Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session L41: ParticleLaden Flows: ParticleTurbulence Interactions II 
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Chair: Mona Rahmani, University of British Columbia Room: 206 
Monday, November 20, 2023 8:00AM  8:13AM 
L41.00001: Sedimentation of microplastics due to their aggregation with biogenic particles in turbulent flows Mona Rahmani, Masoud Rezaeian, Federico Pizzi, Joan Grau Barcelo, Francesco Capuano, Lluis Jofre In this study we investigate the enhancement of sedimentation of microplastics due to their aggregation with biogenic particles in homogeneous and isotropic turbulence using direct numerical simulations and Lagrangian tracking of point particles. The prevalence of microplastics (plastic particles less than 5 mm in size) in oceans and lakes has been a growing environmental concern in the past decade. Only a small fraction of the microplastics that are estimated to enter the ocean, or generated in the oceans through the fragmentation of larger pieces, are found to be floating on the ocean surface. The missing of microplastics from the ocean surface has been attributed to the aggregation of microplastics with heavier biogenic particles. In this regard, we investigate how the combined effects of differential settling/rising of microplastics and biogenic particles and turbulent flow motion contribute to the aggregation of microplastic and biogenic particles for different settling numbers and Stokes numbers. Additionally, we quantify the composition of the aggregates and the rate of settling of microplastics due to the formation of the aggregates. 
Monday, November 20, 2023 8:13AM  8:26AM 
L41.00002: Roughness effect on particle laden turbulent channel flow Mehul Kumar, Pradeep Muramulla, Partha Sarthi Goswami, Kumaran V Particleladen turbulent suspensions of inertial particles are ubiquitous, occurring naturally as well as in industries with highly inertial particles. Fluid Turbulence gets attenuated with relatively small size particles, whereas it gets amplified for larger size particles. It has been reported that turbulent disruption happens discontinuously for wallbounded flows. The objective of the present study is to quantify the effect of particle and wall roughness on turbulence modulation. Pointparticle Direct numerical simulations (PPDNS) are carried out for a vertical channel, including the roughness in particleparticle and particlewall interactions. The Reynolds number based on the channel width and average airflow velocity and viscosity Re = 5600 is considered. The particle Reynolds number based on the particle diameter and root mean square of the difference in the particle and fluid velocities is in the range of 4–15. The particle volume fractions are 0–3.5×10^{3}, and the particle Stokes number is 200. It is observed that irrespective of the nature of particleparticle interactions, only the particlewall interaction majorly controls the dynamics of the flow inside the system. With an increase in the roughness between wallparticle interaction, the second moments of the velocity fluctuations increase. However, the particle mean velocity decreases, and fluid velocity becomes more flat at the center core. The rough particlewall interaction leads to an early collapse in the fluid phase turbulence. 
Monday, November 20, 2023 8:26AM  8:39AM 
L41.00003: Settling dynamics of Kolmogorov scale sediment particles in homogeneous isotropic turbulence Nathan Keane, Sourabh V Apte Settling dynamics of slightly heavierthanfluid particles in turbulence is of critical importance for suspended sediment transport. Of particular interest is the mean particle settling velocity in turbulence which can be influenced by fast tracking, vortex trapping, and loitering mechanisms. A pointparticle model based on the complete MaxeyRiley equation is used to investigate settling dynamics of particles in vortical flows. First, particles settling in a stationary TaylorGreen vortex is investigated by varying the vortex strength relative to the particle settling speed in quiescent flow. For medium vortex strength, the settling speeds are observed to decrease due to loitering and vortex trapping effects. Fast tracking dominates and increases the settling speed for higher vortex strengths. This behavior is further investigated in a twoway coupled, forced, homogeneous isotropic turbulence by varying the turbulence intensity relative to the settling speed in quiescent flow for multiple Stokes numbers, in order to characterize the settling dynamics of Kolmogorovscale particles. Mechanisms that influence the settling dynamics for a range of turbulence intensity and particle Stokes numbers are identified. 
