Application Of The Discrete Particle Method And The Point Particle Immersed Boundary Method In The Study Of Sediment Transport

Sediment transport in three-dimensional turbulent flow is a typical two-phase flow problem. This paper numerically simulated the sediment transport by using a methodology which combines three cutting-edge numerical techniques, i.e., the coupled ‘event-driven' and ‘spring-dashpot' discrete particle modelling of the motions and collisions of millions, even tens of millions, of discrete particles, the ‘point-particle' immersed boundary method for the fluid-particle interaction and the direct numerical simulation or large eddy simulation of turbulent flows using a highly efficient parallel computing code named Cg LES. This methodology is suitable for simulations of large-scale sediment evolution and thus can be valuable from the engineering point of view.This paper numerically investigated three typical sediment transport phenomena including the motions and distributions of particles immersed in a turbulent boundary layer of channel flow, the evolution of sand ripples in a turbulent open channel flow and local scour around a circular pile. The main findings are presented as follows:The motions of particles have strong effects on flow velocity profiles and turbulence intensities, and are closely related to the dynamics of the near wall coherent flow structures. Most of inertial particles in the turbulent boundary layer reside preferentially in low speed fluid regions and form streamwise-aligned streaky structures. This preferential aggregation phenomenon is primarily governed by particles Stokes number and is more significant as the Stokes number approaches unity.The sand ripples can merge together in a turbulent open channel flow and their height increase approximately linearly when the ripple number is constant, while the mean value of their length is invariant. With the increasing sand ripple height, the sediment transport rate decreases gradually and reach a constant value eventually. However, when the sand ripples merge together, a rapid increasing was observed in the curve of their height, meanwhile a large drop in the transport rate was found.The local scour around a vertical circular pile starts from the position 40? from the symmetry plane of z axis, at which the scour depth keeps maximum though the whole process. As the scour pattern develops, the rate of scour decreases and the scour and the deposition regions extend downstream and finally reach an equilibrium state.