Experimental Research on the Influence of Different Curved Rigid Boundaries on Electric Spark Bubbles.

Chunlong Ma,Mengnan Wang,Dongyan Shi,Xiongwei Cui,Yingyu Chen

doi:10.3390/ma13183941

Abstract

It is well known that the bubble dynamics and load characteristics of cavitation bubbles depend to a great extent on their proximity to the boundary. The purpose of this study is to explore the relationship between the boundary curvature and bubble dynamics, as well as the load characteristics, and summarize the relevant change laws. This study takes three hemispheres of different curvatures and one flat board as its main research boundaries. The hemisphere was chosen as the curved surface boundary because the hemisphere represents the simplest type of curved surface boundary. This method allowed us to easily observe the experimental results and summarize the change laws of bubble dynamics and load characteristics. A high voltage electricity of 400 V was used to produce stable and repeatable electric spark bubbles in this experiment. Since the pulsation time of the bubbles is very short, we used a high-speed camera to acquire the necessary photographs. We also used a Hopkinson bar (HPB) to measure the bubble collapse load. Suppose that the dimensionless parameter of curvature is ζ and the dimensionless parameter of the explosion distance is γ. By summarizing the 44 groups of the experimental results under different combinations of ζ and γ, we found that the cavitation bubble dynamics and loading characteristics are affected by ζ. With an increase of ζ, the shockwave load and bubble collapse load will decrease. In addition, in terms of load characteristics, this study further verified the change trend of the shockwave load and bubble collapse load with γ. For the bubble shrink shape, this paper illustrates the relationship between the bubble’s shrink shape and its shrinkage speed. Four typical bubble shrink shapes are summarized. The effects of different ζ and γ values on the jet are preliminarily explored using the experimental results, and, by considering the experimental results, the developmental trends of the time of the bubble’s first pulsation period are discussed.

Highlights

Bubbles’ pulsation characteristics near object surfaces are widely studied in many fields, such as underwater explosions [1,2], damage to propellers by cavitation bubbles [3,4], ultrasonic cleaning [5,6], medical treatment [7], etc
The experimental results show that different ζ and γ values will affect the bubble dynamics and experimental results that different ζ and γ values will of affect the bubble and load The characteristics
= 0.83, here, when the bubble formed an upward jet in the first stage, the bottom of the bubble was Through measurements and calculations, we found that when ζ = 0, in the first pulsation phase, Vx(0/0.83) = 13.98 mm/ms and V y(0/0.83) = 21.12 mm/ms (see Figure 11b (1)); when ζ = 0.4, in the first pulsation phase, Vx(0.4/0.83) = 2.13 mm/ms and V y(0.4/0.83) = 20.59 mm/ms (see Figure 11b (2)); when ζ = 0.6, in the first pulsation phase, Vx(0.6/0.83) = 5.97 mm/ms and V y(0.6/0.83) = 18.27 mm/ms (see Figure 11b (3)); and when ζ = 1.2, in the first pulsation phase, Vx(1.2/0.83) = 6.91 mm/ms and

Summary

Introduction

Bubbles’ pulsation characteristics near object surfaces are widely studied in many fields, such as underwater explosions [1,2], damage to propellers by cavitation bubbles [3,4], ultrasonic cleaning [5,6], medical treatment [7], etc. Many previous studies proved that boundary conditions (such as fixed boundaries [8,9,10], free surfaces [11,12,13], elastic boundaries [13], and motion boundaries [14]) greatly affect the bubbles’ pulsation characteristics. Under the influence of a fixed boundary, a bubble will form a jet directed at the fixed boundary and a Materials 2020, 13, 3941; doi:10.3390/ma13183941 www.mdpi.com/journal/materials. Materials 2020, 13, 3941 local high pressure region during the contraction phase; the formed jet load will directly act on the fixed boundary. In the study of Tomita et al [16], the characteristics of bubble dynamics under the influence of a curved surface boundary are given from theoretical and experimental perspectives

Objectives

Methods

Results