The aim of this study was to analyze the effects of depth on drag during the streamlined glide in swimming using Computational Fluid Dynamics. The Computation Fluid Dynamic analysis consisted of using a three-dimensional mesh of cells that simulates the flow around the considered domain. We used the K-epsilon turbulent model implemented in the commercial code Fluent® and applied it to the flow around a three-dimensional model of an Olympic swimmer. The swimmer was modeled as if he were gliding underwater in a streamlined prone position, with hands overlapping, head between the extended arms, feet together and plantar flexed. Steady-state computational fluid dynamics analyses were performed using the Fluent® code and the drag coefficient and the drag force was calculated for velocities ranging from 1.5 to 2.5 m/s, in increments of 0.50m/s, which represents the velocity range used by club to elite level swimmers during the push-off and glide following a turn. The swimmer model middle line was placed at different water depths between 0 and 1.0 m underwater, in 0.25m increments. Hydrodynamic drag decreased with depth, although after 0.75m values remained almost constant. Water depth seems to have a positive effect on reducing hydrodynamic drag during the gliding. Although increasing depth position could contribute to decrease hydrodynamic drag, this reduction seems to be lower with depth, especially after 0.75 m depth, thus suggesting that possibly performing the underwater gliding more than 0.75 m depth could not be to the benefit of the swimmer.
Background The swimmer's body position after immersion determines the success of the start rather than his/her starting body position in the block or during the fly. 1 There are swimmers gliding in a lateral position whereas others prefer a prone one. Moreover, during this phase, swimmers may alter their body posture and, as far as some techniques are concerned, swimmers must change the position of the limbs. 2 The purpose of this study was to analyze the effects of body positions in drag coefficient during the glide in swimming using computational fluid dynamics. Methods In order to create the three-dimensional digital model computer tomography scans of a human body of a male swimmer were applied 3 . The swimmer was modelled as if he were gliding underwater in a streamlined position, at four different body positions: (i) in the prone position, (ii) in a side position with an absolute angle between the horizontal plane with the body coronal plane of 45°, (iii) in a side position with 90°of rotation and, (iv) in the dorsal position. The boundary conditions of the model were designed to represent the geometry and flow conditions of a part of a lane in a swimming pool. Steady-state computational fluid dynamics analyses were performed using the Fluent® code and the drag coefficient was computed for velocities of 1.5, 2.0 and 2.5 m/s. Results Drag coefficient reaches its lowest value in the prone position, followed by the side position with 45°of rotation (0.29%, 0.15%, 0.01% drag increment for 1.5, 2.0, and 2.5 m/s, respectively), the side position with 90°of rotation (1.03%, 0.94%, 0.64% increment), and the dorsal position (2.21%, 1.42%, 0.96% increment), in which the highest value of drag coefficient is obtained. Discussion/ConclusionsMain data shows that the prone position presented the lowest drag coefficient values, whereas dorsal position presented the highest values during the underwater 32 of 39 Br J Sports Med 2013;47:e3Abstracts gliding. The prone position seems to be the one that should be adopted after the starts and turns phases of a competitive swimming event, especially during freestyle events and after pushing-off from the wall during the turn where swimmers can freely choose the best body position.
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