Although the fluid invasion process impacts the transport and dispersion of chemicals and contaminants in the resident phase of natural, manufactured, and biological unsaturated porous media, these effects remain poorly understood. In this study, we investigate the role of hydrodynamic dispersion in different invasion patterns within the resident phase. While nonidealities in pore structures contribute to mechanical dispersion, our findings demonstrate that the interface front's morphology and the invading phase's distribution significantly influence mechanical dispersion within the resident phase.

Our results show that the complex distribution of the invading phase under unstable displacement greatly affects mechanical dispersion measures, such as velocity distribution, variance, and mean square displacement obtained through particle tracking. The interface also alters hydrodynamic dispersion measures, such as the local Peclet number, and generates extensive diffusion-dominated regions across the domain. This ultimately leads to solute trapping between pores that cannot reach the outlet. However, under stable invasion, mechanical and hydrodynamic dispersion do not deviate significantly from the reference saturated condition. In this scenario, dispersion anomalies occur within a short distance ahead of the moving interface, beyond which variations become similar to the reference media.

尽管流体侵入过程会影响化学物质和污染物在天然、人造和生物不饱和多孔介质的常驻相中的传输和分散，但人们对这些影响仍知之甚少。在这项研究中，我们研究了流体动力学扩散在驻留相内不同入侵模式中的作用。虽然孔结构中的非理想性有助于机械分散，但我们的研究结果表明，界面前沿的形态和侵入相的分布显着影响驻留相内的机械分散。

我们的结果表明，不稳定位移下侵入相的复杂分布极大地影响了机械分散测量，例如通过粒子跟踪获得的速度分布、方差和均方位移。该界面还改变了流体动力色散测量，例如局部 Peclet 数，并在整个域中生成广泛的扩散主导区域。这最终导致无法到达出口的孔隙之间的溶质捕获。然而，在稳定入侵下，机械和流体动力学扩散不会明显偏离参考饱和条件。在这种情况下，色散异常发生在移动界面前方的一小段距离内，超出该距离的变化变得与参考介质相似。