Laboratory Study on the Turbulent Boundary Layers Over Wind-Waves Roughness

Abstract

A laboratory study of turbulent boundary layers over wind-generated waves using Particle Image Velocimetry (PIV) in a wind-wave flume at the University of Melbourne is presented. The experiments are taken at two different wind speeds of 5.5 and 8.5 m/s at a fetch length of 3.5 m. Two types of multi-camera measurement are specifically tailored to capture the flow behaviours. The first is a measurement with high spatial resolution, with aims of characterizing the mean velocity, surface drag and Reynolds stresses over the non-stationary surface. The second type is a large field-of-view measurement, designed to capture the large-scale turbulent motions which are directly associated with the surface-wave topography. Although the turbulent flow is developed over a non-stationary surface (i.e. wind-generated waves), it embodies similarities in both integral parameters and Reynolds stress behaviours to the turbulent flows over stationary rough surfaces. This observation could open a possibility to develop an important turbulence model as well as drag prediction over wind-generated waves, which could be closely related to stationary rough-wall boundary layers.