431046 A Squirmer Across Reynolds Numbers

Wednesday, November 11, 2015: 9:30 AM
150A/B (Salt Palace Convention Center)
Nicholas G. Chisholm1, Dominique Legendre2, Eric Lauga3 and Aditya S. Khair1, (1)Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA, (2)Interface, Institut de Mécanique des Fluides de Toulouse, Toulouse, France, (3)Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, United Kingdom

The self-propulsion of a spherical squirmer – a model swimming organism that achieves locomotion via steady tangential movement of its surface – is quantified across small to large Reynolds numbers (Re) via numerical solution of the Navier-Stokes equations.  A fixed swimming stroke is considered.  We show that fluid inertia leads to profound differences in the locomotion of so-called pusher versus puller squirmers.  The swimming speed of a pusher increases monotonically with increasing Re.  In contrast, a puller first slows down with increasing Re and then speeds up. We show that the large Re flow around a pusher is essentially irrotational (akin to a spherical bubble), while a large vortical structure develops at the rear of a puller (akin to a no-slip sphere under an external force). Consequently, it is found that the steady axisymmetric locomotion of a pusher is stable to Re that far exceed that of a puller or even a no-slip sphere.  Additionally, we quantify fluid mixing at finite Re by a dilute collection of squirmers via the mechanism of drift diffusion. Here, we show that pullers, while less efficient swimmers, achieve a greater degree of mixing than pushers.

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See more of this Session: Bio-Fluid Dynamics
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