PRESSURE DISTRIBUTION OVER A MOVING WAVY BOUNDARY

Abstract

Experimental data on pressure distribution over a sinu^ soidal wavy boundary with a fixed and a moving condition, mea_ sured in a water tunnel, are presented for a number of flow - velocities. The model with the moving boundary condition is related to the situation prevailing in the steady state flow picture of a small amplitude wind-generated gravity wave in - which the water flow represents the air flow in nature, while the "fixed in space" moving wavy boundary corresponds to the nearly constant water particle velocity at the surface of the wave. The results show that the normal stress distribution - over a moving boundary differs from that over a fixed one by a phase-lag with respect to the wave shape, which varies with the ratio of flow velocity to the boundary velocity (wave celerity), as predicted by the recent theories of Miles and Ben_ jamin. These results provide an explanation for the energy - transfer from wind to wave due to normal stresses and show that those experiments performed on fixed boundary models can not be associated with the phenomena of water wave generation.