Dynamics of an eccentric identical bubble pair in a quiescent liquid column

Bubble-induced turbulence and mixing has been identified as a prominent passive approach in enhancing heat and mass transfer associated with engineering applications. This study numerically analyzes buoyancy-driven interactions between initially eccentric bubble pairs in a quiescent liquid column. The effects of fluid parameters and initial eccentricity (ϵ*) on bubble hydrodynamics are examined. Using the volume-of-fluid method with a finite volume approach, the bubble–fluid interface is precisely captured, while the lateral migration of the trailing bubble (TB) relative to the leading bubble is quantified using Kirchhoff equations. The results suggest that the TB's lateral migration transitions from attraction with flatter ellipsoidal deformation to repulsion with a spherical shape as the Bond number (Bo) decreases from 4 to 1. An increase in the Galilei number (Ga) from 30 to 60 intensifies the wake effect, leading to quicker TB attraction. Streamwise vorticity (ωy) governs bubble motion through vortex structures, with Bo reducing wake range and strength, while Ga expands the wake and strengthens vortex-induced attraction. Drag reduction of TB is more evidently observed under attraction cases when the ϵ* decreases from 1.2 to 0.9 (30%), while under repulsion, it peaks when ϵ* decreases from 0.6 to 0.3 (20%). In terms of lift forces experienced by TB, CL increases by 261% under attraction as ϵ* increases from 0.3 to 1.2, but decreases by 50% under repulsion. Stagnation point shiftings at high Bo create distinct pressure coefficient (CP) profiles between attraction and repulsion, indicating that pressure asymmetry dominates attraction, while viscous asymmetry drives repulsion.