LBGrain: An efficient multiscale lattice Boltzmann model for granular flows

We incorporate the Navier slip boundary condition into LBGrain, a multiscale lattice Boltzmann framework for granular flows, and validate its performance through comparisons with discrete element method (DEM) simulations. Rheological parameters of the granular flows are extracted from the coarse-grained results based on DEM data. Granular assemblies are treated as viscoplastic fluids, with their apparent viscosity governed by the regularized μ(I) rheology. A single-phase free-surface model is employed to track the fluid-gas interface. Navier slip boundary condition is introduced to quantify the basal slip of granular flows. Numerical validation of LBGrain is conducted through simulations of the periodic chute flow on an inclined plane, comparing with the reference data obtained from DEM. Results demonstrate an excellent agreement between the LBGrain velocity profiles and the theoretical Bagnold profiles extracted from the DEM data under varying inclination angles and flow depths, proving the accuracy of LBGrain. © The Authors, published by EDP Sciences, 2025.