Experimental measurements of the turbulence characteristics under sheared air-water interfaces

Measurements of mean velocity and turbulent quantities are carried out under sheared air-water interfaces. Surface shear was imposed by an airflow over the water flow which was kept free from surface waves. Results indicate that, when the shearing airflow is relatively strong (interface friction velocity on water side μ_τ ≥ 0.20 cm/s), distributions of mean velocity, turbulence intensities and Reynolds shear stress near the water surface are similar to those observed in near-wall turbulence, suggesting the similarity of turbulent coherent structures in the two flows. On the other hand, the present data also show some characteristics peculiar to sheared air-water interfaces. In the flow field close to sheared air-water interfaces, velocity fluctuations both in streamwise and in vertical directions are damped. This is a notable feature that distinguishes turbulence near sheared air-water interface and free-surface turbulence.