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

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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.