非均质土柱中溶质迁移的连续时间随机游走模拟

非均质介质中溶质迁移往往出现非费克现象,传统的对流弥散方程(ADE)则难以较好地描述这种现象.采用连续时间的随机游走理论(CTRW)研究1250cm长一维非均质土柱中溶质运移问题,探讨CTRW模型中参数及非费克迁移的变化特征.研究结果表明,β值的大小与介质的非均质特征有关,非均质性越强,β值越小,但β值具有相对的稳定性,然而ADE的弥散系数则具有随尺度增大而增大的现象.对于介质非均质性较强和非费克现象较明显的溶质穿透曲线,尤其是在拖尾部分,与ADE相比,CTRW具有较高的模拟精度.

Modeling solute transport in heterogeneous soil column using continuous time random walk

Solute transport in heterogeneous media always occurs in the non-Fickian process with early arrival and long-tail. We analyze the data of the breakthrough curves(BTCs)measured in a 1 250 cm long heterogeneous soil column with the continuous time random walk(CTRW)and the advection-dispersion equation(ADE). It is found that Fickian behavior occurs in the transport at the distances from the inlet to 100 cm with a β value larger than 2,which is attributable to relatively homogeneous packing. Within the distances from 200 cm to 700 cm,the transport has significant non-Fickian behavior with β=0.915±0.024,this is due to the highly heterogeneity when packing the column. While the moderate non-Fickian transport isfound within the distances from 800 cm to 1200cm,and theβvalue is 1.19±0.0691 Compared with the dispersion coefficient of ADE,βvalue is relative stable. Better simulation results are also obtained especially for the tails of BTCs by using CTRW with respect to ADE. It implies that CTRW is a useful method to describe the scale-dependent transport and non-Fickian trans-port.