An experimental study on turbulent coherent structures near a sheared air-water interface
Shuangfeng Wang Fu Jia Zhennan Niu Zhangzhi Wu
Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China State Key Laboratory for Turbulence Research, Peking University, Beijing 100871, China State Key Laboratory for Turbulence Research, Peking University, Beijing 100871, China
Abstract The turbulence structures near a sheared air-water interface were
experimentally investigated with the hydrogen bubble visualization technique. Sur-
face shear was imposed by an airflow over the water flow which was kept free from
surface waves. Results show that the wind shear has the main influence on coher-
ent structures under air-water interfaces. Low- and high- speed streaks form in the
region close to the interface as a result of the imposed shear stress. When a certain
airflow velocity is reached, "turbulent spots" appear randomly at low-speed streaks
with some characteristics of hairpin vortices. At even higher shear rates, the flow
near the interface is dominated primarily by intermittent bursting events. The coher-
ent structures observed near sheared air-water interfaces show qualitative similarities
with those occurring in near-wall turbulence. However, a few distinctive phenomena
were also observed, including the fluctuating thickness of the instantaneous boundary
layer and vertical vortices in bursting processes, which appear to be associated with
the characteristics of air-water interfaces.
Shuangfeng Wang,Fu Jia,Zhennan Niu et al. An experimental study on turbulent coherent structures near a sheared air-water interface[J]. Acta Mechanica Sinica, 1999, 15(4): 289-298.
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