A Semi‐Resolved LES‐DEM Framework for Turbulent Bedload Transport From Saltation to Sheet‐Flow Regimes

Abstract Bedload transport widely occurs in natural environments and encompasses flow regimes from saltation to sheet‐flow, with markedly different fluid‐particle interaction characteristics. Understanding these mechanisms requires a numerical tool capable of capturing both the turbulence and fluid‐particle interactions, for which challenges exist due to the constraints of grid resolution on the coupling accuracy. Here, we propose a semi‐resolved LES‐DEM framework to overcome such limitations in the conventional volume‐averaged 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 benchmarks are performed to examine the accuracy of the proposed framework, including clear‐water turbulent channel flow and bedload transport in both saltation and sheet‐flow regimes. The present method is demonstrated to avoid 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 explore the micromechanics and layerwise flow characteristics underlying the transition from the saltation to sheet‐flow regimes and identify the thickness of the transport layers as a function of the Shields number. This numerical framework offers a unified and reliable approach for simulating sediment transport across various flow regimes, providing a solid foundation for micromechanical investigations and the development of the continuum model.