Swimming in Potential Flow

Author: Glisman, Alec Gregory

Year: 2022

Degree: Master's thesis

Advisor: Brady, John F.

Committee Members: Wang, Zhen-Gang; Colonius, Tim; Hunt, Melany L.; Brady, John F.

Option: Chemical Engineering

DOI: 10.7907/6xkb-rs66

Abstract

Active bodies undergo self-propulsive motion in a fluid medium and span a broad range of length and time scales. This report focuses specifically on the motion at high Reynolds number, where inertial forces dominate the fluid dynamics. Many active systems spontaneously self-organize into visually striking structures: fish schooling, birds flocking, and bacterial colonies growing. Current models of emergent behavior in the inertial regime are mainly phenomenological and do not account for the fluid-mediated interactions between bodies. We seek to advance physical models of swimmers in high inertia environments. To this end, we explicitly model the hydrodynamics to discern what role the fluid medium plays in active group dynamics and whether it can reproduce the observed emergent phenomenon without the imposition of phenomenologically based interaction rules.

A minimal swimmer model consisting of three linked spheres is constructed, and we find self-propulsion without external forces or momentum transfer via vortex shedding. The inertial swimmer is also compared to an identical swimmer in the Stokes regime---where fluid inertia is neglected. The Stokes hydrodynamics are longer-ranged at leading order, and we demonstrate that the stronger hydrodynamic interactions lead to a greater center of mass translation after a period of articulation.

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