分形结构团聚体在流场中分散混合的数值模拟

Numerical Simulation of Dispersive Mixing in Flow Field of Particulate Agglomerates with Fractal Structure

为深入了解分散混合的机理及其动态细节,在经典离散元理论模型中引入范德华力和流体拖曳力,开发了二维颗粒离散元程序DEMix2D,对具有分形结构的颗粒团聚体在剪切、拉伸和剪切-拉伸混合流场中的分散混合过程进行数值模拟.模拟结果表明:团聚体在流场中先发生变形然后再分散,分散过程中存在剥蚀和破裂两种分散方式;流场强度相同时,团聚体在拉伸流场中的分散效率最高,碎片平均尺寸最小,在剪切流场中的分散效率最低,碎片平均尺寸最大;在相同形式的流场中,随着流场强度增加,团聚体的分散效率提高,碎片平均尺寸减小.

In this paper,a 2-D discrete element program Demix2D is developed to investigate the dispersive mixing mechanism and dynamic details of particulate agglomerates by introducing the van der Waals force and the fluid drag force into the classic discrete element model.Then,the dispersive mixing process of the agglomerates with fractal structure is numerically simulated in three different flow fields,namely,the steady shear flow field,the elongation flow field and the combined shear and elongation flow field.Simulation results show that （1） the agglomerates in the flow fields first exhibit deformation behavior and then disperse in the manners of erosion and rupture; （2） under the same flow stress,the elongation flow field has the highest dispersion efficiency with the smallest final average fragment size,while the shear flow field has the lowest dispersion efficiency with the largest final average fragment size ; and （3） with the increase of the flow stress in the same flow field,the dispersion efficiency increases and the final average fragment size decreases.