强激光水中诱导等离子体冲击波数值模拟

Numerical Simulation of High Intensity of Laser Induced Plasma Shock Wave in Water

在强激光与水介质作用过程中,等离子体和冲击波的形成机理是人们关心的主要问题之一。采用双脉冲激光纹影摄影法,获得了强激光作用时水中的冲击波流场图形,建立了激光与水作用两相流计算模型,建模时考虑了激光吸收,水体汽化、等离子体形成和膨胀等过程。对强激光作用水体形成冲击波的过程进行了数值模拟计算,获得了与实验相符的计算结果。进一步分析了激光诱导等离子体冲击波的传播特性,并与经典理论模型结果进行了比较。研究结果表明,在激光作用下,水中等离子体快速膨胀形成的冲击波传播初始速度高达上千米每秒,压力约为十几吉帕,随后冲击波的速度和压力迅速衰减,1 ms后衰减到声波速度。

Laser-induced plasma formation and shock wave generation mechanism are our concern problems in investigating high intensity laser pulse focusing into water. A high speed schlieren photography technique with double-pulse lasers is used as a background light source, and the temporal and spatial evolution of shock wave are obtained. A two- phase computation model is established in consideration of water vaporization, plasma absorption laser pulse energy. The processes of laser induced plasma shock wave in water are numerically simulated. A reasonable agreement is obtained between experimental and simulation results. The shock wave propagation characteristics are studied,and comparison between simulation results and theoretical predictions are presented. The results show that the shock wave speeds in the initial stages of laser induced breakdown in water is up to 5 km/s, and pressure is up to a dozen GPa. Shock wave velocity and pressure decay rapidly over time, which decrease to acoustic speed in an 1 ms later after breakdown.