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In the early 1970s, the issue of whether propulsion in swimming is due primarily to lift or drag appeared. 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. Furthermore, the actual motion of a hand in swimming is obviously unsteady and the time-dependent fluid forces have to be taken into account. In this study, unsteady fluid forces acting on a disc simulating a human hand were measured in the (sinusoidal) pitching motion. It is confirmed that the pitching motion is available for keeping lift higher after the separation occurs. The delay of stall for the pitching disk is observed and also the value of maximum lift coefficient is greater than the maximum lift coefficient under stationary condition. In addition, the experiments were carried out in the anharmonic periodic pitching motion which has the different pitching rate between the up-stroke and the down-stroke during one cycle. The peaks of the lift and drag curves in the anharmonic pitching motion are shifted against time compared to those in the sinusoidal pitching motion.

Unsteady Fluid Forces Acting on a Disk Simulating a Hand of Swimmer