Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session E35: Suspensions III: Confined Flows |
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Chair: Jeffrey F. Morris, City College of New York Room: 406 |
Sunday, November 24, 2013 4:45PM - 4:58PM |
E35.00001: Shear stress developed on concentrated suspensions of large particles in turbulent shear flow Esperanza Linares Guerrero, Melany Hunt Experiments were performed on concentrated suspensions of relatively large (mm size) non-spherical particles in an aqueous glycerine mixture. The suspension was sheared using the same coaxial-cylinder rheometer used by Koos {\emph{et al.}}(2012) in which the outer cylinder rotated while the inner one was fixed. The rheometer walls were roughened to avoid slip. Torque measurements for pure fluid and no particles were performed to check for the presence of turbulence. For low Reynolds number ($0.3-3\times10^3$), the torque measurements compare favorably with the theoretical results for Couette flow but for higher Reynolds ($4\times10^3-1\times10^5$), the torques measured are higher than the ones predicted for a laminar flow. Torque measurements of suspensions of varying concentrations of polystyrene particles were performed. Neutrally and non-neutrally buoyant configurations were studied. To account for particle migration and obtain the local solid fraction, visualization of the flow at the inner wall was performed. Results of the effect of particles in a turbulent shear flow will be presented where focus will be given to distinguish whether the flow is dominated by particle interactions or hydrodynamic forces and the influence that the solid fraction has on these mechanisms. [Preview Abstract] |
Sunday, November 24, 2013 4:58PM - 5:11PM |
E35.00002: Modeling the Behavior of Confined Colloidal Particles Under Shear Flow Frances Mackay, Colin Denniston, Mikko Karttunen Numerically, we investigate the behavior of systems of colloidal particles confined between two parallel walls under steady shear flow. We model these particles using molecular dynamics techniques, with hydrodynamic interactions implemented through the use of a lattice-Boltzmann fluid. Starting from an initially ordered particle arrangement, the system evolves into a variety of configurations depending on the volume fraction and shear rate used. The particles either reorder into hexagonally ordered layers aligned along the flow, form purely disordered layers, or separate into higher volume fraction, ordered layers near the walls, and lower volume fraction, disordered middle layers. We present results in the form of a phase diagram, showing the per-layer behavior as a function of volume fraction and shear rate. In addition, by tracking the positions of individual particles we show that the onset and persistence of disorder in these systems is characterized by an exchange of particles between adjacent layers. [Preview Abstract] |
Sunday, November 24, 2013 5:11PM - 5:24PM |
E35.00003: Suspension microstructure in a microporous flow Tharanga Perera, James Gilchrist Suspension flows in porous networks are common in applications such as filtration, oil and extraction processes and in biological systems. Knowing the microstructure in such systems can shed light to the understanding of the underlying physical mechanisms as well as the rheological behavior in such flows. An experimental technique based on Confocal laser scanning microscopy was utilized to determine the microstructure of near-hard-sphere microparticle suspensions based on experimentally obtained 3D particle positions. Previous investigations on suspension structure show results of simulation-like quality produced by this technique. This work outlines how the microstructure of a colloidal suspension evolves as it flows around a post in a well-structured micro-porous medium. The formation of strings under shear closer the post as well as ordering due to wall effects are noticed. [Preview Abstract] |
Sunday, November 24, 2013 5:24PM - 5:37PM |
E35.00004: Microfluidic flow-stabilized solids: formation and deformation Carlos Ortiz, Robert Riehn, Karen Daniels The spectrum of non-affine cooperative rearrangements of amorphous materials is central to understand its time-evolution, mechanical properties, and dynamic susceptibility. We report experiments on the structure and elastic properties of a flow-stabilized amorphous solid that is subject to thermal fluctuations. We study flow-stabilized (Pe$\approx$2-20) quasi-2D heaps composed of a bidisperse mixture of sterically-stabilized submicron polystyrene microspheres. Using a microfluidic device, we control the fluid stress applied on the quasi-static heap, allowing us to deform heaps to maximum strains of up to 10\% and track the real-time propagation of the local deformation. We then reverse the applied stress perturbation to reveal the irreversible non-affine response of the heap. We measure the spatial distribution of the non-affine strain field for deformations of varying amplitude. [Preview Abstract] |
Sunday, November 24, 2013 5:37PM - 5:50PM |
E35.00005: Dispersion of Suspensions in Unsteady Microchannel Flows Martin Maxey, Amanda Howard, Lukas WinklerPrins, Anubhuv Tripathi, Kyongmin Yeo We explore the dispersion of non-Brownian (Pe \textgreater \textgreater 1) suspensions in unsteady, low Reynolds number shear flows in a microchannel. Prior experimental work on oscillating Couette flows and Poiseuille flows has shown the importance of strain amplitude in determining the long term distribution of particles across the channel. We will present results from numerical simulations for the early development of these flows and the motion of finite length suspension plugs. The distortion of a plug by the shear flow results in inhomogeneous particle fluxes across the channel. This is largely reversible over the course of a full cycle, giving reversibility in the bulk. Self-diffusion gives irreversibility though at the microscale. As the strain amplitude increases or the initial volume fraction increases irreversibility in the bulk is seen. The dynamics behind these processes and the role of particle pressure will be noted, together with related experimental observations. [Preview Abstract] |
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