Collaborative Research: EAGER: Unraveling the Nature and Onset of Instabilities in Suspension Flows

含有颗粒的流动(悬浮流)在自然界和技术中的无数环境中都能找到；例子从河流中充满泥沙的水流到血液流经细胞计数分析仪。众所周知，纯牛顿流体会经历导致流动行为显著变化的不稳定性。悬浮流也经历了不稳定性；然而，驱动悬浮流不稳定性的机理尚不清楚。在这个项目中，用于表征纯牛顿流体中不稳定性的成熟技术将被应用于悬浮流不稳定性。这种方法应该揭示如何探测和操纵这种不稳定性，从而开发出更好的方法来预测粒子如何在实际应用中移动和分布。预计拟议项目还将产生重大的教育影响，包括为下一代科学家和工程师提供解决复杂流动问题的培训，吸引和培训来自代表性不足群体的应届毕业生和本科生，并以非技术性形式向各级教育系统的学生和公众传达主要思想。该项目的主要目标是证明可以利用纯(牛顿)流中关于不稳定性的大量基础和应用知识来实现对悬浮流中不稳定性的突破性理解。具体地说，这个项目将检验牛顿的主要观点，即构建流动几何结构可以展开转变过程，揭示由不稳定引起的良好分离的非湍流转变，这些不稳定可以通过施加适当设计的扰动来操纵。该项目利用新的实验室实验和现有的理论来探索结构化渠道中的悬浮流。首先，对于特定的颗粒尺寸和选定的平均颗粒体积分数，层流稳态将被表征为雷诺数的函数。然后，该研究考察了纯牛顿流体和悬浮流的不稳定性。这个项目的结果应该会为未来的研究奠定基础，以便研究在流动中加入惯性粒子时产生的新的、迄今未知的基本流体物理。我们的工作结果应该为发现操纵流量和颗粒的新方法奠定基础。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Flows containing particles (suspension flows) are found in countless settings in nature and in technology; examples range from silt-laden water streaming in a river to blood coursing through a cell-counting analyzer. Pure Newtonian fluids are well-known to undergo instabilities that lead to significant changes in the flow behavior. Suspension flows also experience instabilities; however, the mechanisms that drive suspension flow instabilities are not yet understood. In this project, proven techniques for characterizing instabilities in pure Newtonian fluids will be applied to suspension flows instabilities. This approach should reveal how such instabilities can be probed and manipulated in service of developing better ways to predict how the particles move and are distributed in practical applications. The proposed project is also expected to have significant educational impacts, including providing training on complex flow problem-solving for the next generation of scientists and engineers, attracting and training new graduate and undergraduate students from underrepresented groups and communicating the main ideas in a non-technical form to students at all levels of the educational system and the general public. The primary goal of this project is to demonstrate that the vast fundamental and applied knowledge of instabilities in pure (Newtonian) flows can be harnessed to achieve breakthrough understanding of instabilities in suspension flows. Specifically, this project will test the main Newtonian insight that structuring the flow geometry can unfold the transition process to reveal well-separated, non-turbulent transitions arising from instabilities that can be manipulated by imposing suitably designed perturbations. The project employs new laboratory experiments and existing theory to explore suspension flows in structured channels. First, the laminar steady state will be characterized as a function of Reynolds number for a specified particle size and selected average particle volume fractions. The research then examines both pure Newtonian fluid and suspension flows instabilities. The outcomes of this project should lay the foundations for future studies to investigate new and heretofore uncharted fundamental fluid physics that arises when inertial particles are added to the flow. The results of our work should set the stage for the discovery of new methods to manipulate flow and particles.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.