Flow Pattern and Vorticity Distributions around a Spherical-Cap Gas Bubble

Abstract

Velocity distributions, streamlines, vorticity distributions and stress distributions around a spherical-cap gas bubble were measured by use of the flow visualization method. A solid model of the same shape as the bubble was also used for comparison with the bubble. The solid model was pulled upward in a still liquid at the same speed as the bubble rose. To visualize the flow pattern, the trajectories of fine tracer bubbles mixed in a liquid phase were photographed by using a 35 mm camera equipped to move simultaneously with the bubble and the solid model. The obstacles observed in our experiment were always accompanied by a fully developed toroidal vortex.
Consequently, the following results were obtained.
(1) The bubble surface shows a tendency of free surface.
(2) High density of vorticities is observed in the vicinity of bubble edge.
(3) The streamline separates at the lower side of bubble edge.
(4) The separation point on the bubble surface coincides with the stagnation point.
(5) The separation point approaches the bubble edge as the curvature radius of bubble edge becomes small.
Furthermore, the flow mechanism around the bubble is discussed on the basis of these experimental results.