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 Q36: Particle-Laden Flows: Non-Spherical and Deformable Particles II |
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Chair: Gretar Tryggvason, Johns Hopkins University Room: 244 |
Monday, November 21, 2022 1:25PM - 1:38PM |
Q36.00001: Rheology and microstructure of a particle-laden soap film Jonathan Lalieu, Antoine Seguin, Georges Gauthier Particle-stabilized foams have proven to be materials with promising mechanical properties for the construction industry: individual particle-covered bubbles in the form of gas marbles are able to undergo large over- and under-pressure. However, their rheology has yet to be formally described. We study experimentally the rheological behavior of a particle-laden soap film as a macroscopic 2D model suspension: a tetradecyl trimethyl ammonium bromide (TTAB) solution in a water-glycerol mixture is made to form the liquid soap film in which we trap slightly polydisperse polystyrene beads. The solid particles' diameter (Ø 80 µm) is larger than the typical thickness of the film, the surface tension then gives rise to attractive forces. We perform the study at controlled shear-rate in an original simple shear geometry and highlight, at high-particulate fraction, a visco-plastic behavior. We then compare these results to local measurements of the shear-rate obtained through image correlation, thus revealing the inhomogeneity of the shear. An extended kinetic law captures it well, as well as providing us with a theoretical origin for a boundary-dependent diffusion length of the rearrangements, associated with a transition in the orientational order in the microstructure. |
Monday, November 21, 2022 1:38PM - 1:51PM |
Q36.00002: Buoyant, non-spherical particles in turbulent wind-driven waves Lucia Baker, Anusha Aggarwal, Julio E Chávez-Dorado, Inessa Garrey, Michelle H DiBenedetto Buoyant particles, such as microplastics, debris, and ice crystals, are ubiquitous at the surface of the ocean. However, it is not known how particle size, shape, and inertia interact with wind-driven turbulence and waves at the free surface to affect their transport and dispersion in the water column. Experiments are performed to measure particle depth and orientation in a laboratory wind-wave tank over a range of wind speeds relevant to the ocean surface. Buoyant rod-, disk-, and sphere-shaped HDPE particles are seeded in the flow, and particles are tracked using a large-scale shadow imaging technique. The results provide insights into the physical processes governing particle transport in the ocean surface layer. Particle diffusivities are calculated from Lagrangian statistics and compared to observed concentration profiles. Orientation is investigated as a function of depth, and we find that particles have variable orientations near the surface of the water but adopt a preferential orientation deeper in the water column. This bimodal behavior suggests competing forcing on particle orientation due to buoyancy, turbulence, and waves. |
Monday, November 21, 2022 1:51PM - 2:04PM |
Q36.00003: Numerical modeling of dispersion of non-spherical particles by waves and currents Laura K Clark, Michelle H DiBenedetto, Nicholas T Ouellette, Jeffrey R Koseff We numerically investigated the dispersion of non-spherical particles in a wave-current flow, with a focus on determining how various parameters, grouped into nondimensional numbers, impact dispersion. We performed simulations of negatively buoyant ellipsoids falling from the surface of a wave-current flow with varied initial particle orientation and wave phase. We examined the impact of the following nondimensional numbers on particle dispersion, which together fully describe the input parameter space for this system according to the Buckingham Pi theorem: the Archimedes number, the Stokes number, the particle eccentricity, the Keulegan-Carpenter number, the ratio between the Stokes drift and particle settling time scales, and the wave steepness. We found that no single parameter dominated the dispersion, and that no single nondimensional number could fully explain the results; nearly all of them were significant in determining the dispersion. Our results have ramifications for modeling the transport of microplastics near the surface of the ocean. |
Monday, November 21, 2022 2:04PM - 2:17PM |
Q36.00004: Physical Beaching Process of Microplastic Particles from Regular Waves Ben Davidson, Nimish Pujara Microplastic pollution is a significant problem around the globe. However, the transport dynamics of these particles are not well understood, specifically with how microplastics accumulate in coastal and beach environments. We consider the physical beaching process for microplastic particles due to incident waves through laboratory wave flume experimentation. With buoyant plastic rods and disks starting near the still water line on an impermeable beach, the particle responses are observed during incident regular waves. Previous experiments have shown that for flow driven by solitary waves, the proximity of the particle starting location to the still water line influences the particle fate with respect to beaching. We implement surface particle image velocimetry (PIV) to measure the flow field velocity in the swash zone. We combine PIV data with particle tracking measurements of the plastic rods and disks to calculate the slip velocity of the flow on the particles. We aim to observe the dynamics dictating the fate of non-spherical nearshore plastic particles and quantify the statistics of plastic particle beaching based upon the parameters of incident waves and the particle Stokes number. |
Monday, November 21, 2022 2:17PM - 2:30PM |
