Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session U26: Suspensions: Fluid-Particle Interactions and Confined Flows |
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Chair: Alban Sauret, UC Santa Barbara Room: 234 |
Tuesday, November 22, 2022 8:00AM - 8:13AM |
U26.00001: And yet it clogs: bridging of suspensions in constricted channels Alban Sauret, Nathan Vani, Sacha Escudier From pipes, to highways, to arteries, stopping the flow is always inconvenient and sometimes dangerous. Clogging can occur whenever a suspension, comprised of discrete particles dispersed in a liquid, flows through a confined geometry. It is a major issue in many engineering systems, such as additive manufacturing or bioengineering but also in irrigation systems and waste management in civil engineering. In this study, we consider the clogging by bridging, i.e., through the formation of a stable arch of particles at a constriction that hinders the transport of particles downstream of the clog. We characterize the role of the volume fraction of particles and of the constriction size on the lifetime of 3D-printed millifluidic devices. Our results show that for small enough constriction and for any solid fraction of particles, the clogging of the system appears to be a matter of when rather than of if. We rationalize our results using a stochastic approach that provides guidelines to avoid clogging by bridging in constricted channels. Understanding the mechanisms and conditions of clog formation can lead to new design principles and to improve the reliability of many engineering systems. |
Tuesday, November 22, 2022 8:13AM - 8:26AM |
U26.00002: Discontinuous Clogging of Rigid Particles in Tapered Microchannels Olukayode T Majekodunmi, Sara M Hashmi This study describes the clogging of rigid particles in a microfluidic device made up of parallel microchannels which taper from the inlet to the outlet, where the constriction width is equal to the particle size. The geometry summarizes clogging dynamics in flow channels that narrow over multiple length scales. Flow tests are conducted at constant driving pressures for different particle volume fractions, and a power-law decay peculiar to the tapered geometry of the channels is observed in all cases. Compared to non-tapered channels, the power-law exponent shows the flow decay rate is significantly lower in a tapered channel. Changes in particle volume fraction at a constant driving pressure affect the clogging rate without impacting the underlying dynamics. Also, the post-clogging permeability of the device reveal two distinct driving pressure regimes, though only a small portion of the device volume and channels surface area were occupied by clogs, regardless of the particle volume fraction – which suggests differences in particle packing behavior. |
Tuesday, November 22, 2022 8:26AM - 8:39AM |
U26.00003: Shear-induced diffusion of smooth and roughened particles Jason E Butler, Han Zhang, Phong Pham, Bloen Metzger, Dmitry I Kopelevich The shear-induced diffusivity of non-Brownian and neutrally buoyant spheres suspended in a viscous fluid were measured using a custom-built shear cell. Measurements were performed on monodisperse and relatively smooth spheres, then the measurements were repeated after the spheres were roughened using a mechanical process. Unexpectedly, the roughened spheres were more diffusive than the original, smooth spheres for volume fractions in excess of 0.25. Simulations that balance viscous drag and contact forces on each particle predict two regimes of dependence of the diffusion coefficient on roughness: below a volume fraction of 0.2, rougher particles were found to have a larger diffusivity, but a lower diffusivity at volume fractions higher than 0.25. At low volume fractions, the displacement induced by each collision is larger for higher values of roughness, and hence the diffusivity increases with particle roughness. At high volume fractions, the increased roughness promotes organization of the concentrated particles into layered structures aligned in the flow direction. This organization results in fewer particle collisions and a corresponding decrease in the diffusivity for rougher particles. |
Tuesday, November 22, 2022 8:39AM - 8:52AM |
U26.00004: Magnetic microrollers maneuvering in a structured fluid Shih-Yuan Chen, Michelle R Driscoll Micro swimmers in a fluid can either self-propel or be driven by external forces. The interactions between micro swimmers and their surroundings lead to a wide range of phenomena: self-assembly, phase separation, transportation of cargo, etc. Likewise, studying such interactions helps us to probe local rheology and material parameters such as the effective viscosity of a colloidal solution or the viscoelasticity of a non-Newtonian fluid. In this talk, I will demonstrate how magnetically driven microrollers maneuver in structured environments. When the rollers are spun by an external magnetic field, they pump fluid around themselves, driving them to move in the desired direction. This also generates strong flows that can reconfigure the nearby environment. I will discuss two hydrodynamic phenomena we study in this microroller system. I will show how the microrollers restructure passive colloids to form a new, steady configuration, and argue that the balance between Brownian motion and the flow velocity determines the size of the structure, which is an order of magnitude larger than the roller. We will additionally explore how these microrollers interact with a structured polymeric fluid. |
