Experiments of swimming motion of a biomimetic flexible caudal fin under the influence of K?rm?n vortex street
Date Issued
2016
Date
2016
Author(s)
Yang, Wen-Chi
Abstract
In nature, the function behind the schooling behavior of fishes mainly is to defend themselves from large predators, and to use kinetic energy generated by the external environment to achieve a better swimming efficiency. For an individual among the schooling fish, the wake flow generated from the fishes that are ahead and upstream is affected by the Karman vortex. As a result, this experiment uses the Karman vortex flow field generated by a semicircular cylinder, and places a flexible fish model downstream, to observe the effect of the Karman vortex on the force and swing condition of the fish model. Predecessors of this research principally used computer simulation to conduct the experiment. They used slightly lower Reynolds number of the flow field, and had more free oscillation of the fish’s tails. Semicircular cylinders were used to generate the Karman vortex, and live fishes were placed within the flow field. The results provided by filming the fish''s tail swing frequency, size of the fish and the ideal resting location of the fish provided the predecessors of the experiment with their statistical calculations. We placed similar fish models in the flow field for force measurement and increase the Reynolds number of the operation. The experimental result differs from the citations in that the usage of live fish models failed to measure force and failed to calculate the slightly lower Reynolds number of flow fields detected by computer simulation. Within the resulting Reynolds number of 14400, 19200, 24000; it is found that 1.5D downstreams from the Karman vortex producing fish model, additional thrust and a maximal Strouhal number provided by the external flow field is detected. Therefore, we conclude that the ideal location for fishes to navigate is at 1.5D downstreams from the Karman vortex.
Subjects
Karman vortex street
semicylinder
cylinder
flexible caudal fin
Type
thesis
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