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 C04: Interact: Particle-Laden Flows |
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Chair: S Balachandar, University of Florida Room: Ballroom D |
Sunday, November 24, 2024 10:50AM - 11:20AM |
C04.00001: INTERACT FLASH TALKS: Particle-Laden Flows Each Interact Flash Talk will last around 1 minute, followed by around 30 seconds of transition time. |
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C04.00002: Turbulent and Sedimentation Fluxes of Aerosols and Droplets in a Convection Cloud Chamber Steven K Krueger, Manikandan Rajagopal, Will Cantrell, Raymond A Shaw A laboratory convection cloud chamber, such as the Pi Chamber at Michigan Technological University, can produce a steady-state cloud of water droplets by mixing between a warm and wet lower boundary and a cool and wet upper boundary. The mixing is driven by turbulent Rayleigh-Benard convection. Cloud droplets form (are activated) by condensation on hygroscopic aerosols (such as NaCl) when the saturation ratio of water vapor exceeds a critical value. Conversely, droplets can evaporate and shrink (deactivate) into haze particles when the saturation ratio falls below the critical value. To form and maintain a steady cloud in the chamber, dry aerosols are injected at a constant rate. In a steady state, the rate of droplet fall out balances the rate of aerosol injection. The sedimentation speed of the particles in the chamber is much less than the typical turbulence velocity, so particle motion is largely random, yet it is droplet loss by sedimentation fluxes that balances the injection rate. This aspect, in combination with inhomogeneity of the saturation ratio, leads to regions of preferred droplet activation (sources) and deactivation (sinks), which produce surprising profiles of turbulent and sedimentation fluxes of aerosols and droplets in numerical simulations of a convection cloud chamber. |
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C04.00003: Mixed convection leads to significant vertical transport of settling particles Andrew P Grace, David H Richter Convection driven by an unstable temperature gradient can provide a means for significant vertical transport of dust grains and other aerosols. Moreover, in the presence of a mean shear, large scale streamwise-aligned roll structures appear. These rolls are a hallmark of what is known as mixed convection, and are known to efficiently transport heat and momentum vertically. However, it is not currently known how effective these rolls are for the vertical transport of inertial Lagrangian particles. To explore this, we highlight results from a series of coupled Eulerian-Lagrangian direct numerical simulations of mixed convection flows. By comparing free convection, no convection (a channel flow), and mixed convection, we highlight how coherent rollers appearing at a moderate Richardson number lead to significant vertical transport of settling inertial particles emitted near the lower surface. We find that inertial particles tend to cluster in regions associated with large vertical heat fluxes, and the result is a larger overall concentration in the interior of the domain when compared to both free convection, or pure channel flow. |
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C04.00004: Settling of actively buoyant particles Erika MacDonald, Nicholas Ouellette Not all particulate matter carried by fluid flows has constant buoyancy; in some cases, the buoyancy of a particle can change dynamically based on the surrounding flow. We refer to such an effect as "active buoyancy." Actively buoyant particles are found throughout nature. Examples include firebrands in wildfires, whose effective buoyancy is modulated conductive and convective heat transfer, or some marine microorganisms, which can vary their density to move up and down the water column. Although they are common, the dynamics of actively buoyant particles are not well understood. Thus, to begin to understand this complex problem, we will describe the results of a series of experiments that were conducted to investigate the effect of active buoyancy on particle settling. |
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C04.00005: A novel particle-induced instability of a simple shear flow Anu Viswanathan Sreekumari Nath, Anubhab Roy, Houssem Kasbaoui We investigate the instability of a dusty simple shear flow with non-uniformly distributed dust particles. While a simple shear flow is typically stable to infinitesimal perturbations, and a band of particles remains unaffected in the absence of background flow, we demonstrate that their combination can lead to destabilisation through two-way interactions. This instability arises solely from the momentum feedback from the particle phase to the fluid phase. We employ Eulerian-Lagrangian simulations to illustrate the presence of this instability and compare the results with a linear stability analysis using an Eulerian-Eulerian model. Our findings reveal that the instability is inviscid in origin and characterised by a critical wavelength below which it does not persist. |
