Model flocks in a steady vortical flow

TL;DR

This paper investigates how a steady vortical flow influences flocking behavior in a modified Vicsek model, revealing increased filamentarity and particle confinement effects due to external fluid motion.

Contribution

It introduces a distinction between intrinsic and extrinsic noise in flocking models and studies the impact of a vortical flow on flock morphology and dynamics.

Findings

Filamentarity of flock increases above a critical flow speed.

Particles tend to cluster in low vorticity regions due to flow effects.

The angle between flow and particle movement follows a power law distribution.

Abstract

We modify the standard Vicsek model to clearly distinguish between intrinsic noise due to imperfect alignment between organisms, and extrinsic noise due to fluid motion. We then consider the effect of a steady vortical flow, the Taylor Green vortex, on the dynamics of the flock, for various flow speeds, with a fixed intrinsic particle speed. We pay particular attention to the morphology of the flow, and quantify its filamentary. Strikingly, above a critical flow speed there is a pronounced increase in the filamentarity of the flock, when compared to the zero flow case. This is due to the fact that particles appear confined to areas of low vorticity; a familiar phenomena, commonly seen in the clustering of inertial particles in vortical flows. Hence the cooperative motion of the particles gives them an effective inertia, which is seen to have a profound effect on the morphology of the flock, in the presence of external fluid motion. Finally we investigate the angle between the flow and the particles direction of movement and find it follows a power law distribution.