Monday, November 20, 2023 8:39AM  8:52AM Author not Attending 
L41.00004: Abstract Withdrawn

Monday, November 20, 2023 8:52AM  9:05AM 
L41.00005: Inertial chiral particles affect homogeneous turbulence vorticity Giulia Piumini, Martin Assen, Detlef Lohse, Roberto Verzicco We present results from direct numerical simulations of chiral finitesize inertial particles, under the effect of gravity in a triperiodic domain with homogenous isotropic turbulence. Although the interest in turbulent inertial particleladen flows has increased in the last decade, most of the previous studies have mainly focused on highly symmetrical particles (i.e. spheres or ellipsoids) either with or without inertia. In this study we introduce chiral and convex particles whose size is in the turbulence inertial range. 
Monday, November 20, 2023 9:05AM  9:18AM 
L41.00006: The Effect of Particle Collisions on Heat Transfer in a Thermally Developing Mixing Layer in a Dilute Turbulent ParticleLaden Flow Hamid Reza Zandi Pour, Michele Iovieno We present a study on the influence of interparticle collisions on the turbulent heat flux within a temporally developing thermal mixing layer between two homothermal regions in a homogeneous and isotropic turbulent velocity field. We carry out twoway thermally coupled EulerianLagrangian Direct Numerical Simulations across a wide range of particle Stokes numbers, ranging from 0.2 to 3, at a Taylor microscale Reynolds number from 56 up to 124, while maintaining a thermal to kinetic relaxation times ratio of 4.43. The particle concentration in the dilute regime is set at 4x10^{4} volume fraction. 
Monday, November 20, 2023 9:18AM  9:31AM 
L41.00007: Turbulence modification of particleladen flow in horizontal rectangular duct Sourav Ganguli, Partha S. Goswami, Manaswita Bose Pneumatic conveying is used to transport solids in many chemical and pharmaceutical industries. Despite its high industrial relevance, the different types of interactions, like the particle–turbulence, particleparticle, and particle–wall for wallbounded flows, are not well understood. The objective of the present work is to understand the twophase dynamics of the particleladen flow in a horizontal rectangular duct. Simulations are performed using the EulerianLagrangian framework considering turbulent fluid medium as the continuum, and the particles are discrete Lagrangian point particles. Although point particle approximation is used to calculate drag force on the particles, their finite size effect is considered to simulate particleparticle and particlewall interactions. The duct used in the present investigation has a crosssection of 4:1. Twoway coupling is used with the DeFelice equation to model the drag. Dynamic one equation LES is coupled with DEM for the particle phase. Simulations are performed using both perfectly smooth and rough particles, where linear springdaspot model is used considering normal coefficient of restitution of 0.9. The mean velocity profiles for the gas and particle phases and the second moments of the velocity fluctuations are computed. It is observed that the fluid Reynolds stress decreases with the increase in the mass loading ratio, and a turbulence collapse is observed for the mass loading ratio of 1.0 when the particle Stokes number is 82. 
Monday, November 20, 2023 9:31AM  9:44AM 
L41.00008: The Effect of Subgridscale Turbulence on LES of Inertial Particle Transport in a Boundary Layer Flow Iago DalRi dos Santos, Neda Yaghoobian Investigation of particle dispersion in boundary layer flows is of great importance in several environmental applications, such as atmospheric pollutant dispersion and ember tracking during wildfires. In these and many practical cases, the accurate tracking of particle trajectories across large spatial and temporal scales requires the use of Large Eddy Simulations (LES). However, one of the main limitations of LES is its inherent filtering of smallerthanfilter size (subgridscale (SGS)) flow features, which can compromise the accuracy of particle transport models. These filteringinduced inaccuracies accumulate over time, leading to increasingly higher errors as the spatial and temporal scales of the simulation increase. In this work, we employ a structural SGS model to account for and investigate the effects of subgrid turbulence on the transport of particles in a boundary layer flow. We focus our analysis on settling particles of different sizes, while identifying the mechanisms governing their distribution within the flow. When comparing against Direct Numerical Simulations, the SGS model improves both flow and particle statistics, leading to a better prediction of landing distributions across a wide range of particle sizes. 
