Pair Dispersion of Bubbles in Isotropic Turbulence

Turbulence serves as a catalyst for rapid bubble dispersion, increasing the residence time of bubbles in the ocean and shaping the crucial process of mass transfer during air-sea interactions. In this Letter, we experimentally investigate the pair dispersion of bubbles in turbulence. Our findings highlight two key differences: initially, bubbles are preferentially drawn toward each other when in close proximity, which slows down their dispersion. As bubbles are driven further apart, they enter a superdiffusive regime where the Richardson constant is governed by two competing mechanisms: larger bubbles gain more kinetic energy due to biased sampling, yet simultaneously exhibit increased misalignment between their relative velocity and separation vector due to the inertia of bubbles, which limits the effectiveness of that energy in driving dispersion. These effects, absent in the tracer limit, offset each other, yielding a reduced yet size-independent Richardson constant. A model is then developed to predict this alignment behavior and the Richardson constant, providing a framework for the dispersion and transport of buoyant particles in turbulent flows.