Interaction Between an Oscillating Bubble and a Free Surface

Abstract

Interaction between a collapsing bubble and a free surface is investigated theoretically and experimentally using high speed photography. A limit value for the distance from the free surface to the center of the bubble reported to its radius is found. Under this limit the free surface is not disturbed before the end of the collapse in the first approximation. Only in this case, the method of images can be used and the free surface be replaced by an image-source, symmetrical with respect to the free surface, to the sink representing the bubble. Above this limit, precise measurements of bubble deformation and motion are given. Just after the collapse of the bubble begins, observations show a singular perturbation on the free surface, with the formation of a thin spike directed towards the air. In all cases, buoyancy has no time to take effect, and the bubble is repelled from the free surface while the re-entering jet, formed during collapse, is oriented away from it.