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A Numerical Study on Flagellar Swimming in Viscoelastic Fluids Based on Experimental Data

Posted on:2018-07-04Degree:Ph.DType:Dissertation
University:University of California, DavisCandidate:Li, ChuanbinFull Text:PDF
GTID:1477390020455615Subject:Applied Mathematics
Abstract/Summary:
Many important biological functions depend on microorganisms' ability to move in viscoelastic fluids such as mucus and wet soil. The effects of fluid elasticity on motility remain poorly understood, partly because, the swimmer strokes depend on the properties of the fluid medium, which obfuscates the mechanisms responsible for observed behavioral changes. In this study, we use experimental data on the gaits of Chlamydomonas reinhardtii swimming in Newtonian and viscoelastic fluids as inputs to numerical simulations that decouple the swimmer gait and fluid type in order to isolate the effect of fluid elasticity on swimming. To overcome the numerical stiffness arising from the traditional immersed boundary method, we introduce a shape-prescribed method based on the framework of the immersed boundary method. Our method demonstrates significantly higher efficiency as well as the advantage that the swimmer's gait is exactly followed. We deploy this method in our numerical simulations, and find that in viscoelastic fluids, cells employing the Newtonian gait swim faster but generate larger stresses and use more power, and as a result, the viscoelastic gait is more efficient. Furthermore, we show that fundamental principles of swimming based on viscous fluid theory miss important flow dynamics: fluid elasticity provides an elastic memory.;effect which increases both the forward and backward speeds, and (unlike purely viscous fluids) larger fluid stress accumulates around flagella moving tangent to the swimming direction, compared to the normal direction. We then provide an explanation to this observation by examining the structure of the strain rate for the flow around a cylinder dragged in two different directions and analyzing the elastic responses of the fluid to those flow characteristics.
Keywords/Search Tags:Fluid, Swimming, Numerical
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