Fragmentation in turbulence by small eddies*

From air-sea gas exchange, oil pollution, to bioreactors, the ubiquitous fragmentation of bubbles/drops in turbulence has been modeled by relying on the classical Kolmogorov-Hinze paradigm since the 1950s. This framework assumes that bubbles/drops are broken solely by eddies of the same size, even though turbulence is well known for its wide spectrum of eddy scales. Here, by designing a new experiment that can physically disentangle eddies of various sizes, we report an experimental work to challenge this assumption and show that bubbles are preferentially broken by sub-bubble scale eddies. Our work also highlights that fragmentation cannot be quantified solely by the stress criterion; The competition between different time scales is equally important. Instead of being elongated slowly and persistently by large-scale flows, bubbles are fragmented in turbulence by a burst of intense local deformation caused by small eddies that could release their energy within a short time.