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 A36: Suspensions: Fluid-Particle Interaction INon-Newtonian Particles
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Chair: Qin M. Qi, Stanford University Room: 302 |
Sunday, November 19, 2017 8:00AM - 8:13AM |
A36.00001: In-vitro measurement and modelling of shear-induced platelet margination and adhesion in channel flows Qin M. Qi, Irene Oglesby, Jonathan Cowman, Antonio J. Ricco, Dermot Kenny, Eric S.G. Shaqfeh Blood coagulation is initiated by GPIb and GPIIbIIIa receptors on the platelet surface binding with von Willebrand factors tethered on the vascular wall. This process occurs much faster in the presence of flow shear than in the quiescent fluid. First of all, the near-wall platelet concentration in flowing blood increases significantly. This phenomenon, commonly referred to as platelet margination, is due to shear-induced hydrodynamic interactions between red blood cells and platelets. Flow shear also manifests itself in affecting the reaction kinetics of receptor-ligand binding. The breaking and formation of multiple bonds on the platelet surface result in the translocating motion of platelets rolling close to the vascular wall. To date, a fundamental understanding of how fluid mechanics relate the bond-level kinetics to the platelet-level dynamics is very limited. In this talk, we investigate platelet adhesion under physiological shear rates using both microfluidic experiments and multi-scale modeling. Our model, (based on existing single molecule measurements and hydrodynamics of blood at zero Reynolds number) shows good agreement with experimental results. We discuss the roles of red blood cell volume fraction (hematocrit), shear rate, receptor densities in the dynamics of platelet adhesion. These findings also provide implications for how platelet defects and abnormal flow conditions influence hemostasis and thrombosis. [Preview Abstract] |
Sunday, November 19, 2017 8:13AM - 8:26AM |
A36.00002: The motion of a cloud of solid spherical particles falling in a cellular flow field at low Stokes number Benjamin Marchetti, Laurence Bergougnoux, Elisabeth Guazzelli We present a jointed experimental and numerical study examining the influence of vortical structures on the settling of a cloud of solid spherical particles under the action of gravity at low Stokes numbers. The two-dimensional model experiment uses electro-convection to generate a two-dimensional array of controlled vortices which mimics a simplified vortical flow. Particle image-velocimetry and tracking are used to examine the motion of the cloud within this vortical flow. The cloud motion is compared to the predictions of a two-way-coupling numerical simulation. [Preview Abstract] |
Sunday, November 19, 2017 8:26AM - 8:39AM |
A36.00003: Shear induced migration of particles in a yield stress fluid: experiment Sarah Hormozi, Mohammad Gholami, Ahmadreza Rashedi, Nicolas Lenoir, Guillaume Ovarlez We have performed rheometry coupled with X-ray radiography in a narrow gap Couette cell filled with a suspension of spherical particles in a yield stress fluid. In this setup, the shear rate is discontinuous changing from a constant value in the gap to zero in the reservoir located at the top. This shear rate inhomogeneity results in the migration of particles from the gap to the reservoir, so-called Shear Induced Migration (SIM). The rheometry results give us insight into understanding the bulk rheology in the presence of shear rate and solid volume fraction inhomogeneities. In addition to that, our recent X-ray radiography technique (Gholami et al, JOR. 2017) provides detailed information about the evolution of the solid volume fraction in the domain. These measurements allow us to refine the recent continuum model frameworks (Hormozi & Frigaard, JFM 2017) for SIM of particles in a yield stress suspending fluid. We show that complex rheology of the yield stress suspending fluid and formation of the islands of unyielded regions in the reservoir strongly affects the SIM of particles. This feature is absent when we deal with a Newtonian suspending fluid. [Preview Abstract] |
Sunday, November 19, 2017 8:39AM - 8:52AM |
A36.00004: The interaction of two spheres in a simple-shear flow of complex fluids. Mohammadhossein Firouznia, Bloen Metzger, Guillaume Ovarlez, Sarah Hormozi We study the interaction of two small freely-moving spheres in a linear flow field of Newtonian, shear thinning and yield stress fluids. We perform a series of experiments over a range of shear rates as well as different shear histories using an original apparatus and with the aid of conventional rheometry, Particle Image Velocimetry and Particle Tracking Velocimetry. Showing that the non-Newtonian nature of the suspending fluid strongly affects the shape of particle trajectories and the irreversibility. An important point is that non-Newtonian effects can be varied and unusual. Depending on the shear rate, nonideal shear thinning and yield stress suspending fluids might show elasticity that needs to be taken into account. The flow field around one particle is studied in different fluids when subjected to shear. Then using these results to explain the two particle~interactions in a simple-shear flow we show how particle-particle contact and non-Newtonian behaviors result in relative trajectories with fore-aft asymmetry. Well-resolved velocity and stress fields around the particles are presented here. Finally, we discuss how the relative particle trajectories may affect the microstructure of complex suspensions and consequently the bulk rheology. [Preview Abstract] |
Sunday, November 19, 2017 8:52AM - 9:05AM |
A36.00005: Sphere interaction in bounded shear flow of Oldroyd-B fluids Shang-Huan Chiu, Tsorng-Whay Pan, Roland Glowinski It is well-known that, up to the initial sphere displacement, binary encounters of spheres in bounded shear flow of a Newtonian fluid can have either swapping or non-swapping trajectories under creeping flow conditions (Zurita-gotor et al., J. Fluid Mech. 592 (2007) 447-469). The motion of dilute sphere suspensions in bounded shear flow of Oldroyd-B fluids at zero Reynolds number has been studied. The pass and return trajectories of the two ball mass centers in a two wall driven shear flow are similar to those in a Newtonian fluid; but they lose the symmetry due to the effect of elastic force arising from viscoelastic fluids. A tumbling chain of two balls (a dipole) may occur, depending on the value of the Weissenberg number and the initial vertical displacement of the ball mass center to the middle plane between two walls. The two ball tumbling motion has also been compared with that of an ellipsoid in bounded shear flow Oldroyd-B fluids. [Preview Abstract] |
