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Optimal morphokinematics for undulatory swimmers at intermediate Reynolds numbers

Published online by Cambridge University Press:  19 June 2015

Wim M. van Rees
Affiliation:
Chair of Computational Science, ETH Zurich, Clausiusstrasse 33, 8092 Zurich, Switzerland
Mattia Gazzola
Affiliation:
School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138, USA
Petros Koumoutsakos*
Affiliation:
Chair of Computational Science, ETH Zurich, Clausiusstrasse 33, 8092 Zurich, Switzerland
*
Email address for correspondence: petros@ethz.ch

Abstract

Undulatory locomotion is an archetypal mode of propulsion for natural swimmers across scales. Undulatory swimmers convert transverse body oscillations into forward velocity by a complex interplay between their flexural movements, morphological features and the fluid environment. Natural evolution has produced a wide range of morphokinematic examples of undulatory swimmers that often serve as inspiration for engineering devices. It is, however, unknown to what extent natural swimmers are optimized for hydrodynamic performance. In this work, we reverse-engineer the morphology and gait for fast and efficient swimmers by coupling an evolution strategy to three-dimensional direct numerical simulations of flows at intermediate Reynolds numbers. The fastest swimmer is slender with a narrow tail fin and performs a sequence of C-starts to maximize its average velocity. The most efficient swimmer combines moderate transverse movements with a voluminous head, tapering into a streamlined profile via a pronounced inflection point. These optimal solutions outperform anguilliform swimming zebrafish in both efficiency and speed. We investigate the transition between morphokinematic solutions in the speed–energy space, laying the foundations for the design of high-performance artificial swimming devices.

Type
Papers
Copyright
© 2015 Cambridge University Press 

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Footnotes

Present address: School of Engineering and Applied Sciences, Harvard University, USA.

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