Inertial self-propulsion of spherical microswimmers by rotation-translation coupling

Itzhak Fouxon and Yizhar Or
Phys. Rev. Fluids 4, 023101 – Published 5 February 2019

Abstract

We study swimming of small spherical particles that regulate fluid flow on their surface by applying tangential squirming strokes. We derive translational and rotational velocities for any given stroke which is not restricted by axial symmetry as assumed usually. The formulation includes inertia of both the fluid and the swimmer, motivated by inertia's relevance for large Volvox colonies. We show that inertial contribution to mean speed comes from dynamic coupling between translation and rotation, which occurs only for strokes that break axial symmetry. Remarkably, this effect enables overcoming the scallop theorem on impossibility of propulsion by time-reversible strokes. We study examples of tangential strokes of an axisymmetric traveling wave and of asymmetric time-reversible flapping. In the latter case, we find that the inertia-driven mean speed is optimized for flapping frequency and the swimmer's size, which fall well within the range of realistic physical values for Volvox colonies. We conjecture that similarly to Paramecia, large Volvox could use time-reversible strokes for inertia-driven swimming coupled with their rotations.

  • Figure
  • Figure
  • Received 19 November 2017
  • Revised 15 October 2018

DOI:https://doi.org/10.1103/PhysRevFluids.4.023101

©2019 American Physical Society

Physics Subject Headings (PhySH)

Fluid Dynamics

Authors & Affiliations

Itzhak Fouxon1,2,* and Yizhar Or2,†

  • 1Department of Chemical Engineering, Technion–Israel Institute of Technology, Haifa 3200003, Israel
  • 2Faculty of Mechanical Engineering, Technion–Israel Institute of Technology, Haifa 3200003, Israel

  • *itzhak8@gmail.com
  • izi@technion.ac.il

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Issue

Vol. 4, Iss. 2 — February 2019

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