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

Abstract

We derive from first principles a three-dimensional theory of self-propelled particle swarming in a viscous fluid environment. Our model predicts emergent collective behavior that depends critically on fluid opacity, mechanism of self-propulsion, and type of particle-particle interaction. In "clear fluids" swimmers have full knowledge of their surroundings and can adjust their velocities with respect to the lab frame, while in "opaque fluids," they control their velocities only in relation to the local fluid flow. We also show that "social" interactions that affect only a particle's propensity to swim towards or away from neighbors induces a flow field that is qualitatively different from the long-ranged flow fields generated by direct "physical" interactions. The latter can be short-ranged but lead to much longer-ranged fluid-mediated hydrodynamic forces, effectively amplifying the range over which particles interact. These different fluid flows conspire to profoundly affect swarm morphology, kinetically stabilizing or destabilizing swarm configurations that would arise in the absence of fluid. Depending upon the overall interaction potential, the mechanism of swimming (e.g., pushers or pullers), and the degree of fluid opaqueness, we discover a number of new collective three-dimensional patterns including flocks with prolate or oblate shapes, recirculating peloton-like structures, and jet-like fluid flows that entrain particles mediating their escape from the center of mill-like structures. Our results reveal how the interplay among general physical elements influence fluid-mediated interactions and the self-organization, mobility, and stability of new three-dimensional swarms and suggest how they might be used to kinetically control their collective behavior.

References in corpus (13)

• Novel type of phase transition in a system of self-driven particles
• The hydrodynamics of swimming microorganisms
• Hydrodynamics of self-propulsion near a boundary: predictions and accuracy of far-field approximations
• Propulsion in a viscoelastic fluid
• State Transitions and the Continuum Limit for a 2D Interacting, Self-Propelled Particle System
• Hydrodynamics of self-propelled hard rods
• Swimming speeds of filaments in nonlinearly viscoelastic fluids
• Theory of swimming filaments in viscoelastic media
• A model for rolling swarms of locusts
• Pattern formation in flocking models: A hydrodynamic description
• Flapping motion and force generation in a viscoelastic fluid
• Generalized fundamental solutions for unsteady viscous flows
• Life at high Deborah number

Cited by in corpus (5)

• Analyzing Collective Motion with Machine Learning and Topology
• Synchronized oscillations in swarms of nematode Turbatrix aceti
• Collective behavior of self-steering active particles with velocity alignment and visual perception
• Emergence of a giant rotating cluster of fish in three dimensions by local interactions
• Effect of gravitational field on collective motion of fish