Particle distribution and energy transfer in sediment transport: a particle-resolved-simulation study

In sediment transport on a mobile erodible bed, near-bed particles tend to preferentially locate under specific flow regions and form an uneven bedform. These moving and mobile particles can significantly modulate turbulence at various scales, from inertial large-scale motions to small viscous motions. This study analyzes the particle-resolved direct numerical simulation data of particle-laden two-phase flow with multilayers of particles in turbulent flows over static and mobile beds. The double-average method is adopted for energy transfer analysis. The result shows that the alternative streaky bedform in the spanwise directions correlates with the streak structures in the near-wall turbulence in the mobile bed case. The energy redistribution and exchange, as well as the dissipation, are analyzed in detail, and an energy transfer diagram is given in the last to summarize the energy transfer processes. In both the static and mobile bed cases, flow energy is introduced into the system via the work performed by volume forces acting on the mean flow. The viscous dissipations in the double mean and form-induced fields are more pronounced in the static bed case, and the work done by the fluid-particle interfacial stress in the double mean and turbulent fields is more pronounced in the mobile bed case. The prominent energy contribution in the form-induced field is the production by the form-induced stress on the mean strain in the mobile bed case. In addition, sediment transport involving a limited number of mobile particles is insufficient to capture the energy transfer processes that occur over the troughs and may intertwine the energy transfer processes over the mobile particles and the fixed particle bed.