Role of sub-bubble eddies and capillary events in bubble breakup: an experimental investigation with 3D time-resolved measurements

The breakup of bubbles and droplets in turbulent flows is a fundamental phenomenon with wide-ranging applications in industrial processes, environmental sciences, and fluid dynamics research. Numerous open questions remain, particularly regarding the mechanics governing the interface evolution until breakup, a process that is still largely hidden and poorly understood. Specifically, the role of continuous phase turbulence compared to internal instabilities and capillary events during various phases of deformation is an underexplored issue, especially given the large separation of scales between the initial cavity and the Hinze scale. Additionally, the density and viscosity ratios between the discrete and continuous phases significantly alter the deformation and fragmentation processes.

Five high-speed cameras are used to reconstruct the breakup process of air bubbles and oil droplets in homogeneous isotropic turbulent environments. These reconstructions are coupled with velocity measurements of the surrounding fluid using 3D particle tracking velocimetry (shake-the-box). This technique allows us to reconstruct the sub-bubble eddy around the bubble. The spatial and temporal scales of the local flow structures are compared with the scales of the interface deformation. As a result, it is possible to isolate the deformation and breakup driven by turbulence from the fragmentation driven by capillary events, and to observe how the different topologies change with the density and viscosity ratios.