Discrete simulations of fluid-driven transport of naturally shaped
sediment particles
Abstract
{A numerical scheme is developed to simulate the transport of natural
gravel. Starting with computerized tomographic (CT) scans of natural
grains, our method approximates the shapes of these grains by “gluing”
spheres of different sizes together with overlaps. The conglomerated
spheres move using a Discrete Element Method (DEM) which is coupled with
a Lattice Boltzmann Method (LBM) fluid solver, forming the first
complete workflow from particle shape measurement to high resolution
simulations with hundreds of distinct shapes. The simulations are
quantitatively benchmarked by flume experiments. The numerical tool is
used to further validate a recently proposed modified sediment transport
relation, which takes particle shape effects into account, including the
competition between hydrodynamic drag and material friction. Unlike a
physical experiment, our simulations allow us to vary the hydrodynamic
drag coefficient of the natural gravel independently of the material
friction. Our studies support the modified sediment transport relation.
The simulations also provide insights on the particle-level kinematics,
such as particle orientations, in the bedload transport process.
Particles below the bed surface prefer to orient with their shortest
axes perpendicular to the bed surface, but the tendency goes down as the
packing fraction decreases far from the bed surface. The particles
rotate freely in the dilute particle flow regime. }