Asymmetry of motion: vortex rings crossing a density gradient. (10th April 2023)

• Record Type: Journal Article
• Authors: Su, Yunxing; Wilhelmus, Monica M.; Zenit, Roberto
• Is Part Of: Journal of fluid mechanics. Volume 960(2023)
• Publication Date: 2023-04-10
• Subjects: vortex dynamics -- vortex instability; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2023.165
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract: Abstract : Vortex rings are critical for thrust production underwater. In the ocean, self-propelled mesozooplankton generate vortices while swimming within a weakly stratified fluid. While large-scale biogenic transport has been observed during vertical migration in the wild and lab experiments, little focus has been given to the evolution of induced vortex rings as a function of their propagation direction relative to the density gradient. In this study, the evolution of an isolated vortex ring crossing the interface of a stable two-layer system is examined as a function of its translation direction with respect to gravity. The vortex ring size and position are visualized using planar laser-induced fluorescence (PLIF) and the induced vorticity field derived from particle image velocimetry (PIV) is examined. It is found that the production of baroclinic vorticity significantly affects the propagation of vortex rings crossing the density interface. As a result, any expected symmetry between vortex rings travelling from dense to light fluids and from light to dense fluids breaks down. In turn, the maximum penetration depth of the vortex ring occurs in the case in which the vortex propagates against the density gradient due to the misalignment of the pressure and density gradients. Our results have far-reaching implications for the characterization of local ecosystems in marine environments.