PIV-Based Acoustic Pressure Measurements of a Single Bubble near the Elastic Boundary

Abstract

The objective of this paper was to investigate acoustic pressure waves and the transient flow structure emitted from the single bubble near an elastic boundary based on the particle image velocimetry (PIV). A combination of an electric-spark bubble generator and PIV were used to measure the temporal bubble shapes, transient flow structure, as well as the mid-span deflection of an elastic boundary. Results are presented for three different initial positions near an elastic boundary, which were compared with results obtained using a rigid boundary. A formula relating velocity and pressure was proposed to calculate the acoustic pressure contours surrounding a bubble based on the velocity field of the transient flow structure obtained using PIV. The results show the bubbles near the elastic boundary presented a “mushroom” bubble and an inverted cone bubble. Based on the PIV-measured acoustic pressure contours, a significant pressure difference is found between the elastic boundary and the underside of the bubble, which contributed to the formation of the “mushroom” bubble and inverted cone bubble. Furthermore, the bubbles had opposite migration direction near rigid and elastic boundaries, respectively. In detail, the bubble was repelled away from the elastic boundary and the bubble was attracted by the rigid boundary. The resultant force made up of a Bjerknes force and buoyancy force dominated the migration direction of the bubble.

Study on Non-Spherical Deformation Velocity of a Single Cavitation Bubble

“…Due to the characteristic of the elastic boundary, the bubble surface contraction velocity appeared different. The numerical results for a bubble near the elastic boundary using the fluid-structure interaction model have been carried out [26][27][28]. Convex and concave deformation of the elastic boundary occurs, and an annular liquid jet is formed during its collapsing stage, which is the reason for the special non-spherical shape.…”

Ice-Water-Gas Interaction during Icebreaking by an Airgun Bubble

“…These oscillatory pressure peaks Initially, when the compressed gas was released into water, an initial shock wave was generated immediately. The directional fast air jet pushes the water impacting on the wall continuously and rapidly, forming a transient vortex in front of the wall [38,39]. Under this water impact, several oscillatory pressure peaks were observed right after the initial shockwave, whose duration was around 1-2 ms.…”