Sediment Transport Induced by Coherent Structures in a Cylinder Wake: A CFD–DEM Study

Coherent structures generated in bluff-body wakes significantly influence particle motion near boundaries, affecting sediment transport and erosion processes. Conventional sediment transport models based on averaged shear stress or Shields parameter often fail to capture the unsteady, localized particle interactions dominant in regions with strong vortex shedding. In this study, high-resolution CFD-DEM simulations are performed to examine how coherent turbulent structures influence particle entrainment, saltation, and deposition patterns downstream of a cylinder. The CFD solver (OpenFOAM) employs a Large-Eddy Simulation (LES) to resolve coherent turbulent motions, while the DEM solver (LIGGGHTS) models detailed particle dynamics, including fluid-particle interaction and collision dynamics, via the CFDEM®coupling framework. Correlations between coherent vortical structures and particle motion were examined using spatial-temporal analyses of vorticity fields, Q-criterion, particle trajectories, and instantaneous particle velocities. Results indicate that conventional sediment transport models based solely on mean shear stress or Shields parameters have limitations in capturing the effects of coherent wake structures, highlighting the importance of explicitly incorporating unsteady wake turbulence and coherent vortices in modeling sediment dynamics. Complex particle trajectories—including occasional upstream motions, lateral displacements, and recirculation—were revealed through detailed analysis of instantaneous displacement vectors. These results highlight the need to incorporate coherent structures to capture such complex particle motions.