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 L36: Particle-Laden Flows: Non-Spherical and Deformable Particles I |
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Chair: Paul Millett, University of Arkansas Room: 244 |
Monday, November 21, 2022 8:00AM - 8:13AM |
L36.00001: Three-dimensional dynamics of elastica in a shear flow Maria Ekiel-Jezewska, Pawel Sznajder, Lujia Liu, Piotr Zdybel, Maria Ekiel-Jezewska We analyze three-dimensional dynamics of an elastic filament in a shear flow of a viscous fluid at low Reynolds number and high Peclet number. We solve the eigenproblem for the Euler-Bernoulli beam (elastica) model by the Chebyshev spectral collocation method. We reduce it to a description in terms of a single parameter X, dependent on the filament flexibility (relative to the shear rate) and its orientation. In this way we show that the solution is the same as in case of the two-dimensional elastica dynamics in shear flow [Becker and Shelley, Phys. Rev. Lett. 2001], and the three-dimensional elastica dynamics in the compressional flow [Chakrabarti et al., Nature Physics, 2020]. We analyze the odd and even eigenfunctions, and provide their simple analytic approximation, dependent on two parameters, m and the wave number k, that scale as the square root of X. The spectrum is shown to be linear in X. These scalings, together with other properties, are reproduced by the results of our numerical simulations for elastic fibers of a non-zero thickness, made of beads interacting hydrodynamically with each other. The numerical simulations are performed by the precise Hydromultipole numerical codes, based on the multipole expansion of the Stokes equations, corrected for lubrication. |
Monday, November 21, 2022 8:13AM - 8:26AM |
L36.00002: Computer Simulations of Elastic Capsule Suspension Flow within Rectangular Microfluidic Channels Paul C Millett Three-dimensional simulations were performed to study the pressure-driven flow dynamics of elastic capsule suspensions within rectangular cross-section channels. The simulations utilize the Lattice-Boltzmann method to model the fluid, as well as an Immersed Boundary method to integrate the elastic forces resulting from the capsule membrane deformation. The capsule volume fraction is held at 10% (i.e., a semi-dilute suspension), while several parameters are systematically varied including the channel Reynolds number (Re), the capillary number (Ca, defining the elasticity of the capsule membranes), and the cross-sectional channel dimensions. Depending on the channel dimensions, each simulation contains between several dozen to several hundred capsules. Flow-induced capsule deformation results from both capsule-fluid interactions (in particular the local shear rate) as well as capsule-capsule interactions. For relatively soft capsules, inertial focusing is observed for Re > 100 characterized by a narrowing of the capsule distribution towards the channel centerline as well as an increase in the cell-free layer adjacent to the channel walls. The degree of inertial focusing is also found to depend on the channel dimensions relative to the capsule diameter. The relative viscosity of the suspension (relative to the capsule-free fluid) and the principal tension within capsule membranes is analyzed within the parameter space described above. |
Monday, November 21, 2022 8:26AM - 8:39AM |
L36.00003: Deformation and fragmentation behaviors of phytoplankton and plastic particle aggregates Yixuan Song, Matthew J Rau, Adrian Burd The formation and disruption of aggregates in natural and synthetic aqueous environments depend heavily on both the interfacial conditions of the particles and the hydrodynamic forces they are exposed to. The interfacial conditions relevant to the aggregation of plastic particles are relatively well understood but knowledge of the bonding properties of aggregates formed from biological aquatic particles is still limited. To better understand the biological bonding forces, we implemented aggregate breakup experiments using both phytoplankton and plastic particles. In this study, we cultured two species of diatom phytoplankton and made simulated marine aggregates in the laboratory using a cylindrical roller tank filled with seawater. We also prepared polyethylene and polystyrene aggregates using different aqueous salt solutions but in the same facility. The size of the formed aggregates ranged from hundreds of microns to a few millimeters for all particle types. To deform and disrupt the aggregates with calibrated hydrodynamic shear, we superimposed a harmonic oscillation to the rolling motion of the tank, which created a laminar oscillating boundary layer near the tank wall. Using high speed imaging and a particle tracking and breakup detection algorithm, we performed dynamic and morphological analyses of individual fragmentation events as well as population-level statistical analyses to compare the behavior of the different particle types. Here, we summarize the deformation and breakup behavior and compare the breakup strength of the four different types of aggregates investigated. We find that polystyrene aggregates were weaker than the phytoplankton aggregates but that polyethylene aggregates were too strong to be disrupted in shear relevant to the ocean. The bounds of two plastic particle aggregates provide us with more insights into the strength of phytoplankton aggregates. |
