Three-dimensional analysis of the rising dynamics of individual ellipsoidal bubbles in an inclined column

Abstract

In this study, the dynamics of a single ellipsoidal air bubble rising in an inclined cylindrical vessel is experimentally investigated. The three-dimensional bubble trajectory reconstruction shows that the spirally rising bubble maintains two out-of-phase modes of oscillations, while the zigzagging bubble maintains a two-dimensional motion, despite the irregular rebounds with small amplitude. Assessing the bubble-wall rebounds for the helicoidal rising bubble shows that the normal restitution coefficient correlates with a modified normal Stokes number in the same manner as the normal wall collisions of liquid droplets [Legendre et al., 2005, Physics of Fluids 17, 097105]. A similar contribution of normal-to-wall and tangent-to-wall components of the kinetic energy in helicoidal bubble rise is maintained up to the highest inclination angle, i.e. 15°. However, for the zigzag rising bubble, despite the bubble rebounds on the wall, the wall-normal contribution of the kinetic energy is much less than its tangent-to-wall component.