Semi-resolved LES–DEM simulations of turbulent bedload transport from saltation to sheet flow regimes

Bedload transport is ubiquitous in natural environments and encompasses flow regimes from saltation to sheet-flow, characterized by distinct fluid–particle interaction mechanisms. Accurately capturing these processes requires a numerical approach that can capture both turbulence and fluid-particle interactions, for which challenges exist due to the constraints of grid resolution on the coupling accuracy. In this study, we propose a semi-resolved LES–DEM framework to overcome such limitations in the conventional CFD-DEM paradigm. A feedback-controlled body-force term is also proposed to maintain a prescribed discharge under periodic boundary conditions in turbulent open-channel flow simulations. Three benchmark cases are conducted to assess the accuracy and robustness of the proposed framework, including clear-water turbulent channel flow as well as bedload transport in both saltation and sheet-flow regimes. The present method is demonstrated to effectively overcome the conventional grid-size limitation and thus allows the fluid field to be resolved on sufficiently fine grids while preserving accurate fluid-particle coupling. We further investigate the micromechanical processes underlying the transition from the saltation to sheet-flow regimes and quantify the thickness of the transport layers as functions of the Shields number. Overall, this framework provides a unified and reliable numerical tool for simulating sediment transport across a broad range of flow regimes, offering a solid basis for micromechanical analysis and the development of continuum models.