Clustering and surface distributions of buoyant particles in open-channel flows

TL;DR

This paper explores how buoyant particles cluster and distribute on the water surface in open-channel flows, highlighting the roles of capillary forces, flow dynamics, and secondary currents through experiments and theoretical extension.

Contribution

It introduces a dimensionless clustering Weber number (We_cl) to extend capillary clustering theory to open-channel flows and emphasizes the influence of secondary currents on particle distribution.

Findings

Clustering behavior varies with particle size and density.

The clustering Weber number (We_cl) effectively predicts clustering regimes.

Secondary currents significantly influence lateral particle distribution.

Abstract

This study investigates the clustering behaviour and surface distributions of buoyant particles at the air-water interface in open-channel turbulent flow, focusing on the interplay between capillary attraction, hydrodynamic drag, and flow-driven lateral transport. Using controlled laboratory flume experiments, we systematically examine clustering dynamics for two particle types differing in size and density. To interpret the observed behaviour, we extend capillary-based clustering frameworks to open-channel flows by introducing a dimensionless clustering Weber number (We_cl) that captures the balance between the flow-induced disruptive force and capillary attraction, providing a compact description of the observed clustering behaviour. In addition, we demonstrate that secondary currents play a central role in surface particle transport, producing systematic lateral accumulation that depends on channel aspect ratio. Together, these findings extend capillary-driven clustering theory to open-channel turbulence and reveal secondary currents as a key mechanism controlling particle surface distributions.