INVESTIGATION OF THE VELOCITY FIELD OVER WAVES USING A WAVE FOLLOWER

Abstract : The turbulent velocity field over simple propagating waves is investigated by hot-film sensors in a wind and wave facility. Use is made of a wave follower to obtain measurements below the wave crest level. Turbulence measurements are obtained in a wave following frame over the range 1.75 - 25 cm above the instantaneous water level. The measurements are transformed to an Eulerian frame and compared to measurements obtained from fixed probes over a height range 10-50 cm above the mean water level. In the overlap region the transformed wave following results are in reasonable agreement with the fixed probes results. The measurements below the crest level indicate rapid variations in Reynolds stresses and wave induced velocities. The results suggest nonlinear wave induced perturbations close to the water surface and reveal weaknesses in assumptions adopted in recent theoretical models of turbulent shear flows over waves. (Author)