Collaborative Research: The leaky rake to solid plate transition on flow through biological filtering structures

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Numerous small organisms that swim, fly, smell, or feed in flow rely on branched, bristled and hairy structures that are significant to biological and biomedical applications. The movement and orientation of such bristled layers can change the behavior of the air or water flow through them such that they may act as either solid plates or leaky rakes. Understanding how animals creatively take advantage of this type of flow transition could inform the design of filters and sampling devices. Although such flows have been studied in many systems, predictive mathematical models of the leaky rake to solid plate transition remain unavailable. The goal of this project is to reveal the physical mechanisms behind this transition through mathematical modeling and experimentation. The theoretical models developed could find applications in biomedical problems such as the flow of lymph and blood through porous tissues and vascular protective layers. In terms of education and outreach, students will be trained at the interface of engineering, mathematics, and biology through interdisciplinary courses, field research, and multidisciplinary group meetings. Diverse students will be recruited through the Louis Stokes Alliance for Minority Participation (LSAMP).This research will elucidate the fundamental fluid dynamics of biological and bioinspired filtering arrays operating at the mesoscale, where inertial and viscous forces are nearly balanced. It will also reveal the fundamental physics of particle capture and exchange when advection and diffusion are nearly balanced. Two types of marine invertebrates will be examined: 1) upside-down jellyfish that drive flow through 3D bristled oral arms, and 2) sea fans that are branched into approximately 2D sheets. Modeling the leaky-to-solid transition is challenging due to the need to simultaneously resolve small-scale flow around micron-scale structures and bulk flow around centimeter-scale arrays. New mathematical models, informed by experiments, will be developed to describe the effective porosity of flexible filtering layers. Particle capture rates and concentration profiles around mesoscale filtering arrays will be quantified experimentally in organisms and physical models. Further details of chemical exchange will be resolved numerically using the immersed boundary method. In terms of biology, these organisms represent one of many examples where particle capture and nutrient uptake occur in mesoscale bristled arrays. Revealing how this strategy is advantageous contributes directly to the NSF Rules of Life. In terms of bioinspired design, these systems exhibit inherently multiscale solutions for filtering and exchange that will provide new insights into the bioinspired design of filtering structures.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.