Author(s): Haoyin Shan; Kornel Kerenyi; Junke Guo
Linked Author(s): Junke Guo
Keywords: No Keywords
Abstract: Incipient motion of saltating sand under unsteady flow conditions is essential to understanding of scour processes during a flood event. A flume experiment was conducted under unsteady flow conditions by increasing velocity. The incipient motion of a 5 mm-diameter plastic particle, entrained from a bed composed of identical well-packed plastic particles, was used to model the movement of saltating sand. A high-speed camera with a 2000 frames per second (FPS) flash rate was utilized to record the particle's movement. The particle's trajectory was obtained by processing images captured with a LabVIEW program. It is clearly seen that at the moment of entrainment, the particle springs upward about 1 mm, then saltating downstream until it reaches a height of 1.1-1.7 times of diameter; the corresponding saltation length is about 5-11 times of diameter. The displacements in this rising phase were found to be well fitted by a cosine function for the vertical and a parabolic function for the horizontal. The particle's velocity, acceleration and eventually the lift were then derived, which is 1.4-1.8 times of a particle's submerged weight. The influence between particles was also analyzed.