Essay About Downward Kick And Injection Of Air Bubbles

Vortices And Propulsion
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VORTICES AND PROPULSION
RaДєl Arellano
Universidad de Granada (Spain)
A review of the general theory of swimming propulsion is presented relating this
with knowledge about vortices in steady and unsteady flow conditions. Three
methods of flow visualisation have been used in the experiments: a) injecting air
bubbles close to big toe during undulatory underwater swimming and breaststroke
kick; b) putting reflective particles in water to see hand short movements and; c)
injection of air bubbles in the swimming pool creating a “bubble wall”, making it
possible for the swimmer to cross and to swim along it. The results of the
experiments showed that: a) vortices are generated during different phases of the
stroke and during the downward kick in undulatory swimming, flutter kick and
breaststroke kick; b) when the hand suddenly changes the direction of its
movement the starting vortex is detached from the hand and; c) the size and
movement characteristics of the vortex seem related to propulsion obtained by the
hand and foot movements.
KEY WORDS: swimming propulsion, vortex, flow visualisation, bubble wall.
INTRODUCTION: THE BASICS OF SWIMMING PROPULSION: The total mechanical
power (Po) produced by the swimmer (assuming a constant velocity) equals the power to
overcome active drag (Pd) plus power expended in giving masses of water pushed away a
kinetic energy change (Pk) (Toussaint, 1992):
Po = Pd + Pk (1)
(Counsilman, 1971) stated that efficient propulsion is obtained by pushing a large mass of
water a short distance without much acceleration. Greater efficiency in water is achieved by
moving a large amount of water a short distance than by moving small amounts of water a
great distance. These statement were developed after observing how good swimmers pull
in the water with complex 3D trajectories that show continuous changes of the direction of
the hands pulling path. Later (Martin, 1989) speaking about the fundamental principles in
swimming asserted that swimming by propelling water, one may achieve a given amount of
thrust either by accelerating a large mass of water to a small velocity