Globally aligned states and hydrodynamic traffic jams in confined active suspensions

TL;DR

This paper explores how confined active liquids exhibit diverse hydrodynamic behaviors like density waves, vortices, and shocks, driven by particle shape and interactions, using simulations and theoretical models.

Contribution

It introduces a comprehensive analysis of phase behaviors in confined active suspensions, combining simulations with mean-field kinetic theory and traffic flow models.

Findings

Observation of coherent density waves and global alignment

Identification of stationary asters and vortices

Demonstration of density shocks and rarefaction waves

Abstract

Strongly confined active liquids are subject to unique hydrodynamic interactions due to momentum screening and lubricated friction by the confining walls. Using numerical simulations, we demonstrate that 2D dilute suspensions of fore-aft asymmetric polar swimmers in a Hele-Shaw geometry can exhibit a rich variety of novel phase behaviors depending on particle shape, including: coherent polarized density waves with global alignment, stationary asters, persistent counter-rotating vortices, density shocks and rarefaction waves. We also explain these phenomena using a linear stability analysis and a nonlinear traffic flow model, both derived from a mean-field kinetic theory.