Controlling complex fluid displacement flows in confined geometry

在受限几何中，一种流体受另一种流体的运动是自然界中最常见的过程之一。这些有趣的流也有许多工业应用，例如，在能源领域，特别是在石油工业（例如，在石油和天然气勘探，提取和运输），制造（例如，涂层流，共挤出），生物医学应用（例如，消化，清除肺泡中的粘液塞）和食品加工（例如，生物膜去除，加工机械的清洁）。所涉及的流体经常表现出各种有趣的复杂流变特性，如剪切减薄、剪切增厚、粘弹性、粘塑性和触变效应。这些位移流动通常容易受到众所周知的不稳定性的影响，这些不稳定性可能在流体-流体界面上发展，这取决于情况，可能是不希望的，也可能是理想的。这引发了一个重要的研究问题：如何控制和操纵复杂的流体置换流动，例如，通过阻碍/触发界面不稳定性来实现所需的流动模式和行为？与这个问题相关，我们的长期研究目标是制定综合控制策略，以操纵复杂流体的推进和渗透，阻碍/触发相关的不稳定性，诱导/阻止某些模式的形成，并最大化/最小化所产生的混合。这使得人们能够精确地预测和设计相关系统中多流体流动的行为，减少这些流动的不可预测性和不可控性带来的负面影响。在短期内，由于最近一些研究提出了简单（牛顿）流体位移流动的控制策略，我们将通过研究扩展三种复杂（非牛顿）流体位移流动的控制策略：(i)非均匀几何形状的非牛顿流体位移流动；（ii）非牛顿流体置换流动，施加的流量是可变的；（三）非牛顿流体位移以弹性壁几何形式流动。牛顿流体的最新发展表明，我们的研究是完全可行的；同时回顾大多数自然和工业驱替/驱替流体是非牛顿学说的倡导者，它是绝对必要的。我们提出的研究计划将通过研究生和本科生的大力参与，为培养高素质人才做出贡献。我们将通过开发严格的分析模型（例如，润滑型模型），使用实验技术（例如，流动可视化和测量），以及运用先进的计算流体动力学方法（例如，开放源代码的高质量模拟）来研究提出的丰富的研究课题

The movement of one fluid by another fluid in confined geometry is one of the most common processes in Nature. These interesting flows also have many industrial applications, for example, in the field of energy, particularly in the petroleum industry (e.g., in oil and gas exploration, extraction and transportation), manufacturing (e.g., coating flows, co-extrusion), biomedical applications (e.g., digestion, clearing of mucus plugs in alveoli) and food processing (e.g., biofilm removal, cleaning of processing machinery). The fluids involved frequently exhibit various interesting complex rheological features such as shear-thinning, shear-thickening, viscoelastic, viscoplastic and thixotropic effects. These displacement flows are often vulnerable to well-known instabilities that may develop at the fluid-fluid interface, which depending on the situation may be undesirable or desirable. This sparks a significant research question: How can one control and manipulate complex fluid displacement flows, e.g., by hindering/triggering interfacial instabilities to achieve desired flow patterns and behaviours? Relevant to this question, our long-term research goal is to develop comprehensive controlling strategies to manipulate the advancement and penetration of complex fluids into one another, hinder/trigger the associated instabilities, induce/deter certain pattern formations, and maximize/minimize the resulting mixing. This enables one to precisely predict and design behaviours of multi-fluid flows in relevant systems, reducing concomitant negative impacts associated to unpredictability and uncontrollability of these flows. In the short-term, motivated by a number of recent studies that propose controlling strategies for simple (Newtonian) fluid displacement flows, we will extend three controlling strategies for complex (non-Newtonian) fluid displacement flows through studying: (i) Non-Newtonian fluid displacement flows in non-uniform geometry; (ii) Non-Newtonian fluid displacement flows with a variable imposed flow rate; (iii) Non-Newtonian fluid displacement flows in elastic-walled geometry. The recent developments for Newtonian fluids suggest that our research is completely feasible; while recalling that most natural and industrial displacing/displaced fluids are non-Newtonian advocates that it is absolutely necessary. Our proposed research programme will contribute to the training of Highly Qualified Personnel through strongly involving both graduate and undergraduate students. We will investigate the rich research topics proposed through developing rigorous analytical models (e.g., lubrication-type models), using experimental techniques (e.g., flow visualization and measurements), and exercising advanced computational fluid dynamics methods (e.g., high quality simulations by open source codes).**