Swarming in viscous fluids: Three-dimensional patterns in swimmer- and force-induced flows

Area of Science:

• Physics
• Fluid Dynamics
• Soft Matter Physics

Background:

• Self-propelled particle systems exhibit complex collective behaviors.
• Fluid environments significantly influence particle interactions and emergent dynamics.
• Understanding 3D swarm formation requires considering fluid-mediated forces.

Purpose of the Study:

• To develop a 3D theory for self-propelled particle swarming in viscous fluids.
• To investigate the impact of fluid opacity and particle interactions on swarm behavior.
• To identify emergent collective behaviors and novel 3D swarm patterns.

Main Methods:

• Derivation of a three-dimensional theoretical model for particle swarming.
• Analysis of particle behavior in both clear and opaque fluid environments.
• Distinction between social and physical particle-particle interactions and their fluid-mediated effects.

Main Results:

• Collective behavior critically depends on fluid opacity, propulsion mechanism, and interaction type.
• Social interactions induce different flow fields than direct physical interactions.
• Discovered new 3D swarm patterns: prolate/oblate flocks, peloton-like structures, and jet flows.

Conclusions:

• Fluid-mediated interactions profoundly affect swarm morphology, stability, and mobility.
• Interplay of physical elements dictates self-organization and emergent 3D swarm behavior.
• Results suggest methods for kinetically controlling collective swarm dynamics.