Tuesday, November 22, 2022 8:52AM - 9:05AM |
U26.00005: Elastohydrodynamic repulsion between particles translating near an elastic sheet Arash Kargar-Estahbanati, Tal Lifshitz, Naomi Oppenheimer, Bhargav Rallabandi The biological world can be extremely soft, and biological membranes are easily deformed by the motion of nearby particles. The motion of a single particle translating near a soft substrate is well-studied in recent years. In this work, we investigate, using theory and experiments, the interaction between two particles sedimenting side-by-side near a soft substrate. Experimentally, we measure the relative displacement of two millimetric-sized spheres settling under gravity alongside an elastic sheet suspended in silicone oil. We observe that the spheres drift apart from each other while deforming the elastic sheet as they settle, whereas no such drift is observed in the absence of the sheet. We rationalize this behavior using numerical solutions of elastohydrodynamic lubrication theory for the two-particle system, and show that the particles drift apart as a result of a symmetry-breaking deformation of the nearby sheet. The hydrodynamic pressure associated with the motion of each particle deforms the sheet, which, in turn, generates a secondary flow that repels the other particle in the direction normal to the direction of settling. We validate the numerical results by developing an analytic theory, based on the Lorentz reciprocal theorem, for small deformations of the sheet. Our analysis shows that this elastohydrodynamic interaction is long-ranged and depends on both the bending rigidity and tension of the sheet. We posit that these elastohydrodynamic interactions are relevant to the motion of suspensions in confined soft systems. |
Tuesday, November 22, 2022 9:05AM - 9:18AM |
U26.00006: Influence of inertia on the rotation of axisymmetric particles in shear flow Davide Di Giusto, Laurence Bergougnoux, Cristian Marchioli, Elisabeth L Guazzelli We experimentally investigate the rotational dynamics of a neutrally-buoyant axisymmetric particle in a viscous shearing flow. A custom-built shearing cell and a multi-view shape reconstruction method are used to obtain direct measurement of the period and the angular phase of the Jeffery orbits (Jeffery, 1922), focusing on oblate and prolate shapes (both ideal objects such as ellipsoids but also objects of practical interest such as cylinders). By systematically changing the viscosity of the fluid, we examine the effect of inertia on the dynamical behaviour of the suspended particle. While the measurements of the period of rotation are in good agreement with the results found in the Stokes regime, we report a systematic drift among several rotations toward limiting orbits for both fibers and disks. This is compared to the most recent small-inertia theories (Einarsson et al., 2015; Dabade et al., 2016). |
Tuesday, November 22, 2022 9:18AM - 9:31AM |
U26.00007: Investigation of hydrodynamic forces on non-spherical particles during rebound on a flat surface Tiffany Simmons, Mohsen Daghooghi, Iman Borazjani A sharp-interface curvilinear immersed boundary (CURVIB) method is used to simulate the fluid-structure interaction for three-dimensional, single, non-spherical particles for a gravity-driven fall and rebound on a flat surface in a viscous fluid. Kinematic equations of motion are implemented to compute the 6 degrees of freedom for the particle's motion before, during, and after the collision. The coefficient of restitution is set from experimental data found in the literature and used in our kinematic-based collision model. Sensitivity studies for the grid, domain, and boundary conditions are performed to ensure the independence of the results from the computational setup, and the code is validated against experimental data for a brick rebounding in air and a sphere in a viscous fluid. Different particle shapes are tested, such as cube, ellipsoid, cylinder, pyramid, and a jagged, irregular shape. How the hydrodynamics forces from the viscous fluid vary for each non-spherical particle during rebound, and their scaling is investigated. |
Tuesday, November 22, 2022 9:31AM - 9:44AM |
U26.00008: Hydrodynamics of a single filament moving in a supported spherical bilayer Wenzheng Shi, Moslem Moradi, Ehssan Nazockdast Dynamic assembly of biopolymers and rod-like proteins on membranes is key to many cellular processes. The protein dynamics is determined, in part, by its membrane-mediated hydrodynamic resistance/mobility. Using a slender-body formulation, we compute the translational resistance of a single rod of length L moving in the outer layer of a bilayer membrane with 2D viscosity η_{m}, supported by a rigid inner sphere of radius R, and surrounded by a Newtonian fluid of viscosity η on the exterior. This geometry models membrane-coated beads that are frequently used in in-vitro studies. The outer- and inner-layer are coupled through a Brinkman-like friction term with a coefficient μ. We find that the dimensionless resistance in the directions parallel to the rod’s axis and perpendicular to it, γ_{‖,⊥}/(4πη_{m}), depends only on the ratio L/L^{†}, where L^{†} is the length scale over which momentum is transferred from the membrane to the exterior fluid and is determined as the minimum of the following three length scales: L^{†}=min(η_{m}/η, R, (η_{m}/μ)^{½}). Furthermore, we study the relaxation spectrum of transverse correlation of a semi-flexible filament on the geometry and find a non-monotonic transition regime between two dynamical regimes of long and short wave-vector around qR~1 (q is wave-vector). This novel behavior arises from flow confinement in spherical geometry and is absent in planar membranes. |
