多孔介质粒径变异系数对污染物运移的影响  

Effect of Coefficient of Variation of Particle Size of Porous Media on Contaminant Transport

作　　者：张建桥 窦智[1] 张学羿 Zhang Jianqiao;Dou Zhi*;Zhang Xueyi(School of Earth Sciences and Engineering,Hohai University,Nanjing 211100,China)

机构地区：[1]河海大学地球科学与工程学院,江苏南京211100

出　　处：《地球科学》2023年第9期3444-3453,共10页Earth Science

基　　金：国家重点研发计划项目(No.2019YFC1804303);国家自然科学基金项目(No.41877171).

摘　　要：多孔介质污染物运移对于明晰地下水污染很重要,但在多孔介质中粒径变异系数(coefficient of variation,COV)对内部微观孔隙结构中污染物运移过程影响的研究还存在不足.为此,基于随机算法,提出了一种不同COV且孔隙度一致的多孔介质几何模型构建方法,通过对Navier-Stokes(N-S)方程和对流‒扩散方程(advection-diffusion equation,简称ADE)进行耦合求解得到多孔介质地下水流场及污染物浓度场,引入克里斯琴森均匀系数,定量评价流场流速分布的均匀性,基于MIM(mobile and immobile)模型和ADE模型分析耦合求解得到的穿透曲线特征.结果表明:随着粒径COV的增大,流场流速分布的不均性增强,MIM模型中的溶质流动区域占比β、无量纲传质率α*均增大;MIM模型拟合优度高于ADE模型,且随COV增大,ADE模型的拟合全局误差Ei逐步增大.总体上,粒径COV控制了溶质流动区域和非流动区域的大小及其之间的溶质交换强度,造成了多孔介质内部溶质运移的“非费克”行为,使得ADE模型的误差逐步增大,对于较大COV的多孔介质,MIM模型具有更好的适用性.The contaminant transport in porous media is crucial for a comprehensive understanding of groundwater contamination.However,there are still inadequacies in the research concerning the effect of the coefficient of variation(COV)of particle size of porous media on the contaminant transport in the internal microscopic pore structure.A method is proposed to construct a geometric model of porous media with different coefficients of variation and consistent porosity based on a random algorithm.The groundwater flow field and contaminant concentration field in porous media are obtained by coupling the Navier-Stokes equation and the advection-diffusion equation.The uniformity of flow velocity distribution is evaluated quantitatively by introducing Christiansen uniformity coefficient.Based on the MIM(mobile and immobile)model and the ADE(advection-dispersion equation)model,the characteristics of breakthrough curves are analyzed.The results show that as the COV of particle size increases,the non-uniformity of the flow velocity distribution is enhanced.The COV of particle size is positively correlated with the ratio of solute mobile domainβand the dimensionless mass transfer rateα*;the goodness-of-fitting of MIM model is better than that of ADE model,and as the COV increases,the fitting global error Ei of ADE model gradually increases.Overall,the COV of particle size controls the size of mobile and immobile domain and solute exchange intensity between two domains,resulting in the non-Fickian behavior of solute transport in porous media.This also causes the error of ADE model gradually increases.MIM model has better applicability for the porous media with larger COV.

关 键 词：多孔介质 污染物运移 变异系数 穿透曲线 反演模型 地下水 

分 类 号：P641.69[天文地球—地质矿产勘探]