A method for visualizing periodic boundary layer phenomena

Abstract

In the course of an experimental investigation of the periodic motion of the transition point on an oscillating wing, it became clear that the method used could be applied also to visualize the periodic boundary layer phenomena on steady aerofoils. The method uses the fact that periodic motions seem to come to rest if they are illuminated by a stroboscopic light source, flashing with the right frequency. By introducing smoke into the boundary layer of a flat plate or an aerofoil and assuming that periodic motions occur, they might be studied easily with stroboscopic illumination.