Author(s): Michio Sanjou; Iehisa Nezu; Akihiro Toda
Linked Author(s): Michio Sanjou
Keywords: Coherent structure; Wind-induced water waves; PIV measurements; Phase analysis
Abstract: When wind appears over the free surface, water waves and turbulence are generated by an interfacial shear stress. In particular, turbulent diffusion promotes mass and momentum transport beneath the interface between air and water significantly in ocean and lakes, and thus it is very important for global environment problems to reveal such turbulence property and coherent structure. Some previous studies pointed out that the turbulence generation depended on the phase of water waves, in which single-point measurements by a laser Doppler anemometer (LDA) were conducted intensively. However, there remain uncertainties about the effects of wave phases on coherent turbulence motion, e.g., sweeps&ejections, and streak structure. Simultaneous measurements of velocities and free-surface elevation allow us to conduct reasonably the phase analysis of the coherent structure in interfacial shear layer. Furthermore, multi-point measurements such as PIV are very powerful to detect the spacetime structure of coherent motions. Therefore, in the present study, we developed a specially designed PIV system that can measure the velocity components and surface-elevation fluctuations simultaneously by using two sets of high-speed cameras to reveal the coherent structure in interfacial shear layer.
Year: 2010