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Fluid transport by individual microswimmers

Published online by Cambridge University Press:  30 May 2013

Dmitri O. Pushkin*
Affiliation:
Rudolf Peierls Centre for Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, UK
Henry Shum
Affiliation:
Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA
Julia M. Yeomans
Affiliation:
Rudolf Peierls Centre for Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, UK
*
Email address for correspondence: mitya.pushkin@gmail.com

Abstract

We discuss the path of a tracer particle as a microswimmer moves past on an infinite, straight trajectory. If the tracer is sufficiently far from the path of the swimmer it moves in a closed loop. As the initial distance between the tracer and the path of the swimmer $\rho $ decreases, the tracer is displaced a small distance backwards (relative to the direction of the swimmer velocity). For much smaller tracer–swimmer separations, however, the tracer displacement becomes positive and diverges as $\rho \rightarrow 0$. To quantify this behaviour we calculate the Darwin drift, the total volume swept out by a material sheet of tracers, initially perpendicular to the swimmer path, during the swimmer motion. We find that the drift can be written as the sum of a universal term which depends on the quadrupolar flow field of the swimmer, together with a non-universal contribution given by the sum of the volumes of the swimmer and its wake. The formula is compared to exact results for the squirmer model and to numerical calculations for a more realistic model swimmer.

Type
Papers
Copyright
©2013 Cambridge University Press 

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