Near-surface flow structure over wind-generated water waves, part II: characteristics of separated and non-separated flows

Abstract

This article is the continuation of the previous work reported in the companion paper (part I). The same experimental data were further investigated to compare the airside flow behavior over separated and non-separated flow fields over wind-generated water waves. Particle image velocimetry technique was used to measure the two-dimensional velocity fields at wind speeds of 3.7 and 4.4 m s−1 and at a fetch of 2.1 m. An algorithm was developed to segregate separated and non-separated velocity fields within the measured dataset. The results show that the waves over which the flow separation occurs are steeper and larger in amplitude than the waves with no flow separation. The results also show that the influence of flow separation is mainly restricted on the crest-to-trough region. Within the separation region, lower magnitudes of the streamwise velocity and higher magnitudes of the vorticity were observed for the separated flow than that for the non-separated flow fields. The turbulence is significantly enhanced within the separation zone. It was also observed that the flow separation did not influence the turbulence behavior and magnitude on the windward side of the wave. The enhanced Reynolds stress is positive on the leeward side which indicates that the flow separation increases downward momentum transfer from wind to the wave. The profiles of the wave-induced velocity and Reynolds stress show that the flow separation influences the wave-induced characteristics over the entire waveform.