Swarming bubbles stir and spread

Abstract

A Lagrangian description of bubble swarms has largely eluded both experimental and numerical efforts. Now, in a tour de force of deep-learning-enabled optical tracking measurements, Huang et al. (2025 J. Fluid. Mech. 1014, R1) have managed to follow the three-dimensional trajectories of 105 deforming and overlapping bubbles within a swarm, perhaps for long enough to witness their approach to the diffusive limit. Their results reveal that bubble swarms exhibit a dispersion law strikingly reminiscent of classical Taylor dispersion in isotropic turbulence, but with an earlier, undulatory transition from the ballistic-to-diffusive regime. Huang et al. (2025 J. Fluid Mech. 1014, R1), have helped close the loop on our understanding of Lagrangian bubble dispersion – from self-stirring swarms to bubbles in isotropic turbulence.