Generation of surface waves by turbulent wind flow

The turbulent wind flow passing over small-amplitude moving surface waves is studied analytically by means of first-order closure models. The air flow is set to flow past a two-dimensional moving water surface of mild wave slopes. Following the asymptotic structure developed by and Belcher et al. (1993). the entire flow field is divided into a three-layer structure. Using this flow division, the flow based on the stream function and the wave-growth rate are obtained through asymptotic expansions. It is found that the wind flows along the streamline of the water surface in the inner region. As the wind ascends along the wave, the wind accelerates until it reaches the wave crest. This upward lift produces the necessary shear for energy transfer to the surface waves and wave starts to grow asymmetrically along the wavelength. On the downwind side, the flow decelerates and this produces an additional surface shear stress. The resultant summative effect produces a flow characteristics typical of that past an undulating rough surface. It is also found that the growth rate of the waves depends on the turbulence model. Our model is compared with other laboratory and field measurements and reasonable agreement is obtained.