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C04.00006: Interscale analysis of particle clusters amid turbulence Wai Hong Ronald Chan, Ahmed Elnahhas, Hanul Hwang, Lucy J Brown, S Balachandar The identification and tracking of clusters of loose, suspended particles in turbulent flows can be used to derive cluster statistics, determine cluster-dependent particle behavior, and understand the underlying turbulence (depending on the particle mass density). The formation of sediment clusters in coastal flows can cause optical occlusion, modulate the surrounding turbulence, and impact coral larvae settlement. The orientation of clusters relative to the mean flow can augment particle drag parameterizations. These loose clusters form, dissolve, and reshape just like dense particulate flocs agglomerate, break up, and restructure. Thus, statistics of loose particle clusters can shed light on the interscale nature of the underlying turbulence cascade. We apply an efficient number-density-based tree clustering method with basic similarities to DBSCAN to perform clustering for randomly distributed particles and particle-laden isotropic turbulence with near-unity Kolmogorov-scale Stokes numbers. Sensitivity of the power-law exponent of the cluster number distribution is reduced with appropriate choices of the proximity threshold and the minimum number of nearest neighbors per particle. Comparisons with the Voronoi and box-counting methods are performed. Individual particle tags are used to determine the continuity, breakup, and merger of particle clusters and evaluate particle fluxes along the phase-space coordinate of particle count to analyze interscale transport. |
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C04.00007: Particles clustering in water waves Varghese Mathai, Kerry O'Brien, Henry Jordan Inertial particles drifting through flows with multiscale eddies show rich dynamical properties, which have been a subject of extensive investigation. A simpler realization of the multiscale nature of the eddies is achieved by observing the motion of inertial particles drifting through a water wave field. Here we study inertial particles advected by a water wave. We observe a spatially locked distributions of evolving particle clusters. We characterize the clustering behavior of the particles and present a theoretical model to predict the behavior as function of particle and flow parameters. The results may be of relevance to understanding the transport and subsurface lifetimes of bubbles and microplastics. |
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C04.00008: Swelling soft hydrogel particles in turbulent Taylor-Couette flow: From particles in turbulence to jamming Detlef Lohse, Luuk J Blaauw, Sander G Huisman Using swelling soft hydrogel particles we study turbulent particle-laden flows with varying volume fraction from below 1% to 75%. We monitor the torque on the inner cylinder, temperature in the flow, particle size, and particle velocity throughout the entire swelling process of the particles. During the initial stages (small φ) the torque on the inner cylinder increases, connected to an increase in effective viscosity. At high volume fractions φ ≥ 0.55 the particles attenuate the Taylor vortices, decreasing the torque. At volume fractions φ ≥ 0.65 the flow changes to a pressure imposed flow, due to the increasing internal particle pressure, further increasing the torque. We obtain the particle velocity profiles and observe a shear band with a thickness of 1 particle close to the inner cylinder. At φ ≈ 0.75 the particles are unable to move with respect to each other and undergo as one block solid body rotation, where the only slip is at the smooth inner and outer cylinders. This work sheds new light on turbulent flows of dense suspensions near jamming and presents a new method to achieve high volume fractions in turbulent flows. |
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C04.00009: Investigating Inertial Spheres In a Flow Using Refractive Index-Matched Tomographic PIV Jibu Tom Jose, Aviel Ben-Harush, Gal Friedman, Dvir Feld Feld, OMRI RAM A series of refractive index-matched, time-resolved tomographic PIV experiments are performed to study the dynamics of inertial spheres in a flow. Using a 62% aqueous sodium iodide solution matching the refractive index of acrylic spheres, we achieve unobstructed optical access, enabling simultaneous recording of 3D flow fields and fluid-structure interactions. Two cases are presented: (1) spheres in a round channel with abrupt area changes and (2) spheres rising in quiescent flow at terminal velocity. |
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C04.00010: Ejecta distribution and dynamics during high-speed jet impingement on granular surfaces. Nicolas Rasmont, Liam Heuser, Joshua Rovey, Laura Villafane High-speed rocket plume impingement on soil surfaces poses major risks during planetary landing missions. Plume-surface interactions (PSI) can create deep craters and dense clouds of high-speed ejecta, potentially blinding instruments and damaging vehicles and nearby assets. These effects are highly sensitive to flow and soil parameters. We present results from sub-scale PSI experiments conducted at representative Lunar and Martian ambient pressures, varying flow non-dimensional parameters and nozzle elevation. Our focus is on ejecta dynamics and concentration distributions, using glass microspheres as a canonical soil simulant. We employ two measurement techniques: planar Particle Tracking Velocimetry and mm-wave tomography. These measure ejecta trajectories and velocities in a vertical plane containing the jet axis, and ejecta concentration at two surface-parallel planes, respectively. By combining these measurements with particle trajectory models in an optimization framework, we replicate the complete ejecta cloud evolution. This allows us to determine key quantities such as mass transport and kinetic energy from the surface, and estimate far-field ejecta properties. |
