(47b) CFD-DEM Study on Macro- and Microscopic Behavior of Binary Mixtures of Spheres Under Air Impact

This paper presents a numerical modeling on the packing densification of binary mixtures of spheres under air impact using a combined Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM). In the whole process, the structure evolution, force distribution and deviator stresses at different particle size ratios (PSR, PSR = 3, 5 and 7) are comprehensively studied. Macro- and microscopic properties such as packing density, coordination number and contact types, radial distribution function, forces and deviator stresses at different stages are characterized and compared. The results show that air impact can realize the transition of binary sphere packings with different PSR from random loose state to random close state under appropriate conditions. The normal force distributions indicate an exponential decay law for each binary packing, and the contact type between big and small particles gradually dominates the force distribution as the PSR increases. Meanwhile, the number of strong forces (larger than the average force in the whole packing system) decreases with the increase of the PSR, but increases as the result of air impact. Furthermore, the amount of small forces in the final packing after air impact is relatively less than that in the initial packing regardless of contact types. While most deviator stresses in the packing are negative due to the air impact, indicating that the contact forces tend to be orientated perpendicular to the direction of the applied deviator. The macro- and microscopic behavior of the packings upon the air impact can be used as theoretical references for the process in foundry and other engineering areas.