Laboratory Experiments on Rigid Particle Accumulation in an Ekman-driven Can Flow

In the Maxey-Riley regime, rigid particles have the propensity for accumulation around certain flow features. Recently, Rypina et al 2024 investigate this phenomenon for small buoyant spherical particles inside an analytical phenomenological analogue of a three-dimensional, Ekman-driven eddy flow, and observed particle accumulation around limit cycles close to the corresponding periodic orbits of fluid parcels. They also present simple theoretical arguments based on vorticity—strain considerations for why this attraction occurs. Motivated by an interest in observing this accumulation phenomenon firsthand, we conducted laboratory experiments seeding buoyant spherical particles within a cylindrical tank full of glycerin forced by a rotating lid. Experiments were carried out in an axially symmetric cylinder flow, as well as in a non-symmetric configuration with tilted lid. Preliminary findings indicate the existence of a central region where particles are retained and accumulating within for over a week, and an outer region spanning the periphery and central axis that becomes rapidly devoid of particles. We compare our observations with a numerical model of the can flow, and provide estimates of the particle accumulation rate within the can interior.