Fragmentation in turbulence by small eddies

Area of Science:

• Fluid dynamics
• Turbulence research
• Multiphase flow

Background:

• The Kolmogorov-Hinze paradigm, established in the 1950s, is the classical model for bubble and drop fragmentation in turbulent flows.
• This paradigm assumes fragmentation is caused solely by eddies of similar size to the bubble/drop, despite turbulence encompassing a wide range of eddy scales.

Purpose of the Study:

• To experimentally challenge the classical hypothesis that bubbles are broken by same-scale eddies.
• To investigate the role of different eddy sizes in bubble fragmentation within turbulent environments.

Main Methods:

• Designed a novel experiment to isolate and control eddies of various sizes.
• Physically disentangled the influence of different eddy scales on bubble fragmentation.

Main Results:

• Provided experimental evidence that bubbles are preferentially broken by eddies smaller than the bubble itself (sub-bubble-scale eddies).
• Demonstrated that bubble fragmentation is not solely determined by stress or Weber number, but also by the interplay of different timescales.
• Observed that bubbles undergo rapid fragmentation via intense local deformation by small eddies, rather than slow elongation by same-scale flows.

Conclusions:

• The classical Kolmogorov-Hinze paradigm for bubble fragmentation in turbulence is incomplete.
• Sub-bubble-scale eddies play a critical role in bubble breakup.
• A more nuanced understanding of fragmentation dynamics, considering timescales and eddy-scale interactions, is required.