A body immersed in a supersaturated fluid like carbonated water can accumulate a dynamic field of bubbles upon its surface. The bubbles grow and coalesce as gas is continually pulled from the environment. If the body is mobile, the attached bubbles can lift it upward against gravity, but arrival at a free surface can clean the body of these lifting agents and the body may plummet. The process then begins anew, and continues for as long as the concentration of gas in the fluid supports it. In this work, experiments using fixed and free immersed bodies reveal fundamental features of force development. A continuum model which incorporates the dynamics of a surface buoyancy field is used to predict the ranges of body mass and size, and fluid properties, for which the system is most dynamic, and those for which body excursions are suppressed. And simulations are used to probe systems which are dominated by a small number of large bubbles. Body rotations at the surface are found to be critical for driving periodic vertical motions of large bodies, which in turn can produce body wobbling, rolling, and damped surface 'bouncing' dynamics. The body affects the environment as well, modifying gas transport, as evidenced by a much longer fluid degassing time when the body is present.
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S. E. Spagnolie, S. Christianson and C. Grote, Dancing raisins: levitation and dynamics of bodies in supersaturated fluids (submitted, 2023)
Many fundamental questions remain unanswered about the sedimentation of bodies in viscous fluids. For instance, even the dynamics of a single flexible filament have only recently been analyzed, and the interactions of viscous and elastic stresses can lead to slow shape changes or rapid buckling dynamics, as characterized by a dimensionless elasto-gravitation number. The dynamics of suspensions of flexible bodies has only just begun to receive mathematical attention, and even then only for weakly flexible filaments. Even two rigid sedimenting particles can undergo complex periodic sedimentation dynamics, so the general case is far from being completely characterized. The dynamics of flexible bodies in viscous flows remains both beautiful and analytically challenging, and is a topic of considerable practical interest.
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