Q36.00005: Orientation dynamics of a slender particle in simple shear flow of a viscoelastic fluid: Theory and direct numerical simulations Arjun Sharma, Donald L Koch Previous experiments indicate that viscoelasticity changes the initial condition dependent orientation dynamics of a slender particle in a Newtonian Stokes flow (Jeffery orbits) in myriad ways. Previous theories suggest only one type of motion due to viscoelasticity, where the particle spirals towards the vorticity axis for all initial conditions. Using regular perturbation in polymer concentration and a generalized reciprocal theorem, we construct a theory to explain the effect of viscoelasticity on the motion of a large aspect ratio prolate spheroid in an Oldroyd-B viscoelastic fluid. The orientation trajectories from this theory show a better qualitatively match with the previous experimental observations. Depending on the polymer concentration, relaxation time, and the particle aspect ratio, the particle may end in a small periodic orbit close to the vorticity axis or obtain a stable orientation near the flow direction. A particle near the flow-gradient plane may either spiral or drift monotonically along the flow-vorticity plane. We test our theory and investigate higher polymer concentration effects using a novel finite-difference numerical solver written in prolate spheroidal coordinates, which exactly models the particle surface as one of the coordinate surfaces. |
Monday, November 21, 2022 2:30PM - 2:43PM |
Q36.00006: Tumbling of quasi-straight to slightly curved fibers in channel flow turbulence Mobin Alipour, Marco De Paoli, Alfredo Soldati In this study, we investigated the tumbling dynamics of quasi-straight to slightly curved fibers via ''adaptive filtering'' and we have been able to report a universal scaling for the tumbling rate of the fibers. Fibers used in this study are in order of (1-2) times of Kolmogorov length scale of the flow for the lowest Reynolds number examined. Results for the channel center, the most homogeneous part of the flow, are compared and benchmarked with previously reported tumbling rates for straight rods in Homogeneous Isotropic Turbulence (HIT). We addressed the hypothesis which relies on simplifying the dynamics of slightly curved fibers as straight fiber and show that this is possible only by using a correction factor which is defined based on an analytical model reported by Hinch & Leal (1979). By means of this correction factor, we show that the magnitude of the tumbling rate for quasi-inertialess fibers is independent of fibres asymmetry rate and location in channel height. |
Monday, November 21, 2022 2:43PM - 2:56PM |
Q36.00007: Disks settling in turbulence: an experimental study Amy Tinklenberg, Michele Guala, Filippo Coletti The settling dynamics of plate crystal hydrometeors in nature are influenced by atmospheric turbulence. Quantifying the change in settling behavior due to the turbulence is necessary to fully understand and ultimately predict frozen hydrometeor settling under given atmospheric conditions. In this study, a large experimental air chamber is used to produce various turbulence intensities. Solid disks with comparable size and density ratio to plate crystals in the atmosphere are released into the chamber at controlled volume fractions. Through planar imaging, time‑resolved images are captured and are analyzed to obtain translational and rotational quantities of the disk motion. Results at two turbulence intensities are compared to those under quiescent conditions to examine how adding turbulence to the system affects the settling behavior. Under turbulent conditions, the non-tumbling (stable) falling style is eliminated and an increasing trend in tumbling angular velocity with increasing disk size becomes prominent at the highest turbulence intensity considered. Additional experiments with a perforated disk geometry are briefly introduced along with some initial results. |
Monday, November 21, 2022 2:56PM - 3:09PM |
Q36.00008: Studies of the Dynamics of Suspensions of Ellipsoidal Particles Jiacai Lu, Xu Xu, Shijie Zhong, Rui Ni, Gretar Tryggvason The dynamics of suspensions of prolate ellipsoidal solid particles in a small periodic domain is studied by fully resolved numerical simulations, for relatively modest Reynolds numbers and a density ratio of ten. After describing the numerical method briefly, we examine the effect of volume fraction as it is changed from two to ten percent. The results show a transition from flow dominated by the hydrodynamic interactions between the particles and the fluid, although modified by collisions, at low volume fractions, to flow dominated by collisions at higher volume fractions. At low volume fraction, most of the particles fall broadside-on whereas, at the highest volume fraction, their orientations are essentially random. The distribution of the particles with respect to each other, as measured by the probability distribution of nearest distance, on the other hand shows a nearly random distribution at low volume fractions but at high volume fractions there is more clustering than for a random distribution. Results for different shapes, including oblate ellipsoids and spheres, and different Reynolds numbers and density ratios, are also discussed. This rich dataset will help us determine how the forces on each particle depend on the local flow structure. |
Monday, November 21, 2022 3:09PM - 3:22PM |
Q36.00009: Orientation dynamics of a spheroidal particle settling in a simple shear flow Himanshu Mishra, Anubhab Roy In a viscous simple shear flow, a force-free, torque-free spheroid executes a periodic rotary motion - known as Jeffery orbits. However, the orientation of a sedimenting axisymmetric particle is indeterminate in the Stokesian regime. The indeterminacy is removed with the inclusion of fluid inertia, wherein an inertial torque leads to a spheroid falling with a broadside-on orientation. In the current study, we explore the competition of the two torques, shear and inertial, for a spheroid settling in a simple shear flow. Two non-dimensional quantities span the parameter space - the ratio of flow to settling time-scale (S_{F}) and the angles subtended by the vorticity axis of the flow to gravity (α, β). The orientation phase-space exhibits a rich dynamical behavior as we scan through S_{F}, α, and β values. The bifurcation diagrams reveal the transition from an oscillating orientation angle to a constant fixed angle predicted from larger sedimentation torques. |
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