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Microswimmer-induced chaotic mixing

Published online by Cambridge University Press:  19 August 2015

Mir Abbas Jalali*
Department of Astronomy, University of California, Berkeley, CA 94720, USA Department of Mechanical Engineering, Sharif University of Technology, Azadi Avenue, P.O. Box 11155-9567, Tehran, Iran
Atefeh Khoshnood
Reservoir Engineering Research Institute, Palo Alto, CA 94301, USA
Mohammad-Reza Alam
Department of Mechanical Engineering, University of California, Berkeley, CA 94720, USA
Email address for correspondence:


Efficient mixing, typically characterised by chaotic advection, is hard to achieve in low Reynolds number conditions because of the linear nature of the Stokes equation that governs the motion. Here we show that low Reynolds number swimmers moving in quasi-periodic orbits can result in considerable stretching and folding of fluid elements. We accurately follow packets of tracers within the fluid domain and show that their trajectories become chaotic as the swimmer’s trajectory densely fills its invariant torus. The mixing process is demonstrated in two dimensions using the Quadroar swimmer that autonomously propels and tumbles along quasi-periodic orbits with multi-loop turning trajectories. We demonstrate and discuss that the streamlines of the flow induced by the Quadroar closely resemble the oscillatory flow field of the green alga Chlamydomonas reinhardtii. Our findings can thus be utilized to understand the interactions of microorganisms with their environments, and to design autonomous robotic mixers that can sweep and mix an entire volume of complex geometry containers.

© 2015 Cambridge University Press 

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