Experimental Research on the Electric Spark Bubble Load Characteristics under the Oblique 45 Degree Curved Surface Boundary

In order to study the influence of the pressure load generated during the pulsation of cavitation bubbles on the oblique 45-degree curved surface boundary. The curved surface boundaries have different curvatures. This study also designs a multi-angle bracket to make the oblique boundary oblique 45 degrees. This research uses high-voltage electric discharge to generate electric spark bubbles, which act as cavitation bubbles. When the explosion source is at different distances from the oblique 45-degree boundary, a high-speed camera is used to capture the pulsation process of electric spark bubbles. A pressure sensor is used to measure the pulsating load of the electric spark bubbles on the oblique 45-degree boundary during the pulsation process. In this study, we use the dimensionless parameter ζ to represent the curvature of the oblique 45-degree boundary. The dimensionless parameter γ is used to represent the shortest distance between the explosion source and the oblique 45-degree boundary. It is found through experiments that the oscillation characteristics and pulsating load of electric spark bubbles will be affected by ζ and γ. This study summarized six types of unique bubble pulse shapes from 44 groups of experiments. They are “mushroom shape without jet”, “mound shape with jet”, “jellyfish shape with jet”, “oval shape with jet”, “drop shape without jet”, and “spherical shape without jet”. In this paper, the ABAQUS/Explicit is used to simulate the ring-shaped bubble that is not clearly captured by the high-speed camera. Finally, the study summarizes the shock wave load generated during the explosion, the first pulsation load, and the second pulsation load of electric spark bubbles, and finds an obvious overall trend of change.

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

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.