Multiple states of bubble propagation in partially occluded tubes.

在这个建议中概述的项目是关于研究在部分闭塞管中两相位移流中的新型分岔现象。一种液体被另一种液体取代是许多应用的基础，从控制微流体装置中的气泡流量到提高石油采收率，并且以前已经在均匀截面的管中进行了研究，例如圆形或多边形。然而，在实际的位移流动中，管的横截面可能被部分阻塞，例如，由于多孔材料中相邻孔隙的连接。初步的实验结果表明，在矩形管中引入一个轴向均匀的障碍物，一旦超过无量纲速度，就会导致最初以中心传播的气泡向管的一侧移动。通过调整几何形状，这种转变可以变得非常突然，导致提取的流体体积变化超过三倍，这在石油开采应用中非常重要，因为连接或不规则形状的孔隙会产生局部收缩区域。我们建议通过绘制动力学来描述这些分岔现象，并通过揭示潜在的流体动力学来理解部分闭塞对长传播气泡的影响。这将通过综合利用实验、气泡形状的静态分析以及可以分析分岔现象的三维数值模拟的综合优势来实现。然后，我们建议将这些发现扩展到短气泡，气泡列和最终微流体水平的液滴，并应用所获得的基本理解，通过使用部分闭塞的管作为被动致动器，在连接处引导气泡列。

The project outlined in this proposal is concerned with the investigation of novel bifurcation phenomena within two-phase displacement flows in partially occluded tubes. The displacement of one liquid by another underpins many applications from the control of bubble traffic in microfluidic devices to enhanced oil recovery and has previously been studied in tubes of uniform cross-section, e.g. circular or polygonal. In practical displacement flows, however, the cross-section of the tube may be partially occluded, e.g. due to the connection of neighbouring pores in porous materials. Preliminary experimental results suggest that the introduction of an axially uniform obstacle into a rectangular tube can cause an initially centred propagating bubble to move to one side of the tube once a dimensionless speed is exceeded. By tuning the geometry, this transition can become very abrupt, leading to more than threefold changes in the volume of fluid extracted, which could be important in oil recovery applications where connecting or irregularly-shaped pores create areas of local constriction. We propose to characterise these bifurcation phenomena by mapping out the dynamics, and to gain an understanding of the effect of partial occlusions on long propagating bubbles, by unravelling the underlying fluid dynamics. This will be achieved by drawing on the combined strengths of experiments, static analysis of bubble shapes far behind the tip, and three-dimensional numerical simulations that can analyse bifurcation phenomena. We then propose to extend the findings to short bubbles, bubble trains and ultimately droplets at the microfluidic level, and to apply the fundamental understanding gained to direct a bubble train at a junction by using partially occluded tubes as passive actuators.