Events
PARTICLE CLUSTERING IN GRANULAR FLOWS: HYDRODYNAMIC SINGULARITIES IN A BOX OF SAND
An assembly of inelastically colliding hard spheres - the granular gas - is a simple model of flow of granular materials. It provides a fascinating example of a complex system far from
equilibrium. Granular gases exhibit a spontaneous clustering
instability: development of clusters of particles, and voids between them. A linear stability analysis of this system, employing a hydrodynamic description, was performed in the nineties, but nonlinear theory of this instability was a major unresolved problem.
We simplified this problem by considering a channel geometry, so that the coarse-grained flow is one-dimensional. We found that, when described by idealized hydrodynamic equations, the freely cooling granular gas exhibits a finite-time density blowup. This "attempted" singularity is usually arrested only when the close packing density of hard spheres is reached. In one limit of the instability, the dynamics is describable by a zero-viscosity Burgers equation which makes this system a distant cousin of a structure forming expanding Universe.