title: Clustering and flow around a sphere moving into a grain cloud.
abstract: A bidimensional simulation of a sphere moving at constant velocity into a cloud of smaller spherical grains far from any boundaries and without gravity is presented with a non-smooth contact dynamics method. A dense granular "cluster" zone builds progressively around the moving sphere until a stationary regime appears with a constant upstream cluster size. The key point is that the upstream cluster size increases with the initial solid fraction [Formula: see text] but the cluster packing fraction takes an about constant value independent of [Formula: see text]. Although the upstream cluster size around the moving sphere diverges when [Formula: see text] approaches a critical value, the drag force exerted by the grains on the sphere does not. The detailed analysis of the local strain rate and local stress fields made in the non-parallel granular flow inside the cluster allows us to extract the local invariants of the two tensors: dilation rate, shear rate, pressure and shear stress. Despite different spatial variations of these invariants, the local friction coefficient μ appears to depend only on the local inertial number I as well as the local solid fraction, which means that a local rheology does exist in the present non-parallel flow. The key point is that the spatial variations of I inside the cluster do not depend on the sphere velocity and explore only a small range around the value one.
authors.affiliation: Laboratoire FAST, Université Paris-Sud, CNRS, Université Paris-Saclay, F-91405, Orsay, France. antoine.seguin@u-psud.fr.|SPEC, CEA, CNRS, Université Paris-Saclay, F-91191, Gif-sur-Yvette, France. antoine.seguin@u-psud.fr.
authors.forename: A
authors.initials: A
authors.lastname: Seguin
authors.affiliation: CMAP, CNRS, Ecole Polytechnique, Université Paris-Saclay, F-91128, Palaiseau, France.
authors.forename: A
authors.initials: A
authors.lastname: Lefebvre-Lepot
authors.affiliation: LMO, CNRS, Université Paris-Sud, Université Paris-Saclay, F-91405, Orsay, France.
authors.forename: S
authors.initials: S
authors.lastname: Faure
authors.affiliation: Laboratoire FAST, Université Paris-Sud, CNRS, Université Paris-Saclay, F-91405, Orsay, France.
authors.forename: P
authors.initials: P
authors.lastname: Gondret
keywords: Flowing Matter: Granular Matter