Chirality transitions in a system of active flat spinners

TL;DR

This study investigates how active flat spinners exhibit chirality transitions in a 2D fluidized system, revealing complex flow behaviors and the influence of particle velocity correlations on flow chirality.

Contribution

It uncovers the phenomenon of chirality transitions in active rotors and links these to statistical correlations between particle spin and velocity, a novel insight.

Findings

Chiral flow can switch sign with increased energy input.

Complex vortex structures with multiple persistent vortices are observed.

Flow chirality is governed by correlations between particle spin and translational velocity.

Abstract

We study in this work the 2D dynamics of an experimental system of disk-shaped rotors, fluidized by turbulent upflow. Contrary to previous knowledge, our experiments show the same particle chiral geometry can produce flows with different chiralities. In particular, we unveil a conspicuous complex chiral flow, which displays multiple persistent vortexes with either sign, located randomly in the system. This peculiar phase mediates a continuous transition, which takes place as the kinetic energy input increases, from a flow with positive chirality (one vortex rotating in the same direction as particles spin) to a flow with negative chirality (one vortex in opposite sense to particle spin). We find that these surprising transitions are determined by the specific state of the statistical correlations between particle spin and translational velocity. We discuss how these correlations are determined in turn by the combined action of a series of mechanisms (for instance, heat dissipation at the boundaries, particle activity, average kinetic energy...), several of which are unveiled here.