THEORETICAL SKIN DRAG IS MINOR COMPARED TO FORM DRAG

Novais, L., Marinho, D. A., Reis, V. M., Marquest, M. C., Costa, A. M., Sousa, L. S., Alves, F. B., Vilas-Boas, J. ., Machado, L., Rouboa, A. I., & Silva, A. J. (2009). Contribution of form drag and skin friction drag during swimming gliding. ** ACSM 56th Annual Meeting, Seattle, Washington.** Presentation number 2558.

This study analyzed the relative contribution of the skin friction drag and the form drag for the total drag during gliding. A 3-D domain was created to simulate the fluid flow around a swimmer model. The numerical simulation analysis consisted of the use of a three-dimensional mesh of cells that simulated the flow around the human body. Computational fluid dynamics methodology used the finite volume approach, where the equations were integrated over each control volume. The k-epsilon turbulent model was applied to the flow around a three-dimensional model of a male adult swimmer in two gliding positions: in ventral position with the arms extended at the front and in ventral position with the arms alongside the trunk. The swimmer model middle line was placed at a water depth of 0.90 m, equidistant from the top and bottom surfaces of the 3-D domain. The coefficient of drag was computed using a steady flow velocity of 2 m/s for both gliding situations. The coefficient of drag was decomposed into form and skin friction drag.

The position with the arms extended at the front presented a coefficient of drag value of 0.43 whereas the position with the arms aside the trunk presented a value of 0.74. In the position with the arms extended at the front, form drag and skin friction drag represented, approximately, 87% and 13% of the total drag, respectively. In the position with the arms alongside the trunk, form drag and skin friction drag represented, approximately 92% and 8% of the total drag, respectively.

**Implication**. The gliding position with the arms extended to the front produced lower drag coefficients than with the arms placed alongside the trunk. Although form drag was dominant, skin friction drag was notable during gliding. [These are theoretical values and do not include the important feature of wave drag. The use of a single-subject model does not allow the values reported to be generally attributed to other swimmers.]

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