On turbulence closures for two-phase sediment-laden flow models

Abstract

Recent experimental studies show that there exists a difference between horizontal velocity components of particles and of fluid in sediment-laden open channel flows. For suspended particles with sufficient inertia, volume fraction profile cannot-be represented without the introduction of empirical parameters in passive scalar sediment transport models. The aim of this paper is to propose a two-phase model that allows representation of the main features of sediment-laden flows: the existence of a horizontal velocity difference between particles and fluid, the dispersion of particles by fluid turbulent motion, and the damping of fluid turbulent kinetic energy. A 2-D vertical numerical model for suspended particle transport in open channels using a two-phase approach is used in conjunction with experimental measurements. Different turbulence models for both phases are presented. The fluid phase turbulence is modeled by a k - ε model. Two models for the solid phase turbulence are used: a first-order model, based on the kinetic theory of granular flows, and an algebraic model based on an homogeneous, isotropic, and steady fluid turbulence assumption. We demonstrate that a modeling approach of the coupling between fluid and solid turbulence allows reproduction of the main features of sediment-laden flows. We show this approach represents an improvement compared with the classical approach. We show that a simple algebraic model based on the homogeneous, isotropic, and steady fluid turbulence assumption for the solid phase turbulence allows the physical phenomenon to be reproduced with very slight differences compared with a first-order model. Copyright 2008 by the American Geophysical Union.