Granular behavior in bedload transport using an Eulerian-Lagrangian model

Event details
Date | 10.03.2016 |
Hour | 12:15 › 13:00 |
Speaker | Dr Raphaël Maurin, ALEA team, IRSTEA, Grenoble |
Location | |
Category | Conferences - Seminars |
Turbulent bedload transport is studied considering idealized steady uniform configurations with monodisperse spherical particles. Focusing on the granular phase description, a coupled fluid-discrete element model is presented and validated with experiments. The model is used to analyze the influence of slope variation on bedload transport. The latter is classically taken into account as a variation of the critical Shields number resulting from the modification of the gravity contribution on the granular phase. Performing simulations by varying the channel inclination angle and the specific density, the sediment transport rate is observed to vary unexpectedly with both parameters.
An analysis of the continuous two-phase flow equations allows us to identify the origin of the different effects observed, and shows that the impact of the slope variation on the fluid flow inside the granular bed cannot be neglected. The latter is responsible for the transition from bedload to debris flow-like behavior and affects importantly the transport rate at high slope and/or low specific density. A rescaling of the Shields number is proposed from the equations and is shown to make all the data collapse onto a master curve when considering the dimensionless sediment transport rate as a function of the modified Shields number. Therefore, the latter characterizes well the slope influence on bedload transport and opens perspectives for a better understanding of the field observations.
An analysis of the continuous two-phase flow equations allows us to identify the origin of the different effects observed, and shows that the impact of the slope variation on the fluid flow inside the granular bed cannot be neglected. The latter is responsible for the transition from bedload to debris flow-like behavior and affects importantly the transport rate at high slope and/or low specific density. A rescaling of the Shields number is proposed from the equations and is shown to make all the data collapse onto a master curve when considering the dimensionless sediment transport rate as a function of the modified Shields number. Therefore, the latter characterizes well the slope influence on bedload transport and opens perspectives for a better understanding of the field observations.
Practical information
- Informed public
- Free
Organizer
- Christophe Ancey
Contact
- Christophe Ancey