Monday, November 21, 2022 8:39AM - 8:52AM Author not Attending |
L36.00004: A 3D numerical membrane model for simulating red blood cells (RBC) dynamics and transport Anirudh Asuri Mukundan, Antoine G Morente, Aashish Goyal, Anthony Wachs The predominant components of human blood are red blood cells (RBC) and the plasma fluid. The RBC membrane exhibit non-Newtonian behavior commonly modeled using dissipative particle dynamics (DPD) approach (Pivkin and Karniadakis PRL 2008) and Finite Element approach (Balogh and Bagchi JCP 2017) while the plasma (outside RBC) and cytoplasm (inside RBC) exhibit Newtonian behavior modeled using Finite Volume technique. A physically realistic membrane model coupled with a fast accurate fluid solver is required for simulating RBC dynamics. |
Monday, November 21, 2022 8:52AM - 9:05AM |
L36.00005: Hydrodynamic Force Coefficients for Spherical Shell Fragments: Dependence on the Aspect-Ratio and Flatness Ian G Adams, Julian Simeonov, Carley Walker Euler-Lagrange simulations of particle-laden flow require hydrodynamic models of drag and lift forces on individual particles. Currently there are no universal models that can prescribe these forces for both irregularly shaped and arbitrary orientated particles. Here, we use OpenFOAM RANS simulations of steady bottom-boundary layer flow of Reynolds number 12,000 over a series of irregularly shaped spherical shell fragments. These fragments cover a range of elongation and flatness characteristics. This work is an extension of previous modeling efforts to create a predictive hydrodynamic force model for arbitrary rotations of an intact shell. Here, shell fragments are generated as triangular selections of a spherical shell with azimuthal and longitudinal angles proscribed based on elongation and flatness parameters (varying between 1 to 5, and 0.02 to 0.2 respectively), while the fragment surface area is held constant to define the overall fragment size. The simulations explicitly resolve the wall boundary layers using O(y+=1) grid spacing at the shell fragment surface and use the SST k-omega turbulence closure model. Fragment orientations are considered with independently varying pitch, roll, and yaw each ranging from 0 to 180 degrees. The numerical estimates for the forces from all simulations were used to develop robust parameterizations of the drag and lift as a function of aspect ratio and flatness characteristics, as well as orientation of the shell fragments. |
Monday, November 21, 2022 9:05AM - 9:18AM |
L36.00006: Experimental measurement of spinning rates of Kolmogorov scale slender fibres Vlad Giurgiu, Giuseppe Caridi, Mobin Alipour, Marco De Paoli, Alfredo Soldati We measure the effect of curvature of slender fibres on spinning rates in wall-bounded turbulence. The experiments are done in the TU Wien Turbulent Water Channel at $Re_{\tau}$ $180, \ 360$, and $720$. Fibre lengths range from below $1$ up to $20$ Kolmogorov lengths. Their aspect ratio ranges from $40$ to $120$. In these flow conditions they are neutrally buoyant, inertia-less, and rigid. |
Monday, November 21, 2022 9:18AM - 9:31AM Author not Attending |
L36.00007: Sedimenting array of ellipsoids: transient growth and nonlinear behaviour Rama Govindarajan, Harshit Joshi, Rahul Chajwa, Sriram R Ramaswamy, NARAYANAN MENON An array of ellipsoids sedimenting in a viscous fluid can avoid the well-known Crowley clumping instability of spheres and fall in a wave that couples orientational and translation degrees of freedom. In previous work [cite Chajwa2020] we established, by experiment, theory and simulation, the space of perturbation wave number and lattice spacing that separate this regime of linearly stable waves from the Crowley instability. We also showed that the non-normal character of the dynamical matrix leads to algebraic growth of perturbations ultimately destabilizing even the linearly stable waves. In this work, we explore the late-time behaviour in both regimes largely by simulations, with some illustrative experiments. We seek to understand whether clumps generically form regardless of the mechanism that first destabilizes the array, and if so, what statistical measures distinguish structures that grow through the (hitherto unexplored) nonlinear regime of the Crowley instability, and structures that develop from algebraic non-modal growth. |
Monday, November 21, 2022 9:31AM - 9:44AM |
