Actas de congresos
Statistical Characterization of the Intermittency of Bedload Transport in Conditions Near the Threshold of Motion
Fecha
2015Institución
Resumen
The dynamics of sediment particles in a flat bed channel is mainly determined by near bed coherent
structures of the turbulent boundary layer. These vortices are characterized by intense velocity
fluctuations, which produce an instantaneous increase of the bed shear stress and consequently,
sediment particle entrainment and deposition. At low shear stress conditions, the sediment flux has
an intermittent behavior, with a series of frequent and localized transport events. Although many
experimental and computational investigations have addressed the interaction between the flow and
the sediment particles, the mechanisms that generate the intermittency in the bedload transport flux
are not yet fully understood. In order to give new insights into these processes, we develop a
Lagrangian sediment transport model to simulate sediment transport in a flat bed channel. We
couple direct numerical simulation (DNS) to solve the 3D NavierStokes
equations for the flow and
the discrete element method (DEM) to solve the particle dynamics (LIGGGHTS,
http://www.cfdem.com/liggghts), using a twoway
coupling approach. The objectives of this study
are: i) to make a detailed description of the firstorder
statistics of sediment particles, and ii) to
explore the intermittent nature of sediment transport in conditions near the threshold of motion. For
low Shields numbers, we show that this intermittency has a fractal behavior, whose characteristics
change as the shear stress increases