Author(s): Wang Dian-Chang
Linked Author(s): Dianchang Wang
Keywords: Flow visualization and image processing techniques; Turbulent open channel flow; Streak spacing; Streak width; Spatialstructure of low-speed streaks; Vortex model
Abstract: This paper presents an experimental study on the spatial structure of the low-speed streaks in the bottom region of turbulent open channel flows using flow visualization and image processing techniques. For the first time, variations of the spacing and the width of low-speed streaks with the Reynolds number based on shear velocity () were revealed. Test results show that the non-dimensional mean lateral streak spacing () is not a constant value of 100 widely accepted in previous publications. Instead, becomes larger as increases. In the smooth regime the spacing increases with the quadratic power of, but has a linear relationship with in the transitional regime. The variation of the width of the low-speed streaks with has a similar pattern to that of the spacing. The distribution of the streak width over the cross-section of the flume indicates that the width attains its maximum value at the central line and becomes narrower toward the side wall, and its distribution is symmetrical about the central line of the flume. The ratio of the streak spacing to the width is about 2.0. A new vortex model on the mechanism of streak formation is presented to explain the spatial structure of low-speed streaks.
Year: 2001