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C04.00011: Slender flexible fibers in wall-bounded turbulence Cristian Marchioli, Davide Di Giusto, Darish Dhas We study the dynamics of flexible fibers in turbulent channel flow by performing direct numerical simulations at shear Reynolds numbers up to Re=1200 and tracking fibers with large aspect ratio (AR, up to 200), length L extending up to the inertial range of the flow, and Stokes numbers spanning two orders of magnitude (from St= 0.1 to St=11). For each combination of (AR, L, St) values, different fiber rigidities are considered to compare fibers with moderate stiffness (Young modulus EY=105 in dimensionless units) with stiff-less ones (EY=0). We also account for the effects of fluid inertia on the forces and torques experienced by the fibers, thus going beyond the commonly used Jeffery torques. We focus on the conditions under which the inertial contribution becomes relevant given the intermittent nature of the flow, comparing the drift time (order of a few periods of rotation) with the typical time of the fluid velocity fluctuations. We show that the fibers in the bulk of the flow orient with the local strain, align with the vorticity - as in homogeneous isotropic turbulence - and experience a tumbling rate comparable to that of rigid fibers. Near the walls, vorticity orients with the spanwise direction while flexible fibers align with the mean flow. This orthogonality determines a stronger contribution of the flow rotation to the tumbling rate. The most probable deformed shapes define a bi-variate probability space, suggesting that two main deformation patterns exist: eyelash bending and compressive buckling. |
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C04.00012: Breaking symmetries in chiral sedimentation Greg A Voth, Meera Das, Elias Huseby, Pierre Mathier, Arjun Menezes We experimentally study the design of chiral shapes to optimize translation-rotation coupling in Stokes flow. Helical ribbons serve as a simple reference geometry which is co-centered and has strong translation-rotation coupling. During sedimentation, helical ribbons follow periodic orbits in orientation with complex quasi-periodic orbits in space. Adding a center of mass offset by inserting metal spheres in the 3D printed ribbons breaks co-centered symmetry and produces a wide range of dynamics including closed orbits, convergence to attracting orientations, and limit cycles. In experiments and numerical simulations, we measure the stability balloon in the space of 3D center-of-mass offsets where a bifurcation occurs that separates particles with complex dynamics from those with larger center of mass offsets that converge to a single orientation in tilt-spin space.
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C04.00013: Effect of particle size on turbulence modulation in Particle Resolved DNS of a turbulent neutrally buoyant particle-laden channel Jonathan Van Doren, M. Houssem H Kasbaoui The modification of turbulent structures by finite size particles is of interest to pipeline design for oil and slurry transport. The role of particle size in turbulence attenuation or enhancement is poorly understood. We investigate the interaction of finite size particles with turbulent flow structures in Particle-Resolved Direct Numerical Simulations of turbulent channel flow at friction Reynolds number 180, laden with neutrally buoyant, spherical finite size particles, dispersed at volume fraction 10%. Particle diameter is varied from 20.2 to 40.4 wall units, in order to elucidate the role of particle size in turbulence modulation. We use the recently developed volume-filtering immersed boundary method to track and represent between 4650 and 600 resolved particles, which accounts for stresses at the fluid solid interface. Additionally, we collect turbulence statistics from a particle free channel for comparison with the particle laden channels. |
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C04.00014: Fingerprints of Turbulence in the Deposition Patterns of Charged Particles Matt T Gorman, Miguel X. X Diaz-Lopez, Xuan Ruan, Rui Ni Particle deposition in wall-bounded flows, driven by the surrounding turbulence via the turbophoresis process, is augmented when particles are charged. This augmentation occurs in many familiar applications, including dust/ash ingestion in aircraft engines where particles are charged triboelectrically and electrostatic precipitation for filtration technologies where particles are charged from an external ionization source. However, the coupling between turbulence and electrostatic effects in the deposition problem and the conditions under which each effect dominates are still poorly understood. To explore this coupling, experiments were conducted in a vertical turbulence channel equipped with a high voltage ionization wire to prescribe electrostatic charges to the particles. Both the deposition on the wall and the velocity statistics of entrained particles approaching the wall were captured with high-speed cameras. Deposited particles were observed to form patterns with similar streaking features as particles in the viscous layer, which are known to preferentially concentrate in low momentum streaks. Furthermore, the global deposition rate is found to be strongly dependent on the velocity statistics of the entrained particles, which in turn show a strong sensitivity to the particle charge. |
