生长过程中，液体惯性占主导地位，而在气泡坍塌过程中，热效应变得明显，导致气泡运动的迟滞。后一种特征主要与气泡内的饱和蒸汽压有关，并受到其他热力学效应的影响，这一点通过研究气泡运动周期得到证实。气泡反弹后，气泡表面立即发生了相当大的不稳定性，主要是由于泰勒不稳定性和热不稳定性的耦合。