DEM Simulation And Experimental Research On The Characteristics Of Couette Particles Flow

In the natural world and human production and life,there are widespread particle flow phenomena such as avalanche,landslide,grain delivery and pharmaceutical processing.The particulate matter will exhibit different phases such as solid and liquid in the flow process.As a typical particle flow form,ring-shear particles have been highly concerned by researchers.The study of the physical and mechanical meso-mechanism of flow behavior and size separation is urgently needed to be research.In this paper,DEM(Discrete Element Method)numerical simulation analysis and experimental research are carried out for the characteristics of surface ring radial separation and size separation in classical ring shear particle flow.Develop DEM program in C++language and introduce CUDA(Compute Unified Device Architecture,a universal parallel computing architecture from NVIDIA)based GPU parallel technology.An experimental method for studying the size separation of Couette particle flow is proposed and an experimental device for rotating the outer cylinder is developed.The numerical simulation and the experimental results are in good agreement to verify the effectiveness of the Couette particle flow DEM program.Based on the advantages of the DEM mesoscopic parameters,the physical and mechanical mechanism of the flow characteristics of the Couette particles is further given.The main work of this paper is:(1)The DEM simulation program based on CUD A parallel optimization was developed to simulate the surface flow characteristics of Couette particle flow.The effects of different parameters such as the rotational speed of the outer cylinder and the thickness of the granular layer on the circumferential and radial motion of the surface particles are considered.The cross-section method is used to describe the internal movement trend of the particle flow and explain the flow characteristics mechanism.The results show that the angular velocity of the surface particle flow decreases exponentially with the decrease of the radial position.Radial separation occurs on the surface of the particle flow and there is a critical ring.The critical ring radius is proportional to the rotational speed of the outer cylinder and inversely proportional to the thickness of the granular layer at lower rotational speeds.The particle flow has a closed circumfluence in the thickness direction of the particle layer and a flow band directed obliquely upward to the inner cylinder,and the combined action of the two causes the radial separation of the surface of the particle flow.(2)The motion behavior of spherical objects in Couette particle flow is studied by DEM simulation program.Considering the influence of parameters such as the rotational speed of the outer cylinder,the size and weight of the spherical object,the thickness of the granular layer on the floating time of the object in the Couette particle flow,the mesoscopic parameters such as the upper and lower surface flow velocity and porosity are introduced to research the mechanical mechanism of object floating motion in Couette particle flow.The results show that the floating time of the object decreases as the rotational speed of the outer cylinder increases.And increases with the thickness of the particle layer and the weight of the object.During the ascent,the upper surface velocity of the object is always greater than the lower surface,and the difference in porosity between the upper and lower regions is always near the zero line.The lower region porosity curve indicates that the particles are lifted up and down by constantly filling the pores below the object.In addition,the annular convection originally existing inside the particle stream causes the upward movement of the object entering the region and is another important mechanism for the object to eventually float to the surface of the particle flow.(3)DEM simulation and experimental research on two-phase Couette particle flow with different particle sizes.The results obtained by the two methods are in good agreement,and there is a trend of uniform size separation.Under the particle ring shear flow,small particles ooze from the pores between the large particles and gradually occupy the space below,and the large particles are forced to float.It can be seen from the floating rate at different speeds that the faster the outer cylinder rotates,the larger the floating rate,that is,the higher the degree of separation.The Lacey mixing exponent curve and the large and small particle energy curves during the separation process indicate that there is a separation-mixing-separation process in the separation region,and the large particles do not have a fixed "upper channel" in the small particles.