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Effect of plastron deformation on the wake of super-hydrophobic spheres

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This presentation is dedicated to the experimental investigation of the wake of free falling super-hydrophobic spheres within the so-called sub-critical regime. It is found that the air plastron adapts its shape to the flow-induced stresses, which compete with the surface tension. The study of the falling motion reveals that the plastron compliance has a sizeable influence on the wake development. Investigating the lift force experienced by the super-hydrophobic spheres, the onset of wake instabilities is found to be triggered earlier than for smooth spheres used as reference. Surprisingly, it is also observed that the early promotion of the wake instabilities is even more pronounced beyond a critical Weber number, which corresponds to a critical aspect ratio of the plastron. Furthermore, the magnitude of the hydrodynamic loads is found to be dependent on the average deformation of the gas/liquid interface. Indeed, in comparison to the reference spheres, high plastron deformation leads to lift and drag increase, whereas low plastron deformation yields lift and drag mitigation. Accordingly, taking into account the plastron deformation provides an attractive way to explain the somehow discordant results reported in other studies at comparable Reynolds numbers. The presentation will then focus on preliminary results over a broader range of Reynolds.

This talk is part of the Fluids Group Seminar (CUED) series.

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