Particle velocity and concentration profiles in bedload experiments on a steep slope

Abstract

Depth profiles of particle streamwise velocity, concentration and bedload sediment transport rate were measured in a turbulent and supercritical water flow. One‐size 6 mm diameter spherical glass beads were transported at equilibrium in a two‐dimensional 10% steep channel with a mobile bed. Flows were filmed from the side by a high‐speed camera. Particle tracking algorithms made it possible to determine the position, velocity and trajectory of a very large number of particles. Approximately half of the sediment transport rate was composed by rolling grains, and the other half by saltation. This revealed a complex structure, with several concentration and flux peaks due to rolling, and one peak due to saltation. With an increase of the sediment transport rate, the depth structure remained the same at the water/granular interface, with peak value increases but with no shift in elevations. The saltation region expanded towards higher elevations with an increase of the particle velocity commensurate to the water velocity. The proportion of the sediment transport rate in saltation did not vary significantly. The particle streamwise velocity profiles exhibited three segments: an exponential decay in the bed, a linear increase where rolling and saltation co‐existed, and above this, a logarithmic‐like shape due to saltating particles. These results are comparable to profiles measured and modelled in dry granular free surface flows and in more intense bedload such as sheet flows. Copyright © 2014 John Wiley & Sons, Ltd.

Investigation of vertical size segregation in bedload sediment transport with a coupled fluid-discrete element model

“…3 for both Shields numbers. An exponential decrease is observed in the quasi-static part of the bed [11] as evidenced on . According to this simple calculation, the fitted slope a appearing on Fig.…”

“…The model has been validated with turbulent bedload transport experiments, in terms of both the sediment transport rate and granular depth profiles. More details can be found in [7,11]. This model has also been used to analyse the dense granular rheology in turbulent bedload transport [12].…”

Cross-sectional imaging of refractive-index-matched liquid-granular flows

“…First, many experimenters have worked with opaque grains immersed in water or other transparent liquids, and simply focused on observing the flow behavior near transparent boundaries, leaving the internal flow unobserved (e.g., Sumer et al 1996;Capart et al 2002;Spinewine et al 2003Spinewine et al , 2011Armanini et al 2005;Capart and Fraccarollo 2011;Spinewine and Capart 2013). A second approach has been to work with narrow channels in which a single granular layer is held between parallel channel walls (Böhm et al 2006;Frey 2014). This makes the whole system observable, but reduces the threedimensional flow to a two-dimensional analog.…”

“…To capture both liquid and granular velocities, various researchers have seeded the liquid with tracer particles and used PTV and/or PIV to capture both the tracer and grain velocities (Hsu and Capart 2007;Mouilleron et al 2009;Spinewine and Capart 2013;Aussillous et al 2013). Simultaneous measurements of the solid fraction, on the other hand, have been deduced from ratios of granular area to total area, for laser-illuminated cross sections or monolayers (Chi 2007;Frey 2014), or from distance-to-wall statistics acquired using a laser stripe, for near-wall flows of opaque grains (Spinewine et al 2011;Capart and Fraccarollo 2011). Simultaneous velocity and concentration measurements have also been acquired by MRI and acoustic methods (Ovarlez et al 2006;RevilBaudard et al 2015).…”

“…Simultaneous velocity and concentration measurements have also been acquired by MRI and acoustic methods (Ovarlez et al 2006;RevilBaudard et al 2015). Whether acquired by optical or other techniques, the resolution of the velocity and concentration measurements has so far been limited to scales greater than the grain diameter, except for special circumstances like monolayers (Frey 2014) or systems composed of only a few large spheres (Hsu and Capart 2007).…”