| I present event-driven simulations of the interaction of a dense stream (volume fraction 0.65) of hard smooth disks with a circular obstacle. Both “slip” and “no-slip” boundary conditions at the obstacle are studied. First, a reference “elastic” case is investigated for Mach numbers from 0.02 to 0.3 (corresponding to Reynolds numbers from 3 to 46). In simulations of slower flows, the temperature and density are nearly homogeneous. In the case of no-slip boundary conditions, the flow patterns show the presence of eddy-like structures formed and shed irregularly and asymmetrically during the run. For slip boundary conditions, the corresponding simulations show a “waving tail” pattern behind the obstacle. For faster flows, in the no-slip case the patterns change to high-intensity regularly-shed swirls, likely caused by large temperature and density variations. In the slip case, these swirls are present only at the initial stages of the flow development.; Introduction of inelasticity into the system leads to very fast cooling, and the flow patterns show a transition to a shock development phase. It is shown that the friction-like (no-slip) interaction between particles and the obstacle is essential for the formation of a “static dune”, while the absence of friction between the particles themselves did not prevent the dune from forming. To investigate an inelastic case in the presence of an energy source compensating a loss of fluctuational energy due to inelastic collisions, an adaptation of a well-known stochastic thermostat model is used to establish a regime which avoids the suppression of flow patterns. It is shown that the granular medium driven in this way can exhibit flow patterns similar to those observed in non-driven systems of elastic particles, i.e., eddy-like structures and a waving tail, with no-slip and slip boundary conditions, respectively. |
