Abstract
The lattice Boltzmann method is employed to conduct direct numerical simulations of turbulent open channel flows with the presence of finite-size spherical sediment particles. The uniform particles have a diameter of approximately 18 wall units and a density of ρp=2.65ρf, where ρp and ρf are the particle and fluid densities, respectively. Three low particle volume fractions ϕ=0.11%, 0.22%, and 0.44% are used to investigate the particle-turbulence interactions. Simulation results indicate that particles are found to result in a more isotropic distribution of fluid turbulent kinetic energy (TKE) among different velocity components, and a more homogeneous distribution of the fluid TKE in the wall-normal direction. Particles tend to accumulate in the near-wall region due to the settling effect and they preferentially reside in low-speed streaks. The vertical particle volume fraction profiles are self-similar when normalized by the total particle volume fractions. Moreover, several typical transport modes of the sediment particles, such as resuspension, saltation, and rolling, are captured by tracking the trajectories of particles. Finally, the vertical profiles of particle concentration are shown to be consistent with a kinetic model.
Highlights
Sediment transport is common in rivers, lakes, estuaries, and seacoasts
The inception motion of sediment particles in a recirculating flume was examined by Dwivedi et al [4], and their results revealed that the inception was highly correlated with strong sweep flow structures for both shielded and exposed particles
It is clearly observed that the streamwise velocity is reduced by the presence of particles, which is consistent with the results reported in particle-laden turbulent pipe flows [15]
Summary
Sediment transport is common in rivers, lakes, estuaries, and seacoasts In these hydraulic systems, the flow regime is turbulent. The spherical hydrogel particles had a diameter of approximately 9% of the channel depth and were slightly denser than the fluid Their results showed that the turbulent activities were damped near the wall by the particles; in the outer region of the flow, the sweep and ejection motions of the turbulence were enhanced. Righetti and Romano [3] studied a closed-circuit rectangular Plexiglas open channel with glass spheres (ρ p /ρ f = 2.6) of two different sizes (mean diameters at 100 μm and 200 μm) They reported that the particle mean streamwise velocity was smaller than its fluid counterpart except for particles that resided very close to the wall. The inception motion of sediment particles (mean diameter ranges from 20.8 mm to 83.2 mm) in a recirculating flume was examined by Dwivedi et al [4], and their results revealed that the inception was highly correlated with strong sweep flow structures for both shielded and exposed particles
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