Microswimmers in an axisymmetric vortex flow

Abstract

Microswimmers are encountered in a wide variety of biophysical settings. When interacting with flow fields, they show interesting dynamical features such as trapping, clustering, and preferential orientation. One important step towards the understanding of such features is to clarify the interplay of hydrodynamic flows with microswimmer motility and shape. Here, we study the dynamics of ellipsoidal microswimmers in a two-dimensional axisymmetric vortex flow. Despite this simple setting, we find surprisingly rich dynamics, which can be comprehensively characterized in the framework of dynamical systems theory. By classifying the fixed-point structure of the underlying phase space as a function of motility and microswimmer shape, we uncover the topology of the phase space and determine the conditions under which microswimmers are trapped in the vortex. For spherical microswimmers, we identify Hamiltonian dynamics, which are broken for microswimmers of a different shape. We find that prolate ellipsoidal microswimmers tend to align parallel to the velocity field, while oblate microswimmers tend to remain perpendicular to it. Additionally, we find that rotational noise allows microswimmers to escape the vortex with an enhanced escape rate close to the system's saddle point. Our results clarify the role of shape and motility on the occurrence of preferential concentration and clustering and provide a starting point to understand the dynamics in more complex flows.

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Cited by in corpus (10)

• Jeffery's orbits and microswimmers in flows: A theoretical review
• Transport barriers to self-propelled particles in fluid flows
• Trapping of swimmers in a vortex lattice
• Reaching for the surface: Spheroidal microswimmers in surface gravity waves
• Active Particle Diffusion in Convection Roll Arrays
• Microswimmer trapping in surface waves with shear
• Alignment of elongated swimmers in a laminar and turbulent Kolmogorov flow
• Noise-induced aggregation of swimmers in the Kolmogorov flow
• Trapping microswimmers in acoustic streaming flow
• Active Caustics