Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session F37: Non-Newtonian Flows: Rheology |
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Chair: Sara Hormozi, Ohio University Room: Georgia World Congress Center B409 |
Monday, November 19, 2018 8:00AM - 8:13AM |
F37.00001: Uncertainty quantification in passive microrheology Christel Hohenegger, Scott A McKinley Complex fluids have long been characterized by two functions that summarize the fluid’s elastic and viscous properties, the storage and loss moduli. Information about these bulk fluid properties can be inferred from the path statistics of immersed, fluctuating microparticles. In this talk, we describe a systematic study of this multi-step protocol and we analyze errors and uncertainties intrinsic to it. Particle velocities are assumed to be well-described by the Generalized Langevin Equation uniquely characterized by a memory kernel, which is hypothesized to be inherited from the surrounding fluid. We treat the reconstruction of the memory kernel as an inverse problem and apply nonlinear least-square optimization to numerically generated data to obtain parameters for different linear viscoelastic models. We show that, despite the fact that certain parameters are essentially unidentifiable on their own, the protocol is remarkably effective in reconstructing the storage and loss moduli in a range that corresponds to the experimentally observable regime. We also discuss the errors associated with different numerical approximation of the Laplace transform of the mean square displacement. |
Monday, November 19, 2018 8:13AM - 8:26AM |
F37.00002: Interface-resolved simulations of a sphere settling in simple shear flows of elastoviscoplastic fluids Mohammad Sarabian, Marco Edoardo Rosti, Luca Brandt, Sarah Hormozi We present the fluid mechanics of a settling sphere in an elastoviscoplastic (EVP) material with and without a simple cross shear flow. The objective is to understand how elasticity, plasticity and inertia affect the flow features and consequently the drag force on the sphere. The EVP material is modeled with the constitutive law proposed by Saramito. The single and rigid particle is discretized on a moving Lagrangian grid while the flow equations are solved on a fixed Eulerian grid. The solid particle is represented by an Immersed Boundary method (IBM) with a computationally efficient direct forcing method. Our results show that for constant elasticity, the total drag force on the sphere increases with the yield stress of the material. We infer from our fully resolved numerical simulations that the viscous stresses are the dominant cause of the increase in the particle drag force, while the least contribution comes from the form drag. |
Monday, November 19, 2018 8:26AM - 8:39AM |
F37.00003: Karman Vortex Shedding in Non-Newtonian Blood-Mimicking Fluids Shantanu Bailoor, Jung-Hee Seo, Rajat Mittal Bluff body wakes and vortex shedding have been extensively studied for Newtonian fluids, but they remain relatively unexplored for non-Newtonian fluids. The nonlinear behavior of such fluids widens the parameter-space of the problem, making its characterization difficult. Shear-dependent viscosity is perhaps the most widely modeled constitutive nonlinearity with several inelastic, rheological models proposed in literature. The Carreau-Yasuda model has been used increasingly to model the shear-thinning behavior of blood, however, computational work with this model has been largely restricted to creeping and steady flows. To the best of our knowledge, no data exists in literature for transient Carreau-Yasuda flow over cylinders. To bridge this gap, we present simulation results for unsteady, two-dimensional, shear-thinning Carreau flow over a circular cylinder. We fix the characteristic Reynolds number at 100 and quantify the effect of varying rheological model parameters on the time-varying and mean forces on the cylinder and the vortex-shedding frequency. These results also provide benchmarking data for computational models of non-Newtonian flows, especially those relevant to hemodynamics. |
Monday, November 19, 2018 8:39AM - 8:52AM |
F37.00004: Effects of non-Newtonian fluid on trapped vortices at T-junction Junkyu Kim, Hyoungsoo Kim A typical printing solution consists of multi-component materials. Thus, understanding hydrodynamic effect of complex printing solution in a pipe flow is important to design the printing system including a tubing, nozzle tip and channel branch. Particularly, for the multi-nozzle extrusion system, T-junction is a key element to split and control flow rates at each branch. It is recently reported that for Newtonian fluid, vortices are generated and trapped at Re ~ O(100). The recirculating flow is not favorable for multi-outlets because it is unstable and difficult to precisely control mass transport along the channel. In this study, we numerically study the effect of non-Newtonian fluid at the T-junction. We explore how the vortex develops and evolves at the T-junction where different types of non-Newtonian fluids are applied for instance shear-thinning, shear thickening, and viscoelastic fluid. In conclusion, we will provide design criteria for multi-outlet channels to establish the stable flow pattern. |
Monday, November 19, 2018 8:52AM - 9:05AM |
F37.00005: Extensional Dynamics of viscoplastic and shear thinning liquid bridges John Tsamopoulos, George Makrigiorgos, Yiannis Dimakopoulos The elongational rheology of fluids with yield stress has not been examined as thoroughly as their shear rheology, hence there are many open questions. We study the extension of a liquid bridge confined by two coaxial disks. The material follows the Herschel-Bulkley model and yields according to the von Mises criterion. The upper disk is pulled upwards and the evolution of the bridge shape, particularly its minimum radius, velocity and stress fields are monitored. Assuming axial symmetry, our newly developed Penalized Augmented Lagrangian method (Dimakopoulos et al. JNNFM, 2018) is used to solve the governing equations in 2D. The code is validated by comparing its predictions to experiments by Balmforth et al. (JNNFM, 2010) and finding very good agreement. We examine the effect of the Bingham number (ratio of yield stress to capillary forces), shear thinning, stretching velocity and initial aspect ratio of the bridge and compare our predictions with those by the same authors, who used the 1D slender filament approximation. As these parameters increase, deviation between the approximate results and our computations is observed, owing to the increasing complexity of the yielded domains inside the bridge. |
