In most practical situations, cavitation bubbles do not occur in isolation but coexist with air bubbles in a large number. In gaseous water or in aerated water, there is no clear delimitation among vaporous cavitation bubbles, gaseous cavitation bubbles, swell-shrink air bubbles and stationary air bubbles. These kinds of bubbles influence one another. It is important to understand the mechanics of the interaction among these bubbles especially between two cavitation bubbles, between a cavitation bubble and an air bubble and between bubbles and boundary. There are a great number of theoretical or numerical studies of cavitation bubbles.

So XU Weilin and ZHANG Faxing of State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University and BAI Lixin of Institute of Acoustics, Chinese Academy of Sciences carried out an experimental study of the interaction of a cavitation bubble and an air bubble with a rigid boundary in various configurations (bubble-bubble-boundary interaction).

In the experiment, the researchers study the motion of a spark-induced cavitation bubble and an air bubble near a rigid boundary by using high-speed photography. Several dimensionless parameters are used to describe the geometrical configuration of the bubble-bubble-boundary interaction. The bubble-bubble interaction can be considered in two different conditions. The cavitation bubble will collapse towards the air bubble if the air bubble is relatively small, and away from the air bubble if the air bubble is relatively large. The two zones are identified in the bubble-boundary interaction, and they are the danger zone and the safety zone.

The relative position, the bubble-boundary distance and the bubble-bubble distance play important roles in the bubble-bubble-boundary interaction, which can be considered in several conditions according to the responses of the bubbles. Air jets are found to penetrate into the cavitation bubbles. The cavitation bubble and the air bubble (air jet) move in their own way without mixing. The motion of a cavitation bubble may be influenced by an air bubble and/or a rigid boundary. The influence of the air bubble and the influence of the boundary may be combined, like some thing of a vector.

This research result was published on the recently issued journal of JOURNAL of HYDRODYNAMICS (2010, 22(4): 503-512).