基于LBM-DEM耦合计算模型的含水层内悬浮颗粒运动特性

基于格子Boltzmann法(LBM)与离散单元法(DEM)的基本理论,通过对格子单松弛模型演化方程进行修正,建立LBM-DEM耦合计算模型。引入浸没移动边界方法(IMB),利用MATLAB开发LBM-IMB-DEM耦合求解程序,对悬浮颗粒在含水介质中的运动过程进行模拟计算。通过开展层析柱强制渗流试验,验证计算模型与求解方法的正确性,从孔隙尺度分析地下水动力、颗粒形貌和尺寸效应对含水层渗透性能的影响。结果表明,进口流速为5×10_^-5m/s时,含水层各区域的渗流速度均呈现下降、回升、稳定的三个连续阶段。将悬浮颗粒由球形硅微粉替换为非球形硅微粉后,各断面的平均流速最大降幅升高,恢复率降低。基于颗粒受力平衡分析,由于球形硅微粉转动惯量较低,易于脱离含水介质表面；非球形硅微粉多絮凝成团,迁移过程中出现沉积或被孔喉捕获的机率提高,并且沉积后难以发生再释放过程。随着渗流速度的降低与含水介质计算区域的增加,悬浮颗粒形貌的变化对于含水层水动力场演化过程的影响程度增强。

Study of Flow Characteristics of Suspended Particles in Aquiferwith Coupled LBM-DEM Numerical Model

A coupled LBM-DEM numerical model was developed by modifying Lattice Bhatnagar Gross Krook evolution equation based on the theory of lattice Boltzmann method (LBM) and discrete element method (DEM). While the immersed moving boundary method (IMB) was introduced, MATLAB was used to develop a LBM-IMB-DEM coupling solving program to simulate the movement of suspended particle in aquifer medium. Accuracy of the model and the solution method were verified by chromatographic column forced seepage experiment. The effects of groundwater dynamics, particle morphology and size effect on aquifer permeability were analyzed in porous scale. The results show that when the inlet velocity is 5×10_^-5 m/s, the seepage velocity in aquifer presents three successive stages of declining, rising and stabilizing. The maximum drop of the average velocity of each section increases and the recovery rate decreases after changing the suspended particle solution from spherical silica powder to non-spherical silica powder. According to the particle force balance analysis, spherical silica powders can be easily detached from the grain surface of the aquifer medium due to its low rotary inertia; since the flocculating lumping are often observed in non-spherical silica powders, the probability of the attachment in matrix surface or the captured by the pore throat are enhanced during transport, and it is difficult for non-spherical silica powders to re-release after deposition. While the seepage velocity decreases and the calculation area of the aqueous medium increases, the influence degree of suspended particle morphology on the hydrodynamic evolution of aquifer strengthens.