基于CFD-DEM的非球形颗粒水力输送数值模拟

砂土等常见岩土颗粒系统在高速流动状态下具有显著的非稳态特征,其剪切速度分布与速度波动特征等均表现出显著的随机性。但目前颗粒系统细观特征对其宏观流动参数的影响尚不明确,针对岩土颗粒流动过程随机性特征参数的研究亟待加强。本文通过离散元环剪单元实验模拟,捕捉不同形状颗粒系统高速剪切流动过程中的宏微观特征。研究结果表明：(1)颗粒形状对系统宏观剪应力有较为显著的影响。颗粒长细比越大,其残余剪应力越大;(2)颗粒系统速度波动的空间分布同时受到剪切速度与边界效应两方面的影响。剪切速度越大,速度波动越大。边界对于颗粒速度波动具有一定的约束效应;(3)颗粒形状对系统速度波动大小有显著影响。颗粒越细长,微观速度波动越小;(4)形状特征对颗粒系统细观接触特征有显著影响。颗粒越细长,其平均配位数越大,出现较大粒间接触力的概率越小。

Self-diffusion scalings in dense granular flows

Under high-speed flow,sand,and other typical particle systems exhibit significant unpredictability in their shear velocity distribution and velocity fluctuation characteristics. However,it is currently unclear how the mesoscopic properties of granular systems affect their macro flow parameters,and there has been no thorough investigation into the stochastic characteristic parameters of particle flow. In this study,the discrete element ring shear element experiment is employed to capture both the macro and micro properties of the high-speed shear flow of particle systems with various forms. The findings demonstrate that:(1)Particle shape has a significant effect on the macroscopic shear stress of the system. The shear residual stress is larger in the particle system with a complex particle shape. (2)The spatial distribution of velocity fluctuation of the particle system is affected by both shear velocity and boundary effect. The greater the shear rate,the greater the velocity fluctuation. The boundary has a certain constraint effect on particle velocity fluctuation. (3)Particle shape has a significant effect on the velocity fluctuation of the system. For particles with more complex shapes,the system microscopic velocity fluctuation is small. (4)The shape characteristics have a significant influence on the meso-contact characteristics of the particle system. The longer the particle is,the larger the average coordination number is,and the smaller the probability of large intergranular contact force is.