Relationship between Dynamic Lift and Streamwise Vortices Acting on a Disk Simulating a Hand of Swimmer

概要

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The issue of whether propulsion in swimming is due primarily to lift or drag appeared to have been settled in the early 1970s. Prior to that time it was believed that the best way to propel the body forward was to pull the hand directly backwards to use drag forces. In addition, the actual motion of a hand in swimming is obviously unsteady and the time-dependent fluid forces called the "dynamic lift" have to be taken into account. In this study, unsteady fluid forces acting on a disc simulating a human hand and the vortical flow field were investigated in the (sinusoidal) pitching motion. The wind tunnel test using the three-dimensional model is effective for understanding the relationship between the dynamic lift and the fundamental structure of the vortex system. It is confirmed that the pitching motion is available for keeping lift higher after the separation occurs. The delay of stall is observed and also a much larger lift force than the quasi-steady-state value is obtained in the pitching motion. The dynamic lift acting on a pitching disk is strongly influenced by vortices shed from the outer edge of the disk. The lift force becomes larger as the vortices develop and the dynamic stall occurs at the instance of collapse in shape of the vortices.
社団法人日本流体力学会の論文