《01 A High-Speed Photographic Study of Ultrasonic Cavitation Near Rigid Boundary》.pdfVIP

637 2008,20(5):637-644 A HIGH-SPEED PHOTOGRAPHIC STUDY OF ULTRASONIC * CAVITATION NEAR RIGID BOUNDARY BAI Li-xin, XU Wei-lin, TIAN Zhong, LI Nai-wen State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu 610065, China, E-mail: lixin.bai@ (Received January 18, 2008, Revised April 17, 2008) Abstract: This article investigated an existing steady pattern of collapse and rebound (disintegration and aggregation) of cavitation bubbles near rigid boundary in acoustic field. A deformation process of cavitation bubble was accomplished in two acoustic cycles, namely, a spherical bubble collapsed towards the boundary to its minimum volume and then rebounded and grew into a toroidal bubble (or two individual bubbles) in one acoustic cycle, and the toroidal bubble (or two individual bubbles) collapsed towards the center of ring to its minimum volume, and then rebounded into a spherical bubble in the next acoustic cycle. Inertia force plays a key role in the transition between these two states. The microjet produced during the collapse of spherical bubble and the shock wave produced during the collapse of toroidal bubble (or two individual bubbles) impacts the boundary alternately. A cavitation bubble operating in this pattern can thus be an effective corrosion mechanism of rigid boundary. Key words: cavity, ultrasonic cavitation, high-speed photography, visualization 1. Introduction Rayleigh[1] considered the collapse of an isolated Cavitaion refers to the formation and subsequent spherical cavity in a liquid under hydrostatic pressure. dynamic life of bubbles in liquids subjected to a Assuming incompressible and inviscid behaviour of sufficiently low pressure.