The effect of depth on drag during the gliding phase in swimming
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The gliding phase following a swimming start or turn is an
important component of the overall swimming performance.
PURPOSE: To analyse the effect of depth on hydrodynamic drag
force during the underwater gliding, using computational fluid
dynamics.
METHODS: A three-dimensional domain was created to simulate the fluid flow around a swimmer model, representing the
geometry of part of a lane in a swimming pool. The water depth
of this domain was 1.50 m with a 3.0 m width and 11.0 m length.
Computational fluid dynamics methodology was used to perform
numerical simulations in the created domain which was divided
into a number of mesh cells. The k-epsilon turbulent model was
applied to the flow around a three-dimensional model of a male
adult swimmer in a prone gliding position with the arms
extended at the front. General moving object model was used to
simulating the body as the displacing object. During the gliding,
the swimmer model’s middle line was placed at three different
water depths: at 0.20 m (just under the surface), at 0.75 m
(middle of the pool), and at 1.30 m (bottom of the pool). The
drag coefficient and the hydrodynamic drag force were
computed using a steady velocity of 2.50 m/s for the different
depths run for 3 s in each case.
RESULTS: The drag coefficient was 0.37, 0.34 and 0.30 and the
drag force was 141.40 N, 128.10 N and 115.30 N when gliding at
a water depth of 0.20 m, 0.75 m and 1.30 m, respectively, at the
time of 2 s when the swimmer was approximately at the middle
of the computational pool.
CONCLUSIONS: The hydrodynamic drag values for the gliding
decreased with the increase in depth. This decrease of drag
values with depth can be due to the reduction of the wave drag
effect, which has an important contribution to total drag near
the water surface. Reducing the drag experienced by swimmers
during the glide off the wall can decrease start and turn times
and unnecessary energy loss. Hence, these results suggested
that gliding at 0.75 m under the water surface or deeper seemed
to be an optimal gliding depth for minimizing drag and improve
swimming performance
