Characteristics of the Wind-induced Waves and Air-water Interaction Process

In this study, a wind tunnel tank (25.5m in length) was used to investigate the coupling relationship between wind and wind-induced waves. Simultaneous MCAS (Multi-Channel Anemometer System) and DPIV (digital particle image velocimetry) were employed to systematically investigate statistical characteristics of wind-induced waves, near-surface airflow structures (mean and instantaneous), interface friction between air-water interface and hydrodynamic characteristics of wave at six spaced sections with wind speeds ranging from 3 to 15m s⁻¹. The wind-induced waves present a typical changing trend with fetch and wind speed, as soon as their vertical-wise asymmetric. The phase velocities of the waves were computed directly using image matching technique, and relations between phase velocity and waveform parameters were build and compared with the results of several theories and experiments. The air flow boundary layer over the water waves shows a logarithmic mean velocity profile for all the experimental cases. Comparison of air-water boundary layer and air-plain boundary layer shows that the thickness of the boundary layer over the water waves grows much faster than the boundary layer over a plain stalinite wall and the apparent roughness is related to the wave amplitude. Friction coefficient of air-water interface was calculated based on horizontal mean wind velocity profiles and is compared with the results of previous experiments. Furthermore, characteristics of velocity distribution and rate of dissipation of turbulent kinetic energy along wave crest-cross vertical line and trough-cross vertical line were investigated based on PIV data, and results showed that the mean velocity profiles of water side is also logarithmic, and the rate of dissipation of turbulent kinetic energy of crest-cross vertical line and trough-cross vertical line is associated with wave breaking near wave surface.