Monday, November 19, 2018 9:05AM - 9:18AM |
F37.00006: A Theoretical Model for Polyelectrolyte Solutions with Salt Effect Guang Chen, Antonio Perazzo, Howard A Stone Polyelectrolyte (PE) solutions are endowed with both viscous and elastic properties that differ significantly from uncharged polymer solutions. Scaling laws for predicting their viscosity and relaxation time are often based on specific assumptions such as the presence of a theta-solvent, so that the results sometimes fail to explain the conformation or viscoelastic behavior of PE solutions in certain concentration regimes. Here, we use the self-consistent mean-field theory and study the conformation, viscosity and relaxation time of semi-dilute polyelectrolyte solutions in good solvents. We develop a general model that fits well with experimental results and includes excluded volume and counterion screening effects as a function of salt concentration. |
Monday, November 19, 2018 9:18AM - 9:31AM |
F37.00007: Predicting shear rheology of soft interfaces Aditya Raghunandan, Patrick Underhill, Juan Lopez, Amir Hirsa Predicting non-Newtonian shear rheology of soft matter systems at fluid-fluid interfaces has been compromised by using linear (Newtonian) constitutive equations to determine rheological properties. Predicting this nonlinear behavior is integral to the development of engineered products and explaining many biophysical processes. Here, we model the interfacial viscosity as a generalized function of the imposed shear rate and present a non-Newtonian constitutive equation for interfaces under steady shear. We also introduce non-Newtonian material properties that control nonlinear and linear shear responses of an interfacial system. Combining flow field predictions from the new equation and experiments in a knife-edge flow geometry, we demonstrate that monolayers of DPPC – the primary constituent of mammalian cell walls and pulmonary surfactant – are shear-thinning at near-physiological surface packing over six decades of shear-rate. |
Monday, November 19, 2018 9:31AM - 9:44AM |
F37.00008: Chaotic Orbits of Tumbling Ellipsoids in Viscous and Inviscid Fluids Erich Essmann, Pei Shui, Prashant Valluri, Stéphane Popinet, Rama Govindarajan Aref(1993) showed that the dynamics of an immersed tri-axial ellipsoid should be chaotic under certain inviscid conditions. We use analytical and numerical methods to determine occurrence and conditions of chaotic orbits in viscous and inviscid environments. Our numerical work uses Gerris(Popinet et al, 2003) augmented with a fully-coupled solver for fluid-solid interaction with 6 degrees-of-freedom (6DOF). Its adaptive Cartesian mesh scores over traditional algorithms in convergence and also require fewer mesh adaption steps whilst using the immersed boundary method. For inviscid conditions, our numerical results agree with the solution of Kirchhoff’s equations. Our results show that chaos is a strong function of density ratio and the initial energy ratio even for inviscid environments. Using recurrence quantification (Marwanet al, 2007) methods, we also characterise chaos and identify regime shifts from being periodic to quasi-periodic to chaotic. In viscous systems, we have also noted evidence of chaotic orbits for symmetric ellipsoids. We will discuss vortex shedding behaviour in this context. |
Monday, November 19, 2018 9:44AM - 9:57AM |
F37.00009: Sedimentation of particles with nonuniform density at low Reynolds number Xiaolei Ma, Justin Burton Particle sedimentation plays a key role in the accumulation of geological deposits and is essential to many industrial processes. It may also provide a novel route towards self-assembly of particulate films if long-wavelength density fluctuations are suppressed. Recent theoretical predictions suggest that non-spherical objects with nonuniform density can accomplish this task [1]. Here we report experiments focusing on the settling dynamics of such particles at low-Reynolds numbers (∼10^{-3}). Our particles are composed of aluminum and steel spheres glued together in various configurations. A single doublet made of equal-sized aluminum and steel (EAS) balls aligns with gravity, contrary to a doublet made of two aluminum balls, which aligns with fluid flow. For two identical EAS particles, an effective repulsive force is observed during settling due to the competing tendencies to align to the fluid flow and gravity. For three or more pairs of EAS particles, more complex dynamics are observed that are likely due to the chaotic nature of many-body hydrodynamics, yet repulsion between the particles seems to play a key role. Preliminary experiments geared toward realizing hyperuniform structures from sedimentation will also be discussed. [1] Goldfriend, et al., PRL, 118, 158005 (2017) |
Monday, November 19, 2018 9:57AM - 10:10AM |
F37.00010: Lattice-Boltzmann based simulations of ThFFF for separation of colloids and cells Jarrett Valenti, Jessica Jensen, Jennifer Kreft Pearce We present the results of a series of Lattice-Boltzmann based Brownian Dynamics simulations of thermal flow field fractionation for the separation of particles within a fluid. A temperature gradient created in a dilute polymer solution allows us to separate particles based on their deformability. As shown in previous experiments, the level of deformability of a simulated particle changes how the particle moves within the fluid matrix. We thus conclude, that under the correct circumstances, particles of differing deformability can be separated by the fluid alone. Our simulation was intended to model an oceanic system comprised of three different particles: zooplankton, phytoplankton, and microplastics. The data we collected in our simulations suggest the separation of microplastics from plankton is likely. |
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