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1 Acta of Bioengineering and Biomechanics

1 2005

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Experimental assessment of the drag coefficient during butterfly swimming in hydraulic flume

Taiar R., Bertucci W., Letellier Th., Benkemis I., Toshev Y.

Acta of Bioengineering and Biomechanics

2005

Vol. 7, nr 2

98-108

A body when moving in a fluid is to withstand drag that is proportional to the drag coefficient, the frontal surface area, and the square of the body velocity relative to the fluid velocity (VOGEL [14]). The aim of our study was to determine the relationships between the drag coefficient (CD) and the Reynolds number (Re) for a high-level swimmer. In TAIAR et al. [12], three most propulsive butterfly positions have been defined: the end of the external sweep (beginning of the cycle), the end of the internal sweep (middle of the cycle), and the end of the thrust (end of the cycle). These three positions were reproduced using real-size mannequins articulated ui real-velocity conditions. Experiments have been done ui the large-scale hydraulic flume of the University' of Nantes. Two types of the curves CD (Re) were obtained: for the "best swimmer" and for ''other swimmers". Following the swimming of the ex-word champion Pankratov during the World Championship m Rome (1994) the mannequin representing the "best swimmer" has been positioned similarly to the ex-world champion at the beginning, in the middle and at the end of cycle. The body positions of Pankratov have been obtained using the image analysis software Schleihaui 4.0. In order to obtain the curves CD (Re) representing "other swimmers", the body positions of lower-level swimmers have been used at the beginning, in the middle and at the end of swimming cycle. The two types of curves show well the gap between the techniques of the "best swimmer" and "other swimmers". Our study shows the importance of the body position dining the swimming cycle to minimizing the drug and to assuring better propulsion, i.e. better performance. The results show that the most effective swimmers optimise the body positions in order to reduce the frontal surface and therefore to minimize the drag.