Bridging the gap between particle-scale forces and continuum modelling of size segregation: application to bedload transport

Gravity-driven size segregation is important in mountain streams where a wide range of grain sizes are transported as bedload. More particularly, vertical multi-scale process that originates interactions at the scale particles with morphological consequences on reach scale. To address this issue, volume-averaged multi-phase flow model for immersed bidisperse granular flows was developed based an interparticle force (Guillard et al. 2016) and Stokesian drag (Tripathi Khakhar 2013). An advection-diffusion derived from yielding parametrisations advection diffusion coefficients interactions. This approach makes it possible to bridge gap between grain-scale physics continuum modelling. Both models were successfully tested against existing Discrete Element Model (DEM) simulations bedload transport (Chassagne 2020). Through detailed investigation forces, demonstrated observed scaling inertial number can be explained by dependency viscosity. The coefficient shown linearly dependent small particle concentration. relationship friction confirmed additional non-trivial dependencies including concentration identified. Lastly, adding ratio perfectly reproduces DEM results large concentrations size-ratios.