Turbulent Flow Over Moving Boundary

To gain a better understanding of the mechanism of energy transfer from wind to an already formed small amplitude gravity water wave, pressure and velocity measurements were performed in a model in which the wave surface was reproduced by a wavy boundary moving at constant speed. Experiments were carried out in a water flume with two different sets of sinusoidal shape wavy boundaries under fixed and moving conditions. It was found that, while the pressure distribution was almost symmetrical when the boundary was fixed, it displayed a noticable phase-lag with respect to the waves shape when the boundary was moving, which accounts for the energy transfer from wind to wave because of the normal stress. Within the limitations of experimental accuracy the data coincides with the curves computed for each case from Miles' mathematical theory. In addition, flow visualization experiments provided a qualitative verification of the existance of a stationary vortex over the wave, as predicted by Lighthill in his physical explanation of the phenomena.