基于Micro-PIV和LBM的土壤孔隙网络中流体速度分布表征

Characterization of Fluid Velocity Distribution in Porous-Network Micromodel based on Micro-PIV and Lattice Boltzmann Method

土壤孔隙结构复杂多变,揭示其内部流场特性对于描述和预测土壤中水分传输、溶质迁移等现象至关重要.基于规则性的土壤孔隙网络模型,采用Micro-PIV(Micro-scale Particle Image Velocimetry,显微粒子成像测速系统)技术分析不同雷诺数下孔隙结构中流体运动的特征,通过LBM方法(Lattice Boltzmann Method,晶格玻尔兹曼方法)对孔隙结构中流场分布进行数值模拟研究.结果表明:微观尺度下孔隙网络模型中不同孔隙区域流速分布差异明显,中线区域流场呈规律性分布,孔喉处为高速区,流速达到0.001 4 m/s,水平方向相邻两圆柱靠近边界处存在低速区,速度不高于0.000 2 m/s,在垂直于流向方向上速度场具有良好的对称性;靠近上下边界的大孔隙区域流体优先通过,流体的速度可达到0.003 0 m/s.LBM方法模拟的孔隙网络模型中流场分布结果与试验获得的流场分布吻合,其平均均方根误差为0.009 4 m/s,表明土壤孔隙网络模型能有效模拟土壤孔隙,捕捉微观尺度上的流体运动特征,为应用孔隙网络模型研究土壤孔隙中溶质运移和反应等问题提供了微观尺度的度量工具.

Revealing the characteristics of fluid flow is greatly important for describing and predicting soil water and solute transport in complicated porous soil media. A 2-D porous-network micromodel was developed to simulate the complex soil pore structure. Using micro-scale particle image velocimetry, the flow characteristics were studied by measuring the flow field under different Reynolds in porous-network micromodels, and the results were verified using Lattice Boltzmann Method.The results indicated that the microscopic velocities were discriminated in different porous-network locations.In the horizontal flow direction, the velocities in circumjacent pore throats （0.0014 m/s on average） were higher than those in other passageways.This was particularly true in the inner area of the adjacent cylinder （0.0002 m/s on average） along the flow direction in three typical pore spaces. In the vertical direction, the velocities were symmetrical along the central area, and the microscopic velocities near the top and bottom boundary areas could reach 0.0030 m/s. The LBM results were in agreement with the experimental outcomes, and the average root mean square error was above 0.0094 m/s. This indicated that the porous-network could accurately capture the microscopic flow characteristics modeling the soil pore structure. This study provides a new measurement method for studying solution transport and reaction process in the microfluidic pore network.