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

在自然界和技术中，含有颗粒的流动（悬浮流）存在于无数的环境中;例子包括河流中充满泥沙的水流到通过细胞计数分析仪的血液。众所周知，纯牛顿流体经历导致流动行为显著变化的不稳定性。悬浮液流也经历不稳定性;然而，驱动悬浮液流不稳定性的机制尚未被理解。在这个项目中，证明技术的特点，在纯牛顿流体的不稳定性将适用于悬浮液流的不稳定性。这种方法应该揭示如何探测和操纵这种不稳定性，以开发更好的方法来预测粒子在实际应用中的运动和分布。拟议的项目预计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新研究生和本科生，并以非技术形式向教育系统各级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）流的不稳定性的大量基础和应用知识，以实现对悬浮液流不稳定性的突破性理解。具体来说，该项目将测试主要的牛顿洞察力，即结构化的流动几何形状可以展开过渡过程，以揭示分离良好，非湍流过渡所产生的不稳定性，可以通过施加适当设计的扰动进行操纵。该项目采用新的实验室实验和现有理论来探索结构化渠道中的悬浮液流动。首先，层流稳定状态将被表征为特定颗粒尺寸和选定的平均颗粒体积分数的雷诺数的函数。然后研究纯牛顿流体和悬浮液流动不稳定性。这个项目的成果应该为未来的研究奠定基础，以调查新的和迄今为止未知的基本流体物理学，当惯性粒子被添加到流中。我们的工作成果应该为发现操纵流动和粒子的新方法奠定基础。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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.