Large-Eddy Simulation of Erosion and Deposition over Multiple Two-Dimensional Gaussian Hills in a Turbulent Boundary Layer

We investigate the effects of one or more hills on the solid-particle saltation layer, and focus on the effect of the recirculation zone that plays an important role in solid-particle erosion or entrapment. The aerodynamic features of the flow have been presented previously (Huang et al. in Environ Fluid Mech 18:581–609, 2018) and the influence of hill separation was discussed in light of the classification deduced from the urban canopy scheme of Oke (Energy Build 11:103–113, 1988). Here, large-eddy simulations (LES) coupled with Lagrangian tracking of solid particles over multiple two-dimensional Gaussian hills in a turbulent boundary layer are performed using the atmospheric Advanced Regional Prediction System. Models for the interaction of particles with the soil are used, especially for take-off and rebound, and the boundary layer at different external velocities is first simulated. Numerical results are compared with experiments performed in our laboratory (Simoëns et al. in Procedia IUTAM 17:110–118, 2015) to collect particle concentration and velocity profiles, with the different forces acting on the particles at the wall analyzed. Accumulation and erosion zones are investigated regarding the shear velocity, and different fluxes as function of the Shields number are defined and discussed. Lower momentum transfer and exchange between the recirculation region and the mixing zone in the wake-flow regime result in an increase in the number of trapped particles compared with the skimming-flow regime.