  Barchans are crescent-shaped dunes commonly found in diverse environments and
scales: from the 10-cm-long barchans found under water to the 1-km-long
barchans on Mars, passing by the 100-m-long dunes on Earth's deserts. Although
ubiquitous in nature, there is a lack of grain-scale computations of the growth
and evolution of those bedforms. In this paper, we investigate the values of
grain properties (coefficients of sliding friction, rolling friction and
restitution) necessary to carry out numerical simulations of subaqueous
barchans with CFD-DEM (computational fluid dynamics - discrete element method),
and how the values of those coefficients change the barchan dynamics. We made
use of LES (large eddy simulation) for the fluid, varied the coefficients of
sliding friction, rolling friction and restitution in the DEM, and compared the
outputs with experiments. We show: (i) for the case of glass spheres, the
values of coefficients for correctly obtaining the dune morphology, timescales,
trajectories of individual grains, and forces experienced by grains; (ii) the
LES meshes allowing computations of bedload while capturing the main
disturbances of the fluid flow; (iii) how different values of coefficients
affect the morphology of barchans; and (iv) that spheres with higher
coefficients of rolling friction can be used for simulating barchans consisting
of angular grains. Our results represent a significant step for performing
simulations that capture, at the same time, details of the fluid flow (large
eddies) and grains' motion (individual particles).
