水下冲击波聚焦作用下空化效应的实验研究

冲击波聚焦在聚焦区域形成局部较高压力的同时还会在焦区产生空化效应。基于旋转椭球面反射罩及置于其焦点的水中脉冲放电声源建立了水下冲击波聚焦系统。通过压力传感器测量了反射罩轴向的压力历程曲线及峰值压力分布。同时，搭建了高速摄影所需的光学装置，拍摄了空化现象的高速摄影图片，对水下冲击波聚焦过程和空化汽泡的产生、发展及湮灭的整个过程进行了研究。对压力历程曲线和高速摄影所得结果进行对比分析得到空化现象产生的物理过程。实验结果表明：负压是空化现象发生的主要原因，空化汽泡的塌缩时间与汽泡半径存在线性关系，并且汽泡膨胀阶段持续的时间大于塌缩阶段持续的时间。

Experimental study on the cavitation phenomena induced by underwater shock wave focusing

Shock wave focusing can generate extremely high pressure in a narrow region, in which the cavitation phenomena may successively occur. An underwater shock wave focusing sys- tem was set up based on the focusing characteristics of an ellipsoidal reflector with a pulsed dis- charge point sound source located at one of the focus. The pressure-time history and the peak pressure along the axial position were measured by under-water pressure sensors. At the same time, an optical arrangement was set up for obtaining the high speed photographs of cavitation. The cavitation process and related characteristics induced by shock wave focusing were studied by experiments, including the generation, growth and collapse of cavitation bubbles. By combined a- nalysis of the measured pressure histories and the optical photographs, we concluded that the negative pressure is the main cause of cavitation phenomena. There is a linear relationship be- tween the maximum bubble radius and the time to collapse, and the growth time of bubble is lon- ger than the decay time.