Tuesday, November 22, 2022 9:44AM - 9:57AM |
U26.00009: Settling dynamics of flexible Brownian filaments Lucas Hildebrand Pires da Cunha, Jingjing Zhao, Sibani Lisa Biswal, Frederick C MacKintosh We investigate the settling dynamics of flexible Brownian filaments by analyzing a wide range of Peclet numbers. Using the Brownian Dynamics method, we simulate the dynamics of a single filament over a long period to take statistical measurements of the effective settling velocity and diffusion perpendicular to gravity. We observe that the competition between gravitational and thermal effects can either increase or decrease the settling velocity of the filaments, depending on their flexibility. At highly flexible regimes, we identify gravitational induced compaction of the structure leading to faster sedimentation. Also, the system shows interesting stretching and compacting non-periodic dynamics in which one of the ends is pulled out of and pulled into the compact structure. Contrastingly, for semi-flexible filaments, the compact structures are not observed. Nonetheless, the interplay between elastic, gravitational, and thermal forces leads to important secondary influences on the filament diffusion perpendicular to gravity. |
Tuesday, November 22, 2022 9:57AM - 10:10AM |
U26.00010: Sedimenting flexible fibers against obstacles in a viscous fluid Ursy Makanga, Mohammadreza Sepahi, Camille Duprat, Blaise Delmotte The motion of flexible fibers often happens in complex media that are structured by obstacles. Examples range from the transport of biofilm streamers through porous media to the design of sorting devices for DNA molecules. For large number of such problems, the dynamic of the fibers result from the complex interplay between internal elastic stresses, contact forces and hydrodynamic interactions with the walls and obstacles. By means of numerical simulations, experiments and analytical predictions, we investigate the dynamics of flexible fibers settling in a viscous fluid embedded with obstacles of arbitrary shapes. We identify various regimes on the dynamics of a single fiber, such as prolonged periods of trapping around the obstacle and lateral dispersion. The magnitude of this lateral displacement, in the same order as its length, depends on the fiber characteristics, an effect we leverage on to propose a sensitive sorting solution based on the fiber length and/or mechanical properties. Furthermore, we examine the conditions under which a fiber may remain trapped on the obstacle, and identify non-trivial wrapping configurations, providing design clues for optimal sorting/filtration. |
Tuesday, November 22, 2022 10:10AM - 10:23AM |
U26.00011: Fat content and hematocrit: How do the constituents of milk and blood influence their final deposition patterns? Garam Lee, Jack Verich, Mark Greer, James Bird A sessile droplet containing particulates leaves a ring-like formation when it is dried. Particle size, shape, and volume fraction can affect the final deposition pattern and the crack density by manipulating the contact line dynamics and the internal flow. When there is more than one type of particle suspended in a droplet, the combination results in more complex dynamics and patterns. Here we explore two different biofluids, blood and milk, that can be thought of as a mixture of particulates with different sizes, densities, and stiffness to study how the concentration of different particles affects the final drying pattern. Various types of milk ranging from skim milk to cream diluted in water are used, and the results are compared to blood with different hematocrit, focusing on the ring width and the crack pattern. |
Tuesday, November 22, 2022 10:23AM - 10:36AM |
U26.00012: Coagulation of like-charged Brownian Particles Pijush Patra, Anubhab Roy We study the coagulation rate of Brownian particles dispersed in a gaseous medium. Particles are small enough so that their inertia is negligible. Most previous calculations of the Brownian-induced coagulation rate have considered that the particle pairs interact through continuum hydrodynamics and van der Waals attraction forces at close separations allow the collision and subsequent coagulation. However, the continuum approximation of the hydrodynamic interactions is no longer valid when the gap thickness between the surface is less than the mean-free path of the surrounding fluid medium and the non-continuum lubrication interactions lead to surface-to-surface contact in finite time. The Knudsen number, defined as the ratio of the mean-free path to the medium to the average radius of the interacting particles, measures the effects of non-continuum interactions. We calculate the Brownian-coagulation rate in the presence of non-continuum lubrication resistances. We also report the effect of van der Waals and electrostatic forces on the coagulation rate while particles interact with each other through non-continuum hydrodynamics. |
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