超声空化及其声流结构实验研究*

超声空化及其声流效应在医学、化工和能源等领域得到广泛应用。本文采用高速摄像和粒子图像测速系统分别研究了超声场下的空化形态和声流场结构的时空演化规律。实验研究了50W，100W，200W和250W等四种不同输入功率对18kHz的超声变幅杆附近空化及其声流场的影响。研究结果表明：（1）在变幅杆下端面处观察到由大量空化气泡均匀分布组成的倒置锥形空泡结构，并且锥形空泡结构为稳态流动结构。（2）在超声变幅杆附近产生了两种不同的声流形式，第一种是变幅杆底端的射流型声流，第二种是变幅杆两侧的回旋流。此外，通过研究空泡与声流场中最大速度点之间的空间对应关系，发现声流是因为空泡流动带动而产生的。（3）空间位置和输入功率能显著影响射流型声流的流场结构，但是对回旋流的影响十分微弱。

Experimental study on ultrasonic cavitation and acoustic streaming structure

Ultrasonic cavitation and its acoustic streaming effect are widely used in medicine, chemical industry, energy fields. In this paper, the spatiotemporal evolution of cavitation and acoustic streaming field in ultrasonic field is studied by using high-speed camera and particle image velocimetry system. The effects of four different input powers (50W, 100W, 200W and 250W) on cavitation and acoustic flow field around 18 kHz ultrasonic horn were studied. The results show that: (1) the inverted conical bubble structure composed of many cavitation bubbles is observed at the lower end of the horn, and the conical bubble structure is a steady flow structure. (2) There are two different types of acoustic streaming near the ultrasonic horn, namely, acoustic jet streaming at the bottom of the horn, and the recirculation flow on both sides of the horn. In addition, by studying the spatial correspondence between the cavitation and the maximum velocity point in the acoustic flow field, it is found that the acoustic flow is driven by the cavitation flow. (3) The spatial position and input power can significantly affect the acoustic jet streaming, but the effect on the recirculation flow is very weak.