Numerical investigation on the incipient motion of non-spherical sediment particles in bedload regime of open channel flows

Abstract

Theoretical analysis and nowadays advanced numerical simulations for bedload particle transport widely share a popular assumption: All sediments are spherical and can be simplified as spheres, which apparently differs from reality. In order to explore the shape effects of sediment particles on their transport and to find out the possible consequence originated from the spherical assumption, a particle resolved computational model is established by combining the large eddy simulation for fluid and the discrete element method for the solid particles using an immersed boundary (IB) technique. Using this model, simulations are conducted for spherical and non-spherical bedload particles in both laminar and turbulent open channel flows. Simulation results show that shape of sediment particles has direct influence on the incipient motion in both laminar and turbulent flows. In laminar flows, the widely adopted spherical particles tend to exhibit over 5 times higher traveling speed compared with the non-spherical particles, and over 4 times longer time lag during incipient motion. In turbulent flows, the disk-shaped non-spherical particle yields up to 60% higher travel speed, 50% larger saltation height and 126% longer saltation length compared with spherical particles. The travel modes of non-spherical sediment particles during incipient motion are also analyzed.