Monday, November 20, 2023 9:44AM  9:57AM 
L41.00009: A continuous random walk approach for stochastic modeling of particles dispersion and deposition using LES Farid Rousta, Goodarz Ahmadi, Bamdad Lessani A stochastic continuous random walk approach (CRW) method is used to model the subgridscale (SGS) velocity fluctuations seen by particles for largeeddy simulation of particleladen flow. An EulerianLagrangian approach was used for particles with the range of Stokes numbers from St = 1 to 24. First, particle statistics are reported where the filtered directnumerical simulation (FDNS) velocity is used in the Lagrangian equations of solid particles without a subgridscale velocity fluctuation model. The DNS data are filtered by applying a sharp spectral filter to the turbulent velocity field. Comparative analysis of particulate phase results before and after filtering revealed a significant impact of SGS velocity fluctuations on particle dispersion and deposition within the channel. Subsequently, SGS fluctuations generated by the stochastic CRW model were added to the filtered velocity in the Lagrangian equation of particles. With the inclusion of a drift term and a proper Lagrangian time scale in the CRW equation, the method can accurately predict particle statistics. The particle deposition velocities for the range of Stokes number are validated against experimental data and DNS simulations. The results showed that the appropriate stochastic CRW model could correctly predict the SGS velocity fluctuations and enhance the accuracy of the LES of turbulent particleladen flows. 
Monday, November 20, 2023 9:57AM  10:10AM 
L41.00010: Turbulence transport in particleladen compressible flows Jesse Capecelatro, Archana Sridhar, Rodney O Fox Turbulence transport in compressible dispersed twophase flows is complicated by strong coupling between velocity fluctuations, shock waves, and particles. In this talk, highlyresolved numerical simulations are employed to quantify turbulence transport mechanisms and guide the development of a reducedorder model. Two canonical flows are considered: (i) compressible flow through homogeneous suspension of particles and (ii) a planar shock interacting with a cloud of particles. Turbulent kinetic energy (TKE) is found to contribute to a significant portion of the resolved kinetic energy, as much as 100% at the highest volume fractions considered. The TKE budget reveals turbulence is primarily produced via drag and is hindered by gasphase compressibility. A twoequation model is proposed and implemented within a hyperbolic Eulerianbased twofluid model. The model is found to be accurate across a wide range of volume fractions and Mach numbers in both homogeneous and inhomogeneous flows. 
Monday, November 20, 2023 10:10AM  10:23AM 
L41.00011: Experimental investigation on dynamics of charged bidisperse particles in turbulence Xuan Ruan, Matt Gorman From tribocharged particles in sandstorms, the dust lightening after volcanic eruptions, to the removal of particulate pollutants in the flue gas, the dynamics of charged particles in turbulence is important to a wide range of natural and industrial applications. Compared with neutral particles, the presence of electrostatic force could significantly modulate particles dynamics and cause abundant phenomena. In this talk, we present an experimental study of the dynamics of oppositely charged bidisperse particles in homogeneous isotropic turbulence. The spatial distribution of charged particles is first measured to show the global effects of electrostatic force on particle distribution in turbulence. For particle trajectories close to each other, the relative motion is further analyzed to show the dominant influence of the electrostatic force over short distances. Finally, a theoretical analysis is presented to quantify the competition between the electrostatic force and the hydrodynamic interaction, which contributes to a more complete physical understanding of charged particleladen flows. 
Monday, November 20, 2023 10:23AM  10:36AM 
L41.00012: The Settling Rates of Particles in Rayleigh–Bénard Turbulence Kristin SwartzSchult, Jesse C Anderson, Hamed Fahandezh Sadi, Swafuva Varappillikudy Sulaiman, Will Cantrell, Raymond A Shaw, David H Richter

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