Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session L25: Suspensions: Rheology I |
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Chair: Parisa Mirbod, University of Illinois at Chicago Room: 251 C |
Monday, November 25, 2024 8:00AM - 8:13AM |
L25.00001: A minimal continuum model of clogging in spatio-temporally varying channels Anushka A Herale, Duncan R Hewitt, Philip Pearce Particle suspensions in confined geometries exhibit rich dynamics, including flowing, jamming, and clogging. It has been observed that jamming and clogging in particular are promoted by variations in channel geometry or fluid material properties - such variations are often present in industrial systems (e.g. local confinements) and biological systems (e.g. stiffening of red blood cells in deoxygenated conditions in sickle cell disease). The aim of this talk is to shed light on the macroscopic dynamics of particulate suspensions in these conditions. To this end, we present a continuum two-phase model of particle suspensions based on granular rheology that accounts for spatio-temporally varying material properties or channel geometries. The model comprises a continuous particle phase which advects with flow and has material properties dependent on the particle volume fraction, and a suspending fluid which flows through the particle phase obeying Darcy’s law. We solve the system using a finite-volume method and simulate the evolution of an initially uniform particle density. We find that varying material properties and varying geometry can induce heterogeneity in particle volume fraction. We are able to show the emergence of high and low particle density regions in volume-driven flows. These results clarify how spatial variation in material and channel properties can contribute to clogging of particle suspensions. |
Monday, November 25, 2024 8:13AM - 8:26AM |
L25.00002: Hydrodynamic Lubrication of Rough Particles Leads to Friction-like Behavior Jake Minten, Bhargav Rallabandi Hydrodynamic interactions between particles in near-contact configurations dominate the rheological behavior of concentrated suspensions. We study these interactions between cylindrical and spherical particles in near contact using lubrication theory, focusing on the effects of surface roughness. Numerical solutions find that unexpectedly large pressures are generated when two rough particles slide past each other, leading to hydrodynamic forces and torques that are much greater than for smooth particles. Notably, we find that roughness leads to a purely hydrodynamic coupling between rotation and translation reminiscent of dry solid friction, a feature that is absent for smooth particles. We gain insight into these features by developing an analytic theory that resolves the flow around roughness asperities. The theory finds that the near-contact approach of asperities leads to singular and highly localized pressure distributions that generate not only forces, but also torques on the particle. The theoretically predicted hydrodynamic forces and torques are in excellent quantitative agreement with numerical solutions. For rough spheres, we show that the hydrodynamic resistance to tangential sliding scales with the inverse of the separation distance, as opposed to scaling logarithmically with distance for smooth spheres. |
Monday, November 25, 2024 8:26AM - 8:39AM |
L25.00003: Orientation dynamics and stress of spheroids in weakly viscoelastic fluids Tanvi Mahendra Apte, Arezoo M Ardekani, Vivek Narsimhan |
Monday, November 25, 2024 8:39AM - 8:52AM |
L25.00004: On the particle pressure and normal stress differences of dense non-Brownian suspensions of frictionless particles in viscous and inertial regimes Sarah Hormozi, Nishanth Murugan, Donald Koch In this work we explore the non-Newtonian rheology of dense non-Brownian frictionless suspensions close to jamming using a Discrete Element Method. With increasing shear rate the rheology of the suspension displays a transition from a viscous scaling of constant viscosity to a Bagnoldian scaling wherein the viscosity scales linearly with the shear-rate. We report on the scalings for the particle pressure, first and second normal stress differences within the suspension in both the viscous and inertial regimes. The results indicate that the macroscopic friction coefficient for the suspension vanishes as we approach jamming. We argue that this phenomenon is linked to the orientation of microstructural elements within the suspension. |
Monday, November 25, 2024 8:52AM - 9:05AM |
L25.00005: Tuning the rheology and microstructure of colloidal gels via electric field Seyed Mohammad Hosseini, Jae Sung Park Colloidal gels are complex soft materials characterized by a disordered network of short-range attractive particles suspended in a fluid. Owing to their widespread applications in industry and nature, the ability to effectively control their properties is crucial. In this study, we use large-scale Stokesian dynamics simulations to investigate the impacts of an electric field on colloidal gels. Similar to electrorheological (ER) fluids, the application of an electric field causes dipolar interactions, resulting in the formation of chain-like structures along the field direction. As opposed to repulsive suspensions, where viscosity increases with the field magnitude (positive ER effect), the viscosity of colloidal gels can be reduced by increasing the field magnitude (negative ER effect) depending on the ratio of electric and attractive forces. Furthermore, we observe the emergence of cluster rotations due to the competition between dipolar and attractive interactions, which also contributes to the decrease in viscosity. A detailed analysis on microstructure will be given to elucidate the viscosity decrease. In addition, the recovery process after the electric field is off will be explored. |
