(385f) Knudsen Boundary Layer in Granular Systems

The validity of the continuum hypothesis is often associated with the Knudsen number, which is the ratio of mean free path to a characteristic length scale. Hard-sphere, discrete-particle simulations of uniform particles were used to examine the effects associated with a local Knudsen number. The system is characterized by zero mean flow between two, impenetrable boundaries of constant granular temperature. In this work, the local Knudsen is defined according to the local packing fraction and the distance from the bounding wall. The departure from a strict continuum assumption is evident in the region near the bounding walls. The transition between the Knudsen boundary layer and the interior of the domain corresponds to the location where the reciprocal of the local Knudsen number is 2.5-5. The simulation results were compared with predictions from kinetic theory. The kinetic theory predictions are in better agreement with the simulations for dense systems in which the boundary effects are small.