Polar Patterns in Active Fluids

TL;DR

This paper investigates the complex spatio-temporal behaviors of polar active fluids, revealing transitions from uniform to chaotic states driven by activity levels and highlighting unique traveling wave phenomena distinct from nematic active fluids.

Contribution

It introduces a hydrodynamic model for polar active fluids, demonstrating novel behaviors and mapping the dynamics to a diffusion-reaction-convection system.

Findings

Transition from isotropic to polarized states with density

Unstable polarized states at high activity levels

Emergence of traveling bands, vortices, and chaos

Abstract

We study the spatio-temporal dynamics of a model of polar active fluid in two dimensions. The system exhibits a transition from an isotropic to a polarized state as a function of density. The uniform polarized state is, however, unstable above a critical value of activity. Upon increasing activity, the active fluids displays increasingly complex patterns, including traveling bands, traveling vortices and chaotic behavior. The advection arising from the particles self-propulsion and unique to polar fluids yields qualitatively new behavior as compared to that obtain in active nematic, with traveling-wave structures. We show that the nonlinear hydrodynamic equations can be mapped onto a simplified diffusion-reaction-convection model, highlighting the connection between the complex dynamics of active system and that of excitable systems.