An Eulerian two-phase model for steady sheet flow using large-eddy simulation methodology

• Published in: Advances in water resources Vol. 111; pp. 205 - 223
• Main Authors: Cheng, Zhen, Hsu, Tian-Jian, Chauchat, Julien
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-01-2018; Elsevier Science Ltd; Elsevier
• Subjects: Bed roughness; Computational fluid dynamics; Computer simulation; Contact pressure; Dilution; Dissipation; Drag; Ejection; Empirical analysis; Energy budget; Environmental Engineering; Environmental Sciences; Flow velocity; Fluid flow; Fluid mechanics; Interactions; Kinetic energy; Kinetic theory; Kinetics; Laminar flow; Large eddy simulation; Large eddy simulations; Mechanics; Multiphase flow; Near-bed intermittency; Oceanic eddies; Physics; Pressure; Reynolds stress; Sediment; Sediment concentration; Sediment transport; Sediments; Sheet flow; Simulation; Stratified flow; Thickness; Three dimensional flow; Three dimensional models; Transport; Turbulence; Two phase flow; Velocity; Velocity distribution; Viscosity; Vortices; Near-bed intermittency; Sheet flow; Two-phase flow; Large-eddy simulation; Sediment transport
• ISSN: 0309-1708; 1872-9657
• DOI: 10.1016/j.advwatres.2017.11.016

•A 3D LES Eulerian two-phase model is developed and validated for sediment transport in steady sheet flow.•For high Stokes number particles, the drag-induced turbulence damping is significant in the sheet flow layer.•The near-bed sediment intermittency is highly related to the turbulent ejection/sweep motions and mobile bed roughness.
A three-dimensional Eulerian two-phase flow model for sediment transport in sheet flow conditions is presented. To resolve turbulence and turbulence-sediment interactions, the large-eddy simulation approach is adopted. Specifically, a dynamic Smagorinsky closure is used for the subgrid fluid and sediment stresses, while the subgrid contribution to the drag force is included using a drift velocity model with a similar dynamic procedure. The contribution of sediment stresses due to intergranular interactions is modeled by the kinetic theory of granular flow at low to intermediate sediment concentration, while at high sediment concentration of enduring contact, a phenomenological closure for particle pressure and frictional viscosity is used. The model is validated with a comprehensive high-resolution dataset of unidirectional steady sheet flow (Revil-Baudard et al., 2015, Journal of Fluid Mechanics, 767, 1–30). At a particle Stokes number of about 10, simulation results indicate a reduced von Kármán coefficient of κ ≈ 0.215 obtained from the fluid velocity profile. A fluid turbulence kinetic energy budget analysis further indicates that the drag-induced turbulence dissipation rate is significant in the sheet flow layer, while in the dilute transport layer, the pressure work plays a similar role as the buoyancy dissipation, which is typically used in the single-phase stratified flow formulation. The present model also reproduces the sheet layer thickness and mobile bed roughness similar to measured data. However, the resulting mobile bed roughness is more than two times larger than that predicted by the empirical formulae. Further analysis suggests that through intermittent turbulent motions near the bed, the resolved sediment Reynolds stress plays a major role in the enhancement of mobile bed roughness. Our analysis on near-bed intermittency also suggests that the turbulent ejection motions are highly correlated with the upward sediment suspension flux, while the turbulent sweep events are mostly associated with the downward sediment deposition flux.