Résumé
The flow of granular matter is highly influenced by the properties of the constitutive grains. Among these properties,the shape is most likely one of the more influential. This is even more critical when the grain-shape is getting highlyconcave (e.g., star-shaped) since the packing properties exhibit non-trivial features like high porosity level andsharp jamming/unjamming transition. Despite the richness and ubiquitousness of these systems, very few is knownabout their flow behavior and the local mechanisms involved. By means of 2D Contact Dynamics simulations, weinvestigate the flow properties of strongly concave grains within a rotating drum. The system has the advantage ofpresenting, in a single test, almost all the flow characteristics that have been observed in granular systems: a solidto quasi-static and inertial flow phases. The shape of the grains is systematically varied from disks to crosses madeof four very thin arms. Rotation speeds are also varied, while making sure to remain in a dense and continuous flowregime with a well-defined free surface for all shapes. In general terms we find that, for a given rotation speed, theslope of the free surface increases with the concavity and then saturates at a certain grain concavity value. Thestress profiles vary significantly with grain shape, but still exhibit common generic trends. For example, the shearstress profile is characterized by an initial linear increase as the depth increases, then becomes independent of thedepth close the drum walls. On the contrary, the normal stresses decrease linearly with depth. Momentum balanceequations allows to correctly predict the normal stress profile for all shapes and drum velocities but fails in predictingthe shear stress profiles. By postulating that in the drum geometry annular regions of small thicknesses (analogousto the Couette shear) exist, we develop a new model that perfectly predict the shear stress profiles in a drum,whatever the shape of the grains and the rotational speeds