Euler–Lagrange simulations of near-surface gas transport in vibrated bubbly flows

The downward rectified motion of gas in vibrated liquids, caused by compressibility–vibration coupling between bubbles and the surrounding fluid, is a phenomenon observed in experiments. The coalescence of injected gas can lead to the formation of gas-rich regions, which significantly alter the hydrodynamic damping properties of fluid–structure systems. Downward motion occurs when the primary Bjerknes force exceeds the buoyancy force, a condition only met when a bubble descends past a critical "neutral depth." However, experimental observations of bubbles crossing this depth are limited, and the mechanisms enabling this transport remain poorly understood. To address this gap, we present a numerical study using diffuse-interface and Euler–Lagrange models that incorporate radial bubble dynamics and two-way coupling with the liquid phase. The numerical results are validated against analytical predictions for isolated bubbles and then used to quantify bubble trajectories and forces during downward transport. Our findings suggest that vibration-induced liquid surface waves generate bulk fluid motion that drives bubbles past the neutral depth, revealing a mechanism for gas migration in vibrated multiphase systems.