Monday, November 25, 2024 9:05AM - 9:18AM |
L25.00006: Rheology of dilute suspensions of slender rings in presence of frictional contacts Pulkit Jain, Neeraj Borker, Donald Lyle Koch, Sarah Hormozi Suspensions of slender ring-shaped particles have applications in drug delivery, catalysis, optics, and carbon capture. On a fundamental level, slender rings exhibit a large geometrical resistance to the relative rotation of neighboring particles in a shear flow. Therefore, studying the rheology and microstructure of suspensions of ring-shaped particles transforms our understanding of the role of topology on the nonlinear rheology of suspensions. In our initial study, we investigate the rheology of such non-Brownian suspensions in simple shear flow at low particle number densities. Suspension properties are computed by averaging many pairwise interactions that include hydrodynamic interactions (modelled using slender body theory) and particle contacts (modelled as short-range repulsive forces coupled with Coulombic friction). We explore particle friction coefficients ranging from 0 to 1, along with the infinite friction limit. We find that the contact contribution to the shear stress increases with the friction coefficient and is comparable to other stress contributions. Friction changes the microstructure during collisions in a manner that decreases the first normal stress difference and increases the magnitude of the second normal stress difference. Friction enhances the effective diffusivity of particles in the gradient direction and retards the diffusivity in the vorticity direction. |
Monday, November 25, 2024 9:18AM - 9:31AM |
L25.00007: A framework to link the rheology of thermal amorphous materials to molecular-scale physics Mehryar Jannesari Ghomsheh, Donald Lyle Koch, Sarah Hormozi In amorphous materials, the constituent elements or particles are trapped in metastable configurations due to their neighbors. Under small stresses, these configurations deform elastically, but under large stresses, they rearrange plastically. In thermal amorphous materials, the energy barrier to rearrangement is only moderately larger than the thermal energy. Thus, under mechanical loading, yielding is aided by thermal effects. However, the physics of the yielding transition and the role of thermal fluctuations in this dynamical phase transition are not well understood. We propose a classical density functional theory to obtain molecular-level information concerning the many-body potential between a few polymer-grafted nanoparticles with random configurations and show how the free energy of the system changes from one configuration to another. Then, we introduce a thermally activated elastoplastic model that links the free energy landscape to the bulk rheology. We show how thermal fluctuations can alter the yielding point as the elements hop to new configurations in anticipation. Our theoretical results agree with experiments for a model system of polymer-grafted nanoparticles exhibiting rheological characteristics similar to those of soft glassy materials. By allowing for any functional form of the energy landscape, our framework is applicable to all thermal amorphous materials. |
Monday, November 25, 2024 9:31AM - 9:44AM |
L25.00008: Fractional Step Method for Simulations of Dilute Suspensions at Low Reynolds Numbers. Utkarsh Mishra, Iman Borazjani This study investigates a new proposed fractional step method for low Reynolds number flows. Previous attempts to simulate these flows with the typical fractional step method were constrained by a limited allowable time step size, resulting in high computational costs. Our new solution involves introducing a simple Reynolds number scaling in the fractional step method, which eliminates the restriction on time step size without sacrificing the accuracy of the results. We looked at two scenarios, first a simple channel flow case, which is fundamental to many biological applications. Secondly, we look at fluid-structure interaction cases to examine the rheology of neutrally buoyant rigid ellipsoid particles in periodic suspension which is a more complex case, and the Reynolds number approaches zero. With the typical fractional step method for Reynolds number 0.000001, the required time size (dt) was six orders smaller than the newly proposed fractional step method. This method enables us to investigate the effect of the wall on the rheology of dilute suspensions. We found that as we decrease the distance along the transverse direction, the stresslet of the suspension dramatically changes. |
Monday, November 25, 2024 9:44AM - 9:57AM |
