大颗粒与壁面碰撞的离散单元法模拟与分析

颗粒与壁面碰撞普遍存在于散体物料输送过程,研究颗粒与壁面碰撞有助于优化输送系统、减小物料磨损或提高输送经济性。本文基于离散单元法(DEM),采用Hertz-Mindlin无滑移接触模型,对单个6mm直径大颗粒与壁面碰撞进行了数值模拟和分析,研究了碰撞速度、碰撞角度和剪切模量对碰撞过程和法向最大接触力的影响。研究结果表明,Hertz-Mindlin无滑移接触理论描述的法向接触过程具有自相似特性,法向卸载时长与法向加载时长比值为定值。模拟的接触时长与Thornton等的关系式预测值相符。碰撞速度和碰撞角度对碰撞过程中的法向最大接触力均有明显影响,法向最大接触力随法向碰撞速度的增加近似线性增加;碰撞速度不变时,法向最大接触力随碰撞角度的增大而减小。剪切模量对法向接触力具有重要影响,在考虑颗粒磨损和破碎的DEM模拟时,不宜采用降低剪切模量加快计算速度。本研究对颗粒磨损和破碎研究以及高温气冷堆吸收球气力输送过程优化均具有重要意义。

DEM Simulation and Analysis of Collision between Single Coarse Particle and Wall

Particle-wall collisions widely exist in bulk solids transportation. Investigations on particle-wall collisions are helpful to optimize transporting system, decrease product attrition or improve transportation economy. Collisions between a single coarse particle (6 mm in diameter) and a wall were investigated by Hertz-Mindlin no-slip contact model based on discrete element method (DEM). Effects of impact velocity, impact angle and shear modulus on contact processes and maximum normal contact forces were studied. Results show that the normal contact process described by Hertz-Mindlin no-slip contact model shows self-similarity feature, and the ratio of unloading to loading duration in normal direction keeps as a certain value. The numerical contact durations agree well with the predictions by the correlation of Thornton et al. The impact velocity and impact angle show obvious effects on maximum contact forces. The normal maximum contact force increases almost linearly with normal impact velocity. For the certain impact velocity of 2 m/s, the normal maximum contact force decreases with the increase of impact angle. The shear modulus is a key factor to normal contact force, which suggests that speeding up DEM simulation by decreasing shear modulus should be avoided when particle attrition and/or breakage are in consideration. The results in the present study are important for investigation of particle attrition and/or breakage, as well as optimization of absorber sphere pneumatic conveying process in high temperature gas-cooled reactor.