Chiral active systems near a substrate: Emergent damping length controlled by fluid friction

TL;DR

This paper introduces a particle-based hydrodynamic simulation method to model friction effects near a substrate in chiral active fluids, revealing a damping length that controls vortex size and system behavior, aligning well with experimental observations.

Contribution

The authors develop a novel simulation approach that links friction coefficients to system parameters, enabling prediction of vortex size and other properties in quasi-two-dimensional active fluids.

Findings

Damping length limits vortex size in active fluids.

Simulation results agree with experimental data.

Friction influences energy spectra and rotational diffusion.

Abstract

Chiral active fluids show the emergence of a turbulent behavior characterized by multiple dynamic vortices whose maximum size is specific for each experimental system. This is in contrast to hydrodynamic simulations in which the size of vortices is only limited by the system size. We propose and develop an approach to model the effect of friction close to a surface in a particle based hydrodynamic simulation method in two dimensions, in which the friction coefficient can be related to the system parameters and to the emergence of a damping length. This length limits the size of the emergent vortices, and influences other relevant system properties such as the actuated velocity, rotational diffusion, or the cutoff of the energy spectra. Comparison of simulation and experimental results show a good agreement which demonstrates the predictive capabilities of the approach, which can be applied to a wider class of quasi-two-dimensional systems with friction.