Improved instruments and methods for the photographic study of spark-induced cavitation bubbles

Abstract

An underwater spark is able to induce a cavitation bubble, and this principle has been utilized to make cavitation bubble generators for several decades. In this paper, an improved instrument for generating spark-induced cavitation bubbles is described in detail. The voltage time history inside the instrument is measured to show the working process and principle. Cavitation bubbles are generated by the instrument and recorded by a high-speed camera. The radius time history of the bubble is obtained using an image processing algorithm. The ratio of its minimum radius to its maximum radius reaches ~0.2, which indicates that there is little undissolved gas in the bubble. With the radius time history, the velocity fields around the bubbles were calculated by the 1D continuity flow equation, and the pressure fields were calculated by the 1D Euler equation. One cavitation bubble is chosen and discussed in detail. The velocity and pressure on the bubble interface achieve their maximums (~25 m/s and ~1.2 MPa, respectively) at the same time, when the radius is at its minimum (~1 mm). Some statistical results are also presented to show the effect of the instrument.