The presence of surfactants in the unsaturated zone is one of the scenarios where the flow depends on the solute concentration. The simulation of flow and transport of surfactants requires the coupling of flow and transport, where the surfactant concentration-dependent changes to water retention (i.e. changes in surface tension and/or contact angle) and hydraulic conductivity need to be considered. This research presents a numerical experiment that compares surfactant flow and transport under intermittent boundary conditions to that of a conservative tracer. A modified version of Hydrus 2D, with the concentration-dependent surface tension and viscosity effects, is used. The numerical experiment examines the effect of surfactant infiltration, redistribution and flushing in a low-water content unsaturated porous medium with a deep water table. The numerical experiment encompasses not only the hysteresis as a result of transient localised drainage and rewetting associated with the surfactant-induced pressure gradients, and the intermittent boundary conditions. The comparison of surfactant flow to that of a conservative tracer indicates significant differences for the same boundary conditions. The results from this experiment will be beneficial for the design and optimisation of infiltration galleries employing surfactants for soil and ground water remediation, as well as for the understanding the flow and transport of grey water in the unsaturated zone.

中文翻译：

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渗流带中表面活性剂的流动和迁移：数值实验

在不饱和区中存在表面活性剂是流量取决于溶质浓度的情况之一。表面活性剂的流动和传输的模拟需要流动和传输的耦合，其中需要考虑表面活性剂的浓度依赖于保水性的变化（即表面张力和/或接触角的变化）和水力传导率。这项研究提出了一个数值实验，比较了间歇性边界条件下表面活性剂的流动和运输与保守示踪剂的流动和运输。使用Hydrus 2D的改进版本，具有浓度依赖性的表面张力和粘度效应。数值实验研究了在具有深水位的低水含量不饱和多孔介质中表面活性剂渗透，再分布和冲洗的影响。数值实验不仅包括由于与表面活性剂引起的压力梯度有关的瞬时局部排水和再润湿而产生的滞后现象，还包括间歇性边界条件。表面活性剂流量与保守示踪剂流量的比较表明，在相同的边界条件下存在显着差异。该实验的结果将有助于设计和优化采用表面活性剂进行土壤和地下水修复的渗入廊道，并有助于理解非饱和区中灰水的流动和输送。表面活性剂流量与保守示踪剂流量的比较表明，在相同的边界条件下存在显着差异。该实验的结果将有助于设计和优化采用表面活性剂进行土壤和地下水修复的渗入廊道，并有助于理解非饱和区中灰水的流动和输送。表面活性剂流量与保守示踪剂流量的比较表明，在相同的边界条件下存在显着差异。该实验的结果将有助于设计和优化采用表面活性剂进行土壤和地下水修复的渗入廊道，并有助于理解非饱和区中灰水的流动和输送。