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C04.00015: Impact of snow morphology and atmospheric turbulence on snow settling behavior Michele Guala, Jiaqi Li, Jiarong Hong Measuring and predicting snow settling velocity is essential for improving ground snow accumulation estimates in weather forecast models. Both variability in snowflake morphology (dendrites, plates, needles, graupels, aggregates) and atmospheric turbulence significantly influence the settling velocity. To elucidate these mechanisms, we conducted a comprehensive study under various field conditions deploying a three-dimensional particle tracking velocimetry system and a snow particle analyzer. These tools allowed us to measure particle settling trajectories, characterize snowflake size, shape, and density, and estimate their aerodynamic properties. Our previous work on snow settling in mild turbulence highlighted the significant impact of non-spherical snow shapes in modulating the settling velocity. We observed pronounced meandering motions in dendrites and aggregates, which affects their trajectories curvature. These meandering motions also lead to orientation changes of snow particles, causing reduced average projected area and enhanced settling velocity. Analyzing settling trajectories under more intense atmospheric turbulence, we observed converging acceleration statistics across various snowflake morphologies, and a more pronounced turbulence effect on the particle fall speed. Our findings offer key insights for modeling snow settling velocity, considering morphology and turbulence impacts determined by settling parameter (SvL) and Stokes number (Stη). |
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C04.00016: Enhancement and reduction of particle settling velocity in homogeneous turbulence Marcel Wedi, Matteo Clementi, Rafael Bölsterli, Filippo Coletti The settling of inertial particles in turbulent flows, relevant for environmental and engineering settings alike, is complicated by the stochastic nature of the carrier-phase flow and dispersed-phase distribution. Turbulence can both enhance or reduce the mean settling velocity, and predicting the dominant mechanisms is an ongoing challenge. |
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C04.00017: An inertial slender-body theory to characterize particle-fluid interactions at finite Reynolds numbers Anmol Joshi, Anubhab Roy, Donald Lyle Koch We present a fully inertial slender-body theory to study the effects of moderate to large fluid inertia on |
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C04.00018: Numerical analysis of non-spherical particles in particle-wall, particle-particle, and particle-fluid interactions Tiffany Simmons, Mohsen Daghooghi, Iman Borazjani Non-spherical particles within a fluid suspension can be difficult to experimentally analyze. This study presents a numerical analysis of non-spherical particle-particle, particle-wall, and particle-fluid interactions. The sharp-interface curvilinear immersed boundary (CURVIB) method is employed to simulate particle-fluid interactions. The kinematic equations of motion are utilized to model particle dynamics, while a threshold algorithm is used to detect particle-wall and particle-particle collisions. Collision is modeled by employing conservation of momentum and the coefficient of restitution to ensure physical behavior. Verification studies for (no fluid) simulations confirm that the total energy is conserved when the coefficient of restitution is equal to one for both particle-particle and particle-wall collisions. By investigating particle interactions and dynamics within a fluid, we can achieve a better understanding of particle behavior across various fields. |
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C04.00019: ABSTRACT WITHDRAWN
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C04.00020: Turbulence modulation with controlled particle injection and their migration Partha S Goswami, Pradeep Muramulla, Viswanathan Kumaran Characterizing turbulence modulation in particle-laden turbulent flows is an active area of research. It has been observed that there is a discontinuous collapse of turbulence at a critical volume fraction [1]. At this critical volume fraction, there is a reduction of second moments of all the components of fluid velocity fluctuations by 1–2 orders of magnitude. The study revealed that this transition is a robust one, and the state beyond the critical volume fraction is a laminar state with fluid velocity fluctuation generated by the force exerted by the particle phase. An analysis of the fluid momentum equation revealed a sharp decrease in the divergence of Reynolds stress at the critical volume fraction. Similarly, in the energy equation, there is a dramatic decrease in the turbulent energy production rate at the transition volume fraction. However, there is a small decrease in the energy dissipation rate due to the mean flow and a small increase in the dissipation rate due to the particle drag. The results indicated that a decrease in the rate of turbulence production is the main reason behind the turbulence collapse. Such an observation motivated us to investigate whether turbulence modulation is possible by controlled particle injection at the zone of the channel where turbulence production is maximum. A series of DNS has been conducted by injecting particles in a controlled manner at particular zones of the channel as well as controlling their cross-stream migration. It is observed that when the particles are injected only at the zone of maximum turbulence production, there is a maximum 20% decrease in turbulent fluctuation, and the extent of turbulence attenuation is maximum when the particle migrates up to a maximum cross-stream distance, even at a lower solid volume fraction. |
Sunday, November 24, 2024 11:20AM - 12:50PM |
C04.00021: INTERACT DISCUSSION SESSION WITH POSTERS: Particle-Laden Flows After each Flash Talk has concluded, the Interact session will be followed by interactive poster or e-poster presentations, with plenty of time for one-on-one and small group discussions. |
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C04.00022: ABSTRACT WITHDRAWN
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