Particle–turbulence interaction and local particle concentration in sediment-laden open-channel flows

Abstract

The present study describes an experimental investigation on the effects of ejection and sweep motions to the local sediment concentration and turbulence modulation in suspended sediment-laden open-channel flows by using a combination between a discriminator particle tracking velocimetry (D-PTV) for sediment particles and a discriminator particle image velocimetry (D-PIV) for fluid tracers. Fluid tracers and sediment particles were discriminated by their occupied particle sizes, and the particle velocity and the fluid velocity were determined simultaneously. It is necessary to investigate coherent structure and particle–turbulence interaction in suspended sediment-laden open-channel flows for predicting the transport of suspended sediment in rivers. There are a lot of previous studies on velocity measurements and numerical simulations in these suspended sediment flows. However, there are little investigation on simultaneous measurements between particles and fluid in bursting phenomena of open-channel flow. So, this study focuses the particle–fluid interaction in the ejection and sweep events by using the discriminator PIV/PTV. The present study found that the turbulence in sediment-laden flows is enhanced or suppressed as compared with that of sediment-free (clear-water) flow. These enhancement and suppression of turbulence are determined by the critical particle diameter, which is correlated with the Kolmogoroff microscale rather than the macroscale of turbulence. The strength of the ejections and sweeps was changed by suspended sediment. The local sediment concentration became about 20–40% larger when the ejection motion occurred, whereas it became about 10–30% smaller when the sweep motion occurred.