Mechanism Analysis Of Polydispersed Shear Flows Of Cylindrical Particles Based On DEM

Some granular materials such as biomass fuel pellets and active pharmaceutical ingredients(APIs)have large particle aspect ratios.These elongated particles can be broken into short ones subject to large external forces.As a result,the granular material appears polydispersed with different particle aspect ratios.The aim of this paper is to study the cylindrical granular shear flow in a volume constant domain by numerical simulation based on the Discrete Element Method(DEM).The effects of particle size difference,particle concentration,size distribution and particle physical parameters on the flow behavior and constitutive law were studied in two types of particle systems(with friction and without friction),then it provides theoretical basis for complex particle problems in the industrial production(such as aerospace,pharmaceutical,hydropower and other fields).In this thesis,we only focus on the shear flows of polydispersed cylindrical particle mixtures,and the breakage of particles is not considered in the flow processes.The main contents include:(1)Firstly,in the frictionless granular shear flow,simulations are performed to investigate shear flows of binary and Gaussian distributions.In the binary granular system,the normalized stresses decrease as the volume fraction of larger aspect ratio particles(C)increases in the mixture.The stresses of a binary mixture are bounded by those of the monodispersed systems of two particle species.For the Gaussian distribution systems,the effect of standard deviation of particle aspect ratio on the stresses is limited.Meanwhile,the orientational alignment of larger AR particles is reduced and the alignment of smaller AR particles is increased in a mixture compared to the alignment of their monodispersed systems because of the interaction of different particle species in a mixture.(2)Secondly,in the frictional granular system,simulations are performed to investigate shear flows of monodispersed,binary and continuous distributions.As the granular flow transfers from inertial regime to elastic regime,there is a critical solid volume fraction and the stress surges rapidly with intense stress fluctuation.In the monodispersed,binary,and continuous granular flow,the critical volume fraction will decrease with the increasing average aspect ratio.Meanwhile,in the granular systems with a similar average aspect ratio,the critical volume fraction is larger in a system with a higher polydispersity.