Viscoelastic flows through porous media become unstable and chaotic beyond critical flow conditions, impacting widespread industrial and biological processes such as enhanced oil recovery and drug delivery. Understanding the influence of the pore structure or geometry on the onset of flow instability can lead to fundamental insights into these processes and, potentially, to their optimization. Recently, for viscoelastic flows through porous media modeled by arrays of microscopic posts, Walkama et al. [D. M. Walkama, N. Waisbord, J. S. Guasto, Phys. Rev. Lett. 124, 164501 (2020)] demonstrated that geometric disorder greatly suppressed the strength of the chaotic fluctuations that arose as the flow rate was increased. However, in that work, disorder was only applied to one originally ordered configuration of posts. Here, we demonstrate experimentally that, given a slightly modified ordered array of posts, introducing disorder can also promote chaotic fluctuations. We provide a unifying explanation for these contrasting results by considering the effect of disorder on the occurrence of stagnation points exposed to the flow field, which depends on the nature of the originally ordered post array. This work provides a general understanding of how pore geometry affects the stability of viscoelastic porous media flows.

通过多孔介质的粘弹性流在超出临界流动条件时变得不稳定和混乱，影响广泛的工业和生物过程，例如提高石油采收率和药物输送。了解孔隙结构或几何形状对流动不稳定发生的影响可以使人们对这些过程有基本的了解，并有可能对其进行优化。最近，对于通过微观柱阵列建模的多孔介质的粘弹性流，Walkama 等人。[DM Walkama，N. Waisbord，JS Guasto，物理学。莱特牧师。124, 164501 (2020)]证明几何无序极大地抑制了随着流速增加而产生的混沌波动的强度。然而，在这项工作中，无序仅应用于一个最初有序的帖子配置。在这里，我们通过实验证明，给定一个稍微修改的有序帖子数组，引入无序也可以促进混沌波动。我们通过考虑无序对暴露于流场的驻点出现的影响，为这些对比结果提供了统一的解释，这取决于最初有序柱阵列的性质。这项工作提供了对孔隙几何形状如何影响粘弹性多孔介质流稳定性的一般理解。