Deformation and breakup of bubbles in turbulence

The breakup of bubbles in turbulence is a fundamental problem for many industrial processes, environmental flows, and fluid dynamics research, where the bubble population regulates the transport phenomena. Resolving the bubble population equation requires closure models for both the breakup frequency and the resulting daughter bubble size distribution. Despite extensive research on the topic, the developed models diverge substantially, and many questions remain on the mechanisms governing the interface evolution until breakup. To investigate this problem, we use five high-speed cameras to reconstruct the breakup process of air bubbles dispersed in homogeneous isotropic turbulence. These reconstructions are coupled with velocity measurements of the surrounding fluid using 3D Lagrangian particle tracking velocimetry (Shake-The-Box), which is then converted to a Cartesian grid using the VIC# (Vortex-in-cell) technique. We can reconstruct sub-bubble-scale eddies in the bubble vicinity with a resolution of 12η (equivalent to 0.1 times the average bubble diameter). Comparing the spatial and temporal scales of the local flow structures with those of the interface deformation, we observe that the mean squared stretching of bubbles grows ballistically (∝ τ²) during the breakup, mirroring the behavior of particle-pair dispersion for times shorter than one eddy turnover. Furthermore, we describe the different types of eddy-bubble interaction identified and their imprint on the fragmentation process. The experiments provide new insights that can be used to refine models of breakup frequency and daughter bubble size distribution.