Effects of wind driven air-water interface waves on turbulent boundary layer structure.

To investigate the interaction between a turbulent boundary layer and unsteady surface topography an experiment was designed in which a turbulent boundary layer was formed along a wind tunnel floor, with a section of the floor replaced with a shallow water pool of variable geometry. In this experiment, the zero-pressure-gradient turbulent boundary layer was allowed to develop over a smooth wall before it reached the water surface. The velocity of air was selected to produce wind-driven surface waves in the pool of semi-regular wavelength and periodicity, with the waves serving to act as roughness perturbing boundary layer flow. The air-water interface geometry was characterized under these conditions, with the dominating wavelength, frequency and phase speed identified. The turbulent boundary layer characteristics were measured with hot-wire anemometry at several wall-normal locations upstream of the water pool, at multiple streamwise locations above, and at locations downstream the pool. These measurements allowed the turbulent boundary layer was characterized, including the formation and development of the internal layer, and effects of waves perturbation were studied by comparison to boundary layer formed over a smooth wall under the same conditions.