Sunday, November 19, 2017 9:05AM - 9:18AM |
A36.00006: Local Lubrication Model for Spherical Particles within an Incompressible Navier-Stokes Flow Baptiste Lambert, Michel Bergmann, Lisl Weynans In particle laden flow, hydrodynamic effects due to close interacting particles play an essential role in the suspension phenomenon. For Stokes flow, the lubrication theory indicates that the dominant order of the lubrication between two spherical particles evolves as a function of the inverse of the separation distance. The divergent behaviour of the lubrication force challenges the accuracy of numerical simulations when the particles are almost in contact. Lubrication is classically modelled using the dominant order of the force given by the lubrication theory. However, these results are rigorously valid only for Stokes flows and spherical particles. We aim at extending the lubrication theory to inertial fluids and more complex particle geometries. We are proposing a subgrid lubrication model for Navier-Stokes flows of particles. In our approach, corrections of the lubrication are made locally at the particle surfaces when there is not enough grid cells between interacting particles to properly compute the hydrodynamic effects. Hence the validity of the correction depends only on the particle curvature and the flow properties near the contact point. Thereby, the method can be generalized any particles with a convex surface, for instance. [Preview Abstract] |
Sunday, November 19, 2017 9:18AM - 9:31AM |
A36.00007: Computing fluid-particle interaction forces for nano-suspension droplet spreading: molecular dynamics simulations Weizhou Zhou, Baiou Shi, Edmund Webb Recently, there are many experimental and theoretical studies to understand and control the dynamic spreading of nano-suspension droplets on solid surfaces. However, fundamental understanding of driving forces dictating the kinetics of nano-suspension wetting and spreading, especially capillary forces that manifest during the process, is lacking. Here, we present results from atomic scale simulations that were used to compute forces between suspended particles and advancing liquid fronts.~ The role of nano-particle size, particle loading, and interaction strength on forces computed from simulations will be discussed. Results demonstrate that increasing the particle size dramatically changes observed wetting behavior from depinning to pinning.~ From simulations on varying particle size, a relationship between computed forces and particle size is advanced and compared to existing expressions in the literature. High particle loading significantly slowed spreading kinetics, by introducing tortuous transport paths for liquid delivery to the advancing contact line. Lastly, we show how weakening the interaction between the particle and the underlying substrate can change a system from exhibiting pinning behavior to de-pinning. [Preview Abstract] |
Sunday, November 19, 2017 9:31AM - 9:44AM |
A36.00008: 3-D conditional hyperbolic method of moments for high-fidelity Euler--Euler simulations of particle-laden flows Ravi Patel, Bo Kong, Jesse Capecelatro, Rodney Fox, Olivier Desjardins Particle-laden turbulent flows are important features of many environmental and industrial processes. Euler--Euler (EE) simulations of these flows are more computationally efficient than Euler--Lagrange (EL) simulations. However, traditional EE methods, such as the two-fluid model, cannot faithfully capture dilute regions of flow with finite Stokes number particles. For this purpose, the multi-valued nature of the particle velocity field must be treated with a polykinetic description. Various quadrature-based moment methods (QBMM) can be used to approximate the full kinetic description by solving for a set of moments of the particle velocity distribution function (VDF) and providing closures for the higher-order moments. Early QBMM fail to maintain the strict hyperbolicity of the kinetic equations, producing unphysical delta shocks (i.e., mass accumulation at a point). In previous work, a 2-D conditional hyperbolic quadrature method of moments (CHyQMOM) was proposed as a fourth-order QBMM closure that maintains strict hyperbolicity. Here, we present the 3-D extension of CHyQMOM. We compare results from CHyQMOM to other QBMM and EL in the context of particle trajectory crossing, cluster-induced turbulence, and particle-laden channel flow. [Preview Abstract] |
Sunday, November 19, 2017 9:44AM - 9:57AM |
A36.00009: Floquet Stability of Tank-treading and Tumbling Capsules in Viscous Shear Flow Spencer Bryngelson, Jonathan Freund Elastic capsules in homogeneous viscous shear flow are observed to display different kinematic behavior, depending on the shear rate, membrane material properties, and resting capsule shape. The stability of their motion has been mapped out, at least in part, via empirical observations of simulations; we build upon this approach with a direct stability formulation and analysis that includes a complete description of the flow-coupled elastic capsule. In our formulation, a linear system is constructed from a boundary integral description via an approach that depends upon the orthogonal basis functions used to represent the capsule geometry. Floquet multipliers are computed to classify the stability of the kinematics. These quantify how viscous dissipation rapidly damps most disturbances. However, we also identify disturbances that decay slowly, over many periods of the capsule motion. We extend our analysis to accommodate an oscillatory extensional flow configuration, which includes transient and time-global instabilities. [Preview Abstract] |
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