Abstract
A non-harmful system to visualize the flow around an entire swimmer in a regular swimming pool is developed. Small air bubble tracers are injected through the bottom of the swimming pool in a prescribed measurement area. The motion of these bubbles, which will be largely induced by the swimmer’s motion, is captured by a camera array. The two-dimensional velocity field of the water at arbitrary planes of interest can be resolved using a refocussing method in combination with an optical visualisation method, based on particle image velocimetry, which is commonly used in fluid dynamics research. Using this technique, it is possible to visualize coherent flow structures produced during swimming; it is demonstrated here for the dolphin kick.
Highlights
New insights in propulsion mechanisms and resistance can be gained by studying the swimmer from a hydrodynamical point of view
The vortices produced during the kicks could be visualized using particle image velocimetry (PIV)
It is peculiar that in most cases only the vortices after the down kick could be made visible. It seems that the vortices produced after the up-kick are weaker, smaller or less coherent, and are not captured by the PIV analysis
Summary
New insights in propulsion mechanisms and resistance can be gained by studying the swimmer from a hydrodynamical point of view. Studying the flow structures emerging in this wake can give insight into the forces both experienced and applied by the swimmer, and may be used as a diagnostic for the efficiency of the swimming technique. The strength, size and direction of motion of coherent vortex structures and the interaction of the swimmer with these structures are all expected to be related to the swimming efficiency. This article is a part of Topical Collection in Sports Engineering on Measuring Behavior in Sport and Exercise, edited by Dr Tom Allen, Dr Robyn Grant, Dr Stefan Mohr and Dr Jonathan Shepherd.
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