Model flocks in a steady vortical flow.

Area of Science:

• Collective behavior
• Non-equilibrium statistical mechanics
• Fluid dynamics

Background:

• The Vicsek model describes self-propelled particles with alignment interactions.
• Distinguishing intrinsic noise (imperfect alignment) from extrinsic noise (fluid motion) is crucial.
• Vortical flows can significantly alter particle dynamics and collective phenomena.

Purpose of the Study:

• To investigate the impact of a steady vortical flow (Taylor-Green vortex) on the Vicsek model.
• To analyze how flow speed influences flock morphology and filamentarity.
• To understand the role of effective inertia in particle clustering within flows.

Main Methods:

• Modification of the standard Vicsek model to separate intrinsic and extrinsic noise.
• Simulation of particle dynamics in a Taylor-Green vortex flow at various speeds.
• Quantification of flock morphology, focusing on filamentarity.
• Analysis of particle distribution relative to vorticity and flow patterns.

Main Results:

• A critical flow speed was identified, above which flock filamentarity significantly increases.
• Particles were observed to aggregate in regions of low vorticity, mimicking inertial particle behavior.
• The cooperative motion of particles imparted an effective inertia, influencing flock structure.
• The angle between flow and particle direction followed a power-law distribution.

Conclusions:

• Cooperative particle motion in a flock can lead to effective inertia, altering collective behavior in fluid flows.
• Vortical flows induce particle segregation into low-vorticity zones, enhancing flock filamentarity.
• The modified Vicsek model provides insights into the interplay between self-organization and external fluid dynamics.