On the incipient sediment suspension downstream of three-dimensional wall-mounted obstacles

Abstract

The incipient sediment suspension downstream of a thin square tab with various inclination angles was fundamentally described using experiments and theoretical arguments. Volumetric particle tracking velocimetry and particle image velocimetry were applied to measure the sediment particle distributions and wake flows under various incoming velocities and obstacle inclination angles. Results show that suspension of sediments occurred downstream of the obstacles due to the enhanced local turbulence intensities. Although the sediment volumetric fraction was mostly determined by the variation of wake turbulence kinetic energy under low inclination angles (i.e., obstacles nearly parallel to incoming flow), this was not the case under high inclination angle counterparts where distinct downward velocities dominated the wake region and suppressed the sediment suspension. This led to the decrease of sediment volumetric fraction with the growth of tab inclination at high inclination angles. Supported by flow measurements, a revised Rouse number was introduced which allows to quantitatively integrate the coupled influence of turbulence mixing load and vertical flows across various incoming velocities and inclination angles.