We present an experimental study of a two-dimensional liquid foam, composed of a confined monolayer of bubbles, forced to flow within a model porous medium that mimics an inhomogeneous open fracture. It consists of a Hele-Shaw cell with a single localized constriction-like defect that reduces locally its gap and thus its permeability. Taking advantage of the possibility to directly visualize and follow the bubbles, we compute the bubble velocity field by image correlation analysis, as well as the bubble deformation field, through eccentricity measurements obtained by fitting each bubble with an ellipse. The defect acting as a permeable obstacle can strongly disturb the foam flow; we investigate here the influence of its geometry (height, size, and shape) on the average steady-state flow of foams of various liquid content, and specifically the motion and deformation of their elementary components, the bubbles. In the frame of the flowing foam, we can observe a recirculation around the obstacle, characterized by a multipolar velocity field. Its complex structure displays a strong fore-aft asymmetry, with an extended region downstream the constriction, where the foam velocity can be much larger than the imposed driving one. This overshoot was already revealed for nonpermeable obstacles, but here we show that its extent and intensity are associated to the bubble deformation and depend strongly and nontrivially on both the geometry of the constriction as well as the liquid fraction of the foam.

中文翻译：

---

准二维泡沫流过并围绕可渗透障碍物

我们目前对二维液体泡沫进行实验研究，该泡沫由有限的单层气泡组成，被迫在模拟非均质开放性裂缝的模型多孔介质中流动。它由Hele-Shaw细胞组成，该细胞具有单个局限性收缩样缺陷，可局部缩小其间隙并因此减小其渗透性。利用直接可视化并跟踪气泡的可能性，我们通过对每个气泡拟合椭圆而获得的偏心率测量，通过图像相关分析和气泡变形场来计算气泡速度场。缺陷是渗透障碍会严重干扰泡沫流动；我们在这里研究其几何形状（高度，尺寸和形状）对各种液体含量的泡沫的平均稳态流动的影响，特别是其基本成分气泡的运动和变形。在流动泡沫的框架中，我们可以观察到障碍物周围的再循环，其特征在于多极速度场。它的复杂结构显示出很强的前后不对称性，在缩颈的下游有一个扩展区域，该区域的泡沫速度可能远大于施加的驱动速度。该超调已经显示为不可渗透的障碍物，