Numerical Study of Near-Bed Turbulence Structures Influence on the Initiation of Saltating Grains Movement

Abstract

Abstract The focus of this paper is on the analysis of the influence of near-bed turbulence structures with the inclusion of existing coherent structures on the entrainment of saltating particles in a water stream from the Lagrangian perspective. The interactions between turbulence structures and initiation of particles movement is the key for better understanding of the physics of sediment transport and particles behaviour. These aims are addressed by use of a 3D relevant model of spherical saltating particles, in which a special procedure has been designed to produce coherent structures. In this method, the spectra of turbulent kinetic energy, consisting of four ranges, are used to generate the time series of turbulent velocities in the streamwise, vertical and transversal directions. Numerical results suggest that the initiation of sediment movement is strongly correlated to positive streamwise velocity fluctuations and as such, supports earlier laboratory experimental and field observations, showing that the sweeps and outward interactions play a crucial role in the initiation of saltating particles’ movement.