Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session K13: Non-Newtonian Flows: Polymer Solutions (8:45am - 9:30am CST)Interactive On Demand
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K13.00001: Numerical simulation of unsteady two-dimensional Giesekus flow over a circular cylinder Sai Peng, Peng Yu This study numerically examines vortex shedding of two-dimensional viscoelastic flow over a circular cylinder at a Reynolds number of 100. The Giesekus model is selected to describe the viscoelastic constitutive relationship. The effects of shear-thinning and elastic properties of fluid are discussed. The shear-thinning may trigger the inertial instability by decreasing the apparent viscosity near the cylindrical wall. The elasticity may introduce extensional viscosity in the wake field to suppress flow instability. Macroscopically, the recirculation of the wake field is elongated, and both $C_{lrms} $ and $St$ decrease; and these trends are opposite to those induced by the shear-thinning property. However, our simulations also indicate that strong elasticity may trigger the elastic instability, which is unlike the inertial instability caused by the shear-thinning. Due to the elastic instability, very high flow field fluctuation appears at the leading edge of the cylinder. Additionally, weak elasticity can increase the drag-reduction effect of the shear-thinning solutions. However, strong elasticity or strong shear-thinning may increase the drag. [Preview Abstract] |
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K13.00002: Near-surface dynamics of semidilute polymer solutions: diffusion, nonlinear rheology, and the hydrodynamic boundary condition Gabriel Guyard, Alexandre Vilquin, Fr\'ed\'eric Restagno, Joshua McGraw The near-surface dynamics of polymer solutions challenge both experimental and theoretical efforts, especially in the case of semi-dilute solutions for which chains overlap, yet evanescent wave microscopy allows for the characterization of such interfacial flows. Here we report molecular-size-resolution particle motions in microfluidic channels for pressure-driven flows of semidilute polymer solutions. The results using polymer-free water are in good agreement with Stokes-flow hydrodynamic and diffusive theory. Experiments using polyacrylamide at different volume fractions close to and above the overlap concentration are done in the same chips as for the water experiments. In contrast to Newtonian fluid behaviour, the shear-rate/pressure drop relation is non-linear for the polymer solution flows, suggesting nanometrically resolved, and shear-thinning effects, accompanied with a non-trivial hydrodynamic boundary condition. The diffusive motion of the tracer particles is also distinguished from that of the water experiments, and such motions detailed here. These results set the basis for a study of near-wall hydrodynamic flow and diffusion in complex fluids, notably including semidilute polymer solutions. [Preview Abstract] |
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K13.00003: Viscous and viscoelastic fingering Fahed Albreiki, Alexander Kubinski, Prerana Rathore, Andrew Rasmussen, Vivek Sharma The displacement of more viscous fluid by a lower viscosity fluid in quasi two dimensional flow created in so called Hele Shaw cell is observed to create complex fingering patterns. The viscosity ratio of inner and outer fluid is known to influence the shape and shape evolution of fingers in the case when both fluids are Newtonian. In this contribution, we examine the influence of viscoelasticity on onset and evolution of fingering instabilities, by utilizing model viscoelastic fluids with rate-independent shear viscosity. The analysis of viscoelastic fingering is complemented by a careful evaluation of shear and extensional viscosity as well as Normal stress differences, and their role in determining the outcomes for interfacial~instabilities. [Preview Abstract] |
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K13.00004: Macromolecular engineering of pinching dynamics, extensional rheology and processability Vivek Sharma, Jelena Dinic, Leidy Jimenez, Carina Martinez We elucidate the influence of chemical structure on macromolecular hydrodynamics, rheological response, and drop formation/liquid transfer. We contrasting the shear and extensional rheology response of aqueous solutions of semi-flexible 2-hydroxyethyl cellulose (HEC) with solutions of flexible, polyethylene oxide (PEO). We critically analyze the radius evolution data obtained using Dripping-onto-Substrate (DoS) rheometry to argue that the solutions of flexible PEO macromolecules exhibit signatures of underlying coil-stretch transition not observed for the solutions of semi-flexible HEC. We distill out how length, diameter and number of Kuhn segments affects macromolecular dynamics, rheological response and processability, and infer that the ratio of packing length to Kuhn length, a parameter we term as segmental dissymmetry, helps to hone in on the contrast related to flexibility and extensibility, that are determined by chemical structure for macromolecules comparable molecular weight. [Preview Abstract] |
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