Laboratory investigation of air turbulence above simple water waves

Abstract

The structure of turbulent-shear flows above propagating waves is investigated experimentally in a wind and wave facility at the University of Florida. Wave-induced perturbations and their importance in transferring momentum to waves is a central question in this study. The turbulent air velocities were measured in the horizontal and vertical directions by using a two channel hot-film anemometer system. Turbulence measurements were obtained both in the presence and absence of mechanical waves with wave height =8.9 cm and wave speed =2.23 m/sec. Power spectra of air turbulence indicate the presence of significant wave-induced peaks in both the horizontal and vertical velocities at the frequency of mechanical wave. The peaks disappear in the absence of mechanical waves. Calculations of momentum transfer to waves based on the wave-induced Reynolds stress and on the measured growth rate of waves indicate that the interaction of surface waves with the turbulent flow above them produces significant momentum transfer in addition to the wave-induced stress.