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Visualization of Mechanical Processes: An International Online Journal
ADVECTION FEATURES OF WATER SURFACE PROFILE IN TURBULENT OPEN-CHANNEL FLOW WITH HEMISPHERE ROUGHNESS ELEMENTS
Visualization Research Center, Niigata University, 8050 Ikarashi-2, Nishi, Niigata, Japan, 950-2181
Department of Civil Engineering, Graduate School of Engineering Kobe University, 1-1 Rokkodai-cho, Nada, Kobe, 657-8501, Japan
An open-channel water surface exhibits various types of surface features with the increase of flow rate. In the actual river flow conditions, such features can be utilized as a kind of surface flow indicator or a natural tracer since they are considered to be advected with the surface flow once generated at the water surface. However, such a surface flow feature has not been investigated in detail in the laboratory scale, especially in terms of the relationship between the advection speed of surface features and a water surface velocity just beneath the water surface. Therefore we conducted simultaneous measurements of a water surface and a velocity distribution in a longitudinal vertical plane for a rough wall composed of hemisphere roughness particles as a candidate of rough wall turbulence. Internal velocity fields were analyzed by particle tracking velocimetry (PTV) and water surface velocity was measured by surface tracers, while water surface advection speed was measured by analyzing space time evolutions of a water surface profile, which is an interface between air and water. It was experimentally made clear that the surface patterns are advected with a speed almost comparable to the surface flow velocity within the range of hydraulic conditions examined and water surface configuration is closely related to upwelling large-scale vortices impinging on the water surface.
KEY WORDS: rough wall turbulence, open-channel turbulence, water surface fluctuation, space-time image, PTV, STIV
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