Discrete element modelling of grain size segregation in bi-disperse granular flows down chute

Abstract

Three-dimensional DEM simulations of size segregation in granular flows down chute are presented. Different cubic bi-disperse samples are generated by pluviation, on the rough base formed by randomly placed particles. Periodic boundaries are applied to the flow direction and the two sides. Parametrical studies involving slope angle, width, volume fraction, and coefficient of friction are systemically performed. In all presented cases, steady, fully developed (SFD) state is achieved, where the kinetic energy and fractional volume distribution remain constant. From the macroscopic view, segregations are completed in the SFD state with slightly different extents and a thick layer of pure coarse grains appears on the top of the flow. The profiles of volume fractions are calculated and presented by shear layers. In addition, the trajectories of individual particles are tracked and analysed, showing clearly the contact conditions and shear history experienced by individual particles. It is found that the connectivity of small particles is generally at a lower level than that of the large ones, indicating a high probability of small particles dropping into voids under gravity is higher. On the other hand, the large particles experience a significant increase of connectivity as they migrate through the layer of small particles.