L25.00009: Transient rheology of particle-filled polymer solutions Ankush Mukherjee, Arjun Sharma, Donald Lyle Koch The transient rheology of polymeric fluids containing embedded particles plays an important role in many industrial processes such as hydraulic fracturing and the manufacture of consumer products, pharmaceuticals, and flexible electronics. We extend our recently developed finite difference method for solving polymer flow around spheroidal particles in spheroidal coordinates to describe the rheology of dilute particle suspensions in polymer fluids. Through hybrid numerical-analytical approaches, we describe the particle stresslet, particle-induced polymer stress, and the overall ensemble-averaged suspension stress. We apply our method to understand start-up shear, large-amplitude oscillatory shear of suspensions of spherical particles, and transient shear of suspensions of high-aspect-ratio spheroids with various initial particle orientations. To explore the dynamic polymer conformational response when a suspension experiences time varying flow-types, we analyze the transient flow in a filament stretching rheometer in which a suspension is subjected to pre-shear followed by extensional motion. |
Monday, November 25, 2024 9:57AM - 10:10AM |
L25.00010: Critical behavior of the viscous to inertial shear thickening transition in dense non-Brownian suspensions Nishanth Murugan, Donald Lyle Koch, Sarah Hormozi Dense non-Brownian suspensions exhibit a transition with increasing shear rate, wherein their shear viscosity changes from a constant value at low shear rates to a linearly increasing function of the shear rate when particle inertia becomes important. Experiments on the shear rheology of frictionless non-Brownian suspensions have revealed the shear rate for the transition to sensitively depend on the suspension volume fraction. In this work, we use Discrete Element Method (DEM) simulations to show that the transitional shear rate is indeed sensitive to the volume fraction of the suspension and that it goes to zero as we approach the jamming volume fraction of the suspension. We rationalize that the reduction in the transitional shear rate arises from the growing length scale of the microstructure as one approaches the jamming volume fraction. This allows the development of a scaling framework that yields a collapse of the rheological data across a broad range of volume fractions and shear rates. We confirm this physical mechanism by extracting an estimate of the microstructural length scale and showcasing its role in triggering the viscous to inertial transition. |
Monday, November 25, 2024 10:10AM - 10:23AM |
L25.00011: A Novel Brownian Dynamics Simulation Algorithm to Study the Rheological Properties of a Dilute Suspension of Elastic Prolate Spheroidal Particles John K Stark, Lewis E Wedgewood Rheological properties are calculated for a dilute suspension of elastic prolate spheroidal particles utilizing a novel Brownian dynamics simulation algorithm to account for the effects of particle elasticity on both the suspension dynamics and stress. From force and torque balances on the system, diffusion equations are derived for the configurational distribution functions for both the internal configurations and orientations of the particles in the suspension. These equations are in the form of Fokker-Planck equations and can be interpreted as stochastic differential equations, which are then integrated forward in time using an Euler integration scheme. The particle elasticity can be modeled in various ways, including: (1.) adding springs along each principal axis of a particle or (2.) specifying a form of the stress tensor for the stress inside of a particle. It is assumed that a particle remains spheroidal in shape and that the stress inside of a particle is uniform for the duration of a simulation. Simulation results are compared to numerical results presented by H. Brenner (1974) for rigid prolate spheroidal particles. Extension of the algorithm to elastic triaxial ellipsoidal particles is also discussed. |
Monday, November 25, 2024 10:23AM - 10:36AM |
L25.00012: Defining the structure and properties of colloidal rod systems during dynamic phase transitions Shiqin He, Seth Lindberg, Marco Caggioni, Kelly M Schultz Rheological modifiers are added to formulations to tune rheology, enable function and drive phase changes requiring characterization of material structure and properties. We characterize the dynamic evolution of a colloidal rod used for rheological modification using multiple particle tracking microrheology (MPT). MPT measures the Brownian motion of embedded probes to extract rheological properties. This system consists of polyamide (PA), linear alkylbenzene sulfonate (LAS) and non-absorbing polyethylene oxide, which drives gelation by depletion interactions. We characterize the role of the starting microstructure on gelation using time-cure superposition to determine the critical relaxation exponent, n. n indicates the system structure transitions from a tightly to a loosely associated network at the phase transition depending on the PA:LAS. This is due to the initial PA stability, which is verified by zeta potential measurements. We compare the rheology of PA and hydrogenated castor oil, a polydisperse fiber, and find that polydispersity does not change the rheology and structure of the material during a phase transition. This study will inform future product design by providing guidance to reach desired rheological properties while minimizing trial-and-error experiments. |
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