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 X02: Minisymposium: Inertial Particles in Inhomogeneous Turbulent Flows |
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Chair: Alberto Aliseda, University of Washington Room: Ballroom B |
Tuesday, November 26, 2024 8:00AM - 8:26AM |
X02.00001: Inertial particles in a turbulent/turbulent interface Invited Speaker: Amelie Ferran Over the last three decades, the main advances in the understanding of particle-turbulence interactions have come from the study of a canonical flow: homogeneous isotropic turbulence. However, most flows in nature feature non-homogeneous turbulence with a turbulent interface separating two regions of different turbulent intensities (turbulent/non-turbulent or turbulent/turbulent). Although there are several studies on the dispersion of inertial particles in free-shear flows, few experiments have focused on the entrainment of particles by a turbulent interface. In the present study, we present the effect of a sheared turbulent/turbulent interface on the particles' clustering properties and settling velocity modification. With wind tunnel experiments, a high gradient of turbulence intensity is introduced in the sheared turbulent flow collocated with the particle injection. Particles are transported from the turbulent side, with higher turbulence intensity, to the low-intensity side by large-scale-energetic eddies. The physics of entrainment in the T/T interface also result in an enhancement of particle preferential concentration and settling velocity, consistent with the extended interaction of those particles with turbulent structures across the entire turbulent spectrum. |
Tuesday, November 26, 2024 8:26AM - 8:52AM |
X02.00002: Modeling of inhomogeneous particle-laden turbulence Invited Speaker: S Balachandar Substantial past effort has focused on developing accurate models of particle-fluid force coupling and subgrid Reynolds stress closures that can be used in Euler-Lagrange and Euler-Euler simulations, but mostly in the homogeneous limit when particles are uniformly distributed and subjected to a uniform form. The focus of this talk will be to account for the effect of inhomogeneity that arises both from the non-uniform distribution of particles as well as spatial variations in the mesoscale flow. Characterization of such inhomogeneity must involve parameters such as volume fraction gradient and velocity gradient tensor, in addition to mean particle Reynolds number and volume fraction. A summary of current understanding and most promising future directions will be discussed. |
Tuesday, November 26, 2024 8:52AM - 9:18AM |
X02.00003: Vertical dispersion of buoyant particles in a free surface flow Invited Speaker: Michelle Heather DiBenedetto Microplastics are buoyant particles that accumulate at the ocean surface. In this talk we consider the vertical transport and mixing of buoyant particles below the free surface |
Tuesday, November 26, 2024 9:18AM - 9:44AM |
X02.00004: Split and Unite: How Turbulence Shapes Bubble Populations Invited Speaker: Rui Ni Turbulence exhibits a fascinating duality in its effect on bubble populations, simultaneously driving two seemingly opposing processes: the fragmentation of large, otherwise stable bubbles and the coalescence of smaller ones through collision. This dynamic interplay gives rise to the polydispersed bubble clouds observed in diverse settings, from breaking waves to chemical, biological, and nuclear reactors. At the heart of this phenomenon lies a critical question: What are the characteristic timescales of breakup and coalescence in turbulence? The complexity of this inquiry stems from the vast range of scales involved, spanning from the Kolmogorov scale to individual bubble diameters and up to the turbulence integral scale. In this talk, we introduce a comprehensive experimental framework designed to capture these two multiscale processes. Our approach aims to shed light on the general mechanisms governing deformable objects, including both droplets and bubbles, in turbulent environments, with a particular focus on the timescales and length scales involved in breakup and coalescence events. By elucidating these processes, we seek to contribute to the development of new models capable of accurately capturing bubble and droplet population dynamics in key applications. |
Tuesday, November 26, 2024 9:44AM - 10:10AM |
X02.00005: Cluster and inertial particle dynamics in turbulent channel flows Invited Speaker: Laura Villafane Turbulent flows laden with small inertial particles exhibiting preferential concentration are time varying inhomogeneous systems from a macroscopic perspective, with a fluctuating particle concentration field that can modulate other phenomena relying on local concentration or path integrated quantities. Particle local concentration can reach values many times the average concentration, with clusters that vary in size, from the dissipative to the integral turbulence length-scales. Important to physical processes mediated by clustered particles are also the timescales in which particle clusters remain spatially coherent. In this talk we will provide an overview of recent work by our group on vertical turbulent channel flows laden with particles, including data analysis methodologies, experimental methods, and discussion of results for varying flow and particle parameters. We focus on particles denser-than-fluid and smaller than the dissipative scales, and mostly in dilute regimes, to analyze the effect of particle to flow time scales ratio (St) and the contribution of gravitational effects. In particular, we will present time-averaged preferential concentration and cluster geometrical statistics as well novel results from time-resolved data on cluster and particle dynamics. We have observed that the time clusters remain coherent exhibits a power-law probability distribution seemingly independent of the three or two-dimensional nature of the data, Stokes number or average concentration within clusters, and that the lifetime of clusters from which particles migrate until disintegration scales with the turnover time of eddies with equivalent volume. Ongoing work focusing on instantaneous concentration rate of change and local particle velocities, conditioned on local concentration, aim to understand the role of enhanced settling on the coherence time-scales of clusters, and to discern between local two-way coupling and gravitational effects on enhanced settling particle velocities. |
Tuesday, November 26, 2024 10:10AM - 10:36AM |
X02.00006: Decoupling between inertial and gravitational effects in the dynamics of particles in turbulence Invited Speaker: Raúl Bayoán B Cal Volcanic ash transport, atmospheric pollution and dust transport are examples of turbulent flows ladened with particles. However, the coupling between several non-dimensional numbers (Rouse, Stokes and Reynolds) provides an entanglement between effects. Decoupling between inertial and gravitational effects in the dynamics of heavy spherical particles in turbulence are experimentally investigated. Several particle-to-fluid density ratios and particle diameters (i.e. different Stokes numbers) are explored in microgravity. When the density of the particle differs from that of the fluid, inertial effects modify the way particles interact with turbulence, e.g., preferential concentration. Being in microgravity conditions allows to experimentally investigate these effects, mitigating possible competition with effects due to gravity (e.g. settling). The experiment is mounted in the Dryden Drop Tower located in Portland State University which provides 2.1 seconds of micro-gravity. Particle tracking velocimetry is performed to access the statistics of the particles. The correlation times between the particles and the flow as well as the Lagrangian statistics will be presented. |
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