Trapping of heavy flexible discs in a vortical flow*

During the course of experiments in a water tank, thin heavy flexible silicone discs are surprisingly observed orbiting at a quasi-stable radial position from the axis of a strong vortex. Given that the discs are denser than the fluid, their persistent orbit around the vortex is notable because it would have been expected that the discs, similarly to other types of particles, would be centrifuged away from the vortex core. To investigate this curiosity, referred to as a trapping event, a process was developed to obtain the 3D reconstruction of the thin flexible discs in the flow. It is observed that the discs’ physical properties in relation to the vortex strength (Re_Γ ∼ 10⁵) are linked to the radial positions of the discs’ orbit. The 3D reconstruction process and theoretical approaches to understanding the mechanism behind the trapping event will be discussed.