Wake-induced lateral migration of approaching bubbles

•Two gravity-driven bubbles arranged in a line are computed.•The bubbles perform wake acceleration, lateral migration, and potential repulsion.•Lift reversal happens with the development of vorticity generation at bubble surface.•The relative motion of bubbles is connected with the vortex structure behind bubbles. In the motion of two gravity-driven bubbles arranged in a line, the trailing bubble is known to accelerate in the wake of the leading bubble. Furthermore, the approaching bubble migrates laterally as a result of bubble–bubble interactions. This paper presents the physical mechanisms for the acceleration and lateral motions of deformable bubbles under stable conditions, i.e., rectilinear motion in a solitary bubble, using numerical simulations. First, the trailing bubble decreases the drag coefficient relative to the case of a spherical bubble as a result of the increased vorticity generated at the leading bubble surface by its deformation. Second, the trailing bubble moves laterally as a result of the shear-induced lift force. In addition, lift reversal occurs in high Bond number cases and very weak lift occurs in low Galilei number cases. Predictions under the assumption of spherical bubbles nearly reproduce the interaction of a pair of deformable bubbles; however, the motion associated with the lift reversal cannot be predicted. Third, the bubbles repel each other as a result of their potential interaction when they are adjacent. This repulsive interaction is due to both the pressure at the surface and the vortex interaction around the bubbles.