Experimental study and numerical simulation of fluvial dynamics and sediment transport in instationary flow conditions

Abstract

Flows carrying bottom materials have a wide range of possible applications, especially in the technological and natural fields (Benaissa, Eléments de mécanique des sols. OPU, 1993). These flows that are loaded with granular materials are transport phenomena with diverse and complex mechanisms. They are characterized by the suspension of particles by turbulence, vertical density and velocity profiles, and deposition/erosion processes on the bottom of natural channels as the flow passes. The objective of this research is to experiment with the effects of the rough bottom (Recking, Etude expérimentale de l'influence du tri granulométrique sur le transport solide par charriage, 2006) on the dynamic behaviour of flows carrying solid particles of varying size, to study the behaviour of solid transport under the influence of certain easily accessible parameters, and, finally, to describe, as far as possible, the interactions between the solid particles and the water flow. These flows, responsible for sediment transits, are generally described by: Reynolds number (turbulence intensity), Stokes number (particle inertia), Rouse number, and Froude number (gravity effects). The equations governing the dynamics of particles in turbulence are complex (Gatignol, Journal De Mécanique Théorique Et Appliquée 2:42, 1983; Maxey and Riley, Phys Fluids 26:883, 1983). Most models rely on many simplifications and empirical corrections when the particle Reynolds ${\mathrm{R}}_{\mathrm{ep}}=\frac{\left({U}_{f}-{U}_{p}\right)d}{\nu }$ is very high. Experimental studies are therefore always necessary to get around this pitfall. This study is part of a project which consists in evaluating the effects of a rough bottom on the dynamic behaviour of flows carrying solid particles of variable size on a reduced model of a tiltable channel at the Hydraulics Laboratory of the University of Batna 2. The particles are entrained by a fast, turbulent, and supercritical liquid flow. It also consists in numerically simulating the flow of a mixture of fluid and solid particles in a rectangular channel to understand the interactions between the particles and the carrier phase. The study on the laws of friction in river beds aims at evaluating the impact of flows on the materials constituting the bottom of natural channels. The results obtained by simulation using the CLIPPER.5 program and PCA (Principal Component Analysis) are compared with the experimental results from the University of Batna 2. A good agreement is observed between the experimental values and those calculated during the simulation for high Re numbers.