Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session E36: Suspensions: Fluid-Particle Interaction IINon-Newtonian Particles
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Chair: Michael Sprague, National Renewable Energy Laboratory (NREL) Room: 302 |
Sunday, November 19, 2017 4:55PM - 5:08PM |
E36.00001: Formulation and validation of a computational model for a dilute biomass slurry undergoing rotational mixing Michael Sprague, Jonathan Stickel, Hariswaran Sitaraman In this work we focus on development and validation of a computational fluid dynamics model of a dilute biomass slurry, which is a highly viscous particle-laden fluid for which settling effects can dominate. We model the biomass slurry as a generalized Newtonian fluid that includes biomass-concentration-dependent viscosity and solids transport due to settling and shear. We solve the model with the Nek5000 spectral-finite-element code in a simple vane mixer and calculate the torque as a function of various rotation rates. We compare simulation results against those from experiments for a suspension of 5% wt alpha-cellulose in water. Excellent agreement is demonstrated in the well-mixed regime, and the model satisfactorily captures the transition from the well-mixed regime (at higher rotation rates) to the settled regime (at low rotation rates), but is unable to capture the yield-stress behavior evident in experiments as the rotation rate goes to zero. [Preview Abstract] |
Sunday, November 19, 2017 5:08PM - 5:21PM |
E36.00002: Particle migration in granular suspensions: a numerical study of sedimentation processes Davide Monsorno, Miltiadis Papalexandris In granular suspensions, the particle concentration can vary as a result of convective transport or due to particle migration. These suspensions can often be described as two-phase continuum mixtures; in this case, concentration is expressed by the granular volume fraction. Volume-fraction variations due to particle migration can not be neglected in many flows of practical interest, such as sedimentation processes. From a mathematical perspective, particle migration is associated with a velocity field which is not solenoidal; the numerical treatment of this type of flows can be difficult. In the first part of this talk we elaborate on the challenges presented by their numerical modeling. In the second part of the talk we present numerical results for two flow cases where volume-fraction variations are of primary importance. First, we consider the sedimentation of a dense granular bed under water; we discuss the settling process and the terminal profile (hydrostatics). Subsequently we consider the collapse of a sand column submerged under water. Our results show the formation of a static pile and a turbidity current that is developed due to the collapse. [Preview Abstract] |
Sunday, November 19, 2017 5:21PM - 5:34PM |
E36.00003: On the interplay between hydrodynamic and dipolar particle interactions in suspensions Rafael Gabler Gontijo, Francisco Ricardo Cunha The long range nature of particle interactions in the framework of sedimenting suspensions of magnetic particles is discussed. We present new results on the topic, obtained by an in-house code named SIMS. This code solves simultaneously the equations of translational and rotational motion for each magnetic particle in colloidal and non-Brownian suspensions. We use a sophisticated technique of Ewald summations to compute both hydrodynamic and long-range dipolar interactions for force and torque. A brief discussion on the nature of the spatial decays of the sums used to model our multi-body system and the demand for a periodic geometrical representation of the suspension structure is presented. Examples on the calculation of transport properties of colloidal and non-Brownian suspensions of magnetic spheres are presented and validated. Moreover, we discuss how magnetic interactions affects classical transport properties of sedimenting suspensions and also how hydrodynamic interactions modify the micro-structural dynamics of magnetic colloidal suspensions and consenquently the equilibrium magnetization of the so called ferrofluids. The quantitative results are interpreted in terms of the suspension structure evolution in time. [Preview Abstract] |
Sunday, November 19, 2017 5:34PM - 5:47PM |
E36.00004: Spheres settling in an Oldroyd-B fluid Tsorng-Whay Pan, Roland Glowinski In this talk we present a numerical study of the dynamics of balls settling in a vertical channel with a square cross-section filled with an Oldroyd-B fluid. For the case of two balls, two typical kinds of particle dynamics are obtained: (i) periodic interaction between two balls and (ii) the formation of a vertical chain of two balls. For the periodic interaction of two balls occurred at lower values of the elasticity number, two balls draft, kiss and break away periodically and the chain is not formed due to not strong enough elastic force. For slightly higher values of the elasticity number, two balls draft, kiss and break away a couple times first and then form a chain. Such chain finally becomes a vertical one after the oscillation damps out. For higher values of the elasticity number, two balls draft, kiss and form a vertical chain right away. The formation of three ball chain can be obtained at higher values of the elasticity number. [Preview Abstract] |
Sunday, November 19, 2017 5:47PM - 6:00PM |
E36.00005: Particle sedimentation in a sheared viscoelastic fluid William L. Murch, Sreenath Krishnan, Eric S. G. Shaqfeh, Gianluca Iaccarino Particle suspensions are ubiquitous in engineered processes, biological systems, and natural settings. For an engineering application -- whether the intent is to suspend and transport particles (e.g., in hydraulic fracturing fluids) or allow particles to sediment (e.g., in industrial separations processes) -- understanding and prediction of the particle mobility is critical. This task is often made challenging by the complex nature of the fluid phase, for example, due to fluid viscoelasticity. In this talk, we focus on a fully 3D flow problem in a viscoelastic fluid: a settling particle with a shear flow applied in the plane perpendicular to gravity (referred to as orthogonal shear). Previously, it has been shown that an orthogonal shear flow can reduce the settling rate of particles in viscoelastic fluids. Using experiments and numerical simulations across a wide range of sedimentation and shear Weissenberg number, this talk will address the underlying physical mechanism responsible for the additional drag experienced by a rigid sphere settling in a confined viscoelastic fluid with orthogonal shear. We will then explore multiple particle effects, and discuss the implications and extensions of this work for particle suspensions. [Preview Abstract] |
Sunday, November 19, 2017 6:00PM - 6:13PM |
E36.00006: Solid boundaries: a new way to to a pick a length scale at low Reynolds number Blaise Delmotte, Michelle Driscoll, Paul Chaikin, Aleksandar Donev At low Reynolds number, hydrodynamic interactions between suspended particles are long ranged and strongly depend on the presence of nearby boundaries. In particular, collective motion in a suspension can be strongly modified by a nearby wall. Combining experiments, large scale numerical simulations and continuum models, we investigate two surprisingly overlooked examples that illustrate the effect of a wall on collective motion: (1) the fingering instability in suspensions of particles rotating above a floor (microrollers) (2) the lengthscale selection in suspensions of particles sedimenting parallel to a wall. We will show how these two examples unveil a universal mechanism of lengthscale selection by boundaries at low Reynolds number. [Preview Abstract] |
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