Impulse generated during unsteady maneuvering of swimming fish |
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Authors: | Brenden P Epps Alexandra H Techet |
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Institution: | (1) Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA |
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Abstract: | The relationship between the maneuvering kinematics of a Giant Danio (Danio aequipinnatus) and the resulting vortical wake is investigated for a rapid, ‘C’-start maneuver using fully time-resolved (500 Hz) particle
image velocimetry (PIV). PIV illuminates the two distinct vortices formed during the turn. The fish body rotation is facilitated
by the initial, or “maneuvering” vortex formation, and the final fish velocity is augmented by the strength of the second,
“propulsive” vortex. Results confirm that the axisymmetric vortex ring model is reasonable to use in calculating the hydrodynamic
impulse acting on the fish. The total linear momentum change of the fish from its initial swimming trajectory to its final
swimming trajectory is balanced by the vector sum of the impulses of both vortex rings. The timing of vortex formation is
uniquely synchronized with the fish motion, and the choreography of the maneuver is addressed in the context of the resulting
hydrodynamic forces. |
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Keywords: | |
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