Effect of 3-Dimensional Airfoil Shape in Pitching Motion on Unsteady Fluid Forces

Abstract

In the present study, in order to investigate unsteady effects on propulsion during front crawl swimming, unsteady fluid forces acting on a discoid airfoil simulating a human hand and the vortical flow field were measured in the (sinusoidal) pitching motion for the wind tunnel test, because the motion of a hand in swimming is obviously unsteady. The wind tunnel test has the advantage to enable many unsteady parameters to be changed easily. The pitching motion is available for keeping lift higher after the separation occurs. The delay of stall was observed and also a much larger lift force than the quasi-steady-state value was obtained in the pitching motion. In addition, the hysteresis in dynamic lift curve during the pitching motion decreased with increasing the pitching frequency. The unsteady effects of the pitching airfoil were affected by the stall characteristics of an airfoil under the stationary conditions.