Fluid-driven transport of spherical sediment particles: from discrete simulations to continuum modeling

Empirical bedload transport expressions commonly over- or underpredict sediment flux by more than a factor of two, even under controlled laboratory conditions. In this work, the Discrete Element Method and Lattice Boltzmann Method are coupled together to simulate 3D fluid-driven transport problems, in which the spherical sediment particles are fully resolved. After comparisons with flume experiments are made to test the numerical simulations, the grain-scale physics is studied, such as the flow field around individual particles and higher order descriptions of the granular motion. A more robust continuum model, unifying empirical models under various conditions and in different regimes, is further proposed based on the new grain-scale understanding of the mechanisms.