A general description of interphase interactions in Reynolds-averaged Euler-Lagrange simulations of turbulent sediment transport: from bedload to suspended load

Sediment transport in turbulent flows is one of the classical topics in rivers and coastal engineering studies. Due to a lack of general description of interphase interactions, the numerical studies are limited by separately describing the motion of sediment particles in the form of bedload or suspended load depending on the relative importance of particle-particle and particle-turbulence interactions. In this paper, a Reynold-averaged Euler-Lagrange model is developed to study bedload and suspended load simultaneously where the interphase interactions are described in a unified mechanical framework. The inter-particle interactions are resolved and the flow turbulence is described by a modified two-phase k-epsilon turbulence model. Particle-fluid interactions at the volume-averaged scale are characterized by the drag force, the pressure gradient force and the lift force. The effects of the interstitial fluid on particle contacts are taken into consideration by formulations of coefficient of restitution and friction coefficient. A modified Continuous Random Walk (CRW) model is adopted to characterize the stochastic motion of the sediment particles. The effectiveness of the model in describing particle-turbulence and particle-particle interactions is firstly demonstrated by comparison with experiments of sediment transport in bedload and suspended load separately. The model is further applied to the study of sediment transport in sheet flows. Contributions of particle-turbulence and particle-particle interactions to the flow structure, the total transport rate and the rheology of particle-fluid mixtures are analyzed.