基于透明土技术的多孔介质孔隙流动特性研究

Pore flow characteristics of porous media based on transparent soil technology

土体作为一种特殊多孔介质,内部孔隙通道尺度与形态随机性强,导致土体渗流场中孔隙流速分布不均,即存在优势流现象。优势流是影响污染物运移、导致土体渗透变形的重要因素。基于透明土原理,利用聚丙烯酸钠交联聚合物颗粒和蒸馏水,配制成饱和透明多孔介质,并利用一种新的研究透明多孔介质内部流场的装置及方法,将绿色光源激光器、单反相机、十字滑台等组合成简易粒子图像测速(PIV)系统,采集不同水力梯度下透明多孔介质内部流场图像,结合粒子图像测速技术,将得到的流速数据进行统计分析,揭示孔隙液体的流动特性。研究表明,利用自制简易PIV系统进行流场测量,实测孔隙流动结果与宏观流速吻合程度高,能够实现对流场的多点、无扰、高精度测量。研究发现多孔介质内部纵断面上的孔隙面积与纵断面所在位置有关,而孔隙面积越大,断面上的孔隙流速也越大。多孔介质内部孔隙流速分布规律大致相同,优势流速随着断面流速的减小而减小,优势流速越小,其概率密度越高,优势流动现象越显著。

The soil is a kind of special porous medium, whose internal pore channel is extremely random. As a result, the pore velocity distribution is not uniform in its seepage field, which is referred to the preference flow phenomenon. The preference flow is an important factor influencing the pollutant migration and infiltration deformation of the soil. Based on the principle of transparent soils, the saturated transparent porous medium is mixed with sodium polyacrylate cross-linked polymer particles and distilled water. A simple particle image velocimetry (PIV) system is combined with a green light laser, a SLR camera and a cross slide to study seepage in transparent medium. The flow field images of transparent porous medium under different hydraulic gradients are collected, and the velocity data obtained are statistically analyzed by combining with the particle image velocimetry technology to reveal the flow characteristics of pore fluid. The results show that the measured results are in good agreement with the macroscopic velocities. The simple PIV system can be used to measure the flow field with multi-point, non-interference and high precision. It is found that the pore area in the longitudinal section of porous medium is related to the location of the longitudinal section, and the larger the pore area, the larger the pore flow velocity on the section. The distribution of pore velocity in porous medium is approximately the same. With the decrease of longitudinal section velocity, the preference velocity decreases. The smaller the preference velocity is, the higher the probability density is, the more significant the preference flow phenomenon is.