Abstract
Contribution of a toroidal vortex behind a bubble to its steady drag was experimentally investigated. Bubble motion in eight different liquids were observed using high-speed photography. Photochromic dye was used to visualize the rear vortex structure. We clarified that the critical aspect ratio of bubble obtained previously in numerical simulations for the onset of the existence of the standing eddy and three-dimensional wake behind an oblate spheroid bubble corresponds well to our experimental results when the front aspect ratio is used. Non-dimensional steady drag on a bubble was found to have a linear relation with the front aspect ratio. It is also confirmed that the existence of standing eddy hardly changes the drag.
