Granular Lubrication: Toward an Understanding of the Transition Between Kinetic and Quasi-Fluid Regime

Abstract

This paper is devoted to the understanding of flow characteristics of granular lubrication. The regimes of interest are: the kinetic regime in which collisions between particles are essentially binary and the quasi-fluid regime in which the duration of particle-to-particle contact is longer, primarily due to compaction. For this purpose, a quasi-two-dimensional particle dynamic simulation package is developed. The contact parameters between particles are chosen in order to mimic kinetic simulations. These contact laws are also valid in the quasi-fluid regime. The predictions of the particle dynamic simulations are compared to those obtained using the kinetic model. Good agreement between the two approaches is demonstrated. Furthermore, it is shown how the flow transition between the kinetic and the quasi-fluid regime can be determined. The influence of parameters that affect the transition is studied. The magnitude of the area fraction, on the order of about 90 percent of that of a hexagonal closest packing, seems to be the main factor that determines this transition.