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Title:
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Three-dimensional flow structures and vorticity control in fish-like swimming |
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Author:
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Zhu, Q.; Wolfgang, M.J.; Yue, D.K.P.; Triantafyllou, M.S. |
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Abstract:
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We employ a three-dimensional, nonlinear inviscid numerical method, in conjunction
with experimental data from live fish and from a fish-like robotic mechanism, to
establish the three-dimensional features of the flow around a fish-like body swimming
in a straight line, and to identify the principal mechanisms of vorticity control
employed in fish-like swimming. The computations contain no structural model for
the fish and hence no recoil correction. First, we show the near-body flow structure
produced by the travelling-wave undulations of the bodies of a tuna and a giant
danio. As revealed in cross-sectional planes, for tuna the flow contains dominant
features resembling the flow around a two-dimensional oscillating plate over most
of the length of the fish body. For the giant danio, on the other hand, a mixed
longitudinal-transverse structure appears along the hind part of the body. We also
investigate the interaction of the body-generated vortices with the oscillating caudal
fin and with tail-generated vorticity. Two distinct vorticity interaction modes are
identified: the first mode results in high thrust and is generated by constructive
pairing of body-generated vorticity with same-sign tail-generated vorticity, resulting
in the formation of a strong thrust wake; the second corresponds to high propulsive
efficiency and is generated by destructive pairing of body-generated vorticity with
opposite-sign tail-generated vorticity, resulting in the formation of a weak thrust
wake. |
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URI:
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http://hdl.handle.net/1721.1/25620
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Issue Date:
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2002 |
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Publisher:
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Cambridge University Press |
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Keywords:
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flow structures, vorticity control, fish-like |
