Turbulent-like flows in quasi two-dimensional dense suspensions of motile colloids

TL;DR

This study models and experimentally investigates turbulent-like flows in dense suspensions of motile colloids driven by Quincke instability, revealing energy spectrum scaling and dynamic memory effects in quasi-two-dimensional conditions.

Contribution

It introduces a new experimental model using Quincke-driven colloids to mimic bacterial turbulence and analyzes flow dynamics and energy spectra in dense suspensions.

Findings

Energy spectrum scales as k^{-4} at high wavenumbers

Flow exhibits rapid velocity correlation decay within a cycle

Anti-correlation indicates dynamic structural memory

Abstract

Dense bacterial suspensions exhibit turbulent-like flows at low Reynolds numbers, driven by the activity of the microswimmers. In this study, we develop a model system to examine these dynamics using motile colloids that mimic bacterial locomotion. The colloids are powered by the Quincke instability, which causes them to spontaneously roll in a random-walk pattern when exposed to a square-wave electric field. We experimentally investigate the flow dynamics in dense suspensions of these Quincke random walkers under quasi two-dimensional conditions, where the particle size is comparable to the gap between the electrodes. Our results reveal an energy spectrum scaling at high wavenumbers as $ \sim k^{-4}$, which holds across a broad range of activity levels -- controlled by the field strength -- and particle concentrations. We observe that velocity time correlations decay within a single period of the square-wave field, yet an anti-correlation appears between successive field applications, indicative of a dynamic structural memory of the ensemble.