L36.00008: Modeling the gravitational settling of microplastic fibers in the atmosphere Shuolin Xiao, Qi Li, Yuanfeng Cui, Donald L Koch, Natalie M Mahowald, Janice Brahney The ubiquitous presence of microplastics imposes multiple threats to the environment and ecosystem. There are extensive studies on their global cycles in the aquatic environment and increasing evidence from recent studies has highlighted the importance of the atmosphere as an equally important medium and transport pathway in the plastic cycle. The gravitational settling speed of microplastics, which is important to quantify the atmospheric limb of the plastic cycle, remains poorly understood, especially for asymmetrically-shaped microplastics such as fibers. It is estimated that microplastic fibers (MPFs) account for a significant portion of airborne and deposited microplastics found in both the natural and built environments with a more adverse effect on the health of organisms compared to nonfibrous ones. In this talk, a semi-analytical model of the gravitational settling velocity of MPF has been developed to include the effect of their morphology and ambient atmospheric turbulence. Particularly, in the framework of linearized slender body theory, the orientation variance of MPF that is the consequence of net balance among fluid convective inertia, rotational drag torque, and torque from turbulent strain has been parameterized to model the time-averaged MPF gravitational settling velocity. The results show that the settling speed of MPF is primarily determined by its cross-sectional configuration with nonnegligible dependence on ambient turbulence for certain types of MPFs, which is different from what is based on the volumetric equivalent spherical particle model. Specifically, flat fibers have an averaged approximately 80% reduction in dry deposition rate and enhancement of dry deposition lifetime above 500% compared with round fibers with their lengths and widths sampled from field measurement. |
Monday, November 21, 2022 9:44AM - 9:57AM |
L36.00009: Drag, lift, and moment coefficients for non-spherical particles in bounded and unbounded Flows at low to moderate Reynolds number Adel A Alghamdi, Isa Mohammed, Thomas Abadie, Omar K Matar Accurate predictions of hydrodynamic forces acting on a spherical and non-spherical particle are of fundamental importance in predicting the particle traveling velocity in a given flow. Traditionally, in simulations conducted for complex industrial particle-laden flows, a spherical particle shape is often assumed to simplify calculations even if particles are not spherically shaped. Spherical particles placed in bounded and unbounded flow have been extensively studied in the literature, while far fewer studies have examined the effect of the wall on predicting the coefficients of drag, lift, and moment for non-spherical particles; this is addressed in the present work using direct numerical simulations. Comparisons to data for spherical particles are carried out over a wide range of Reynolds numbers, particle-wall distance, and particle aspect ratio. The results suggest that spherical and non-spherical particles near the wall in shear bounded flow tend to have higher drag and moments than those away from the wall and those in unbounded flow conditions. Furthermore, the particles experience transverse lift affected by the presence of the wall driving them either away or closer to the wall. We also outline how these results can lead to the development of correlations for drag, lift, and moment coefficients for non-spherical particles which can be embedded in numerical codes for increased computational accuracy and efficiency. |
Monday, November 21, 2022 9:57AM - 10:10AM |
L36.00010: Sedimentation dynamics of deformable particles with small density difference to the surrounding fluid Isabell Noichl, Clarissa Schoenecker We present experiments of soft particles sedimenting from rest within a rectangular tank. Dur to their deformability, the particles may be subject to elastohydrodynamic interactions with the side walls of the tank, i.e. they might be subject to an extra lift or drag. The particles possess a small density difference to the surrounding fluid, such that the acceleration phase of the particles (until they reach a steady sedimentation velocity) is strongly extended. Depending on the particle's elastic modulus and the particle's position with respect to the wall, we find a variety of sedimentation patterns, in which the terminal sedimentation speed can be faster or slower than the classic Stokes velocity of a rigid sphere. Our findings provide input to the understanding and modeling of dynamics of particle sedimentation in bounded domains. They may be especially relevant for fields such as sedimentation of bioparticles or polymer particles, as in these cases, the density difference to the surrounding fluid can also be very small. |
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