The present study focuses on the interaction between solid-particles and fluid in particle-laden open-channel flows. Turbulence measurements of both particles and fluid (water) were conducted by means of a discriminator particle-tracking velocimetry (PTV). The titanium compound polystyrene (specific density = 1.16 to 1.29, diameter = 0.39 to 1.18 mm) was used for solid-particles. In these experiments, the ratio between the particle scale and turbulence-length one was changed systematically. As the results, it was found that the particle velocity is larger than the fluid velocity in the near-wall region of y~+ ≤ 15, whereas the former is smaller than the latter in the region of y~+ > 15. This relative velocity between the particles and fluid increases with an increase of the particle diameter and specific density. The sweeps of particles near the wall become much larger than the ejections of particles as the diameter and specific density are larger. These facts suggest strongly that the particle motions may inrush towards the wall and transport high momentum to fluid.
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