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arXiv · 2202.06162

Formation and dynamics of a semi vortex ring connected to a free surface

Alexandre Vilquin·Samuel Hidalgo-Caballero·Vincent Pagneux·Agnès Maurel·Philippe Petitjeans
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Abstract

Playing a role in the locomotion of some animals such as the water strider, the formation and dynamics of a semi vortex ring connected to a free surface are experimentally investigated. This semi vortex ring is generated by the circular motion of a flat circular disk in water. Digital Particle Image Velocimetry provides velocity fields and vortex properties. We show how in a broad range of Reynolds numbers, the properties of the semi vortex rings are related to the disk characteristics. In particular, our results highlight a formation process more complex than for a complete vortex ring produced by a piston stroke. In addition to the classical rolling up at the rear of the disk, a shedding phenomenon occurs on the leading edge, producing secondary vortices. The Strouhal number related to this shedding process reveals that it comes from the free-shear instability of the boundary layer identified in the near wake of a cylinder by Bloor. Finally we show that the disk thickness affects the final properties of the semi vortex rings through emission frequency of secondary vortices.

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Alexandre Vilquin, Samuel Hidalgo-Caballero, Vincent Pagneux, Agnès Maurel, Philippe Petitjeans. 2022-02-12. Formation and dynamics of a semi vortex ring connected to a free surface. https://arxiv.org/abs/2202.06162

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