Effects of particle size and background rotation on the settling of particle clouds

Kriaa, Quentin; Subra, Eliot; Favier, Benjamin; Bars, Michaël Le

doi:10.1103/physrevfluids.7.124302

Cited by 8 publications

(3 citation statements)

References 48 publications

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“…They are dominated by highly transient interactions between the particles and the fluid, especially at the interface between cloud and vacant fluid. Vortex rings at the cloud front entrain the surrounding fluid and deform the shape of the cloud [12][13][14]. These systems are of interest as the dependence of their behavior on the particle properties can be used to, for instance, determine the particle size distribution [13,15].…”

Section: Introductionmentioning

confidence: 99%

Settling of localized particle plumes in a quiescent water tank

Zürner

Toupoint²,

Souza³

et al. 2023

Phys. Rev. Fluids

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The fall or rise of inertial particles plumes in an initially quiescent fluid is ubiquitous in natural and industrial processes. Disentangling the influence of the numerous parameters of these systems on the plume velocity is thus a major issue. Moreover, understanding the energy transfer between the two phases and the structure of induced flow is another very relevant question. A specific experiment has been designed to tackle these problems. A continuous plume of inertial particles released above the center of a still water tank generates a large-scale recirculation flow. The present experimental study investigates the stationary settling dynamics and induced flow properties using various particle populations with particle-to-fluid density ratios from 3.8 to 14.3, Archimedes numbers 4 to 580 and mass fractions 10 −6 to 10 −3 , revealing an unexplored region of the parameter space. The fluid and particle velocities are measured simultaneously by two cameras, utilizing optical filtering and image post-processing. It is found that the settling in the laboratory frame generally follows the terminal velocity predicted using the Schiller-Naumann drag. The particle velocity relative to the surrounding fluid is unaffected by the particle mass fraction and always hindered due to the kinetic energy transferred to the fluid. This transfer of energy is most effective for low Archimedes numbers. All modifications of the settling behavior due to the particle mass fraction are caused by the back-reaction of the induced flow on the particles, no direct particle-particle interactions are observed.

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Section: Introductionmentioning

confidence: 99%

Settling of localized particle plumes in a quiescent water tank

Zürner

Toupoint²,

Souza³

et al. 2023

Phys. Rev. Fluids

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“…A more general model allowing, for example, thermodynamic disequilibrium would require parameterization of all small‐scale effects, which are still poorly understood (Loper, 1992). In addition, the interaction between reactive particles (Huguet et al., 2020) and a stratified layer, as well as the collective behavior of iron crystals (Kriaa et al., 2022) and their effects on large‐scale flow, can alter the picture of steady iron snow. While the heterogeneity of the flux at the core upper boundary (Amit et al., 2015) or the radial distribution of the buoyancy flux (Cao et al., 2014) modify the resulting magnetic field, dynamo simulations driven by iron snow have so far assumed a uniform and stationary buoyancy flux below the snow layer (Christensen, 2015; Vilim et al., 2010).…”

Section: Introductionmentioning

confidence: 99%

A Laboratory Model for Iron Snow in Planetary Cores

Huguet,

Le Bars,

Deguen

2023

Geophysical Research Letters

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Solidification of the cores of small planets and moons is thought to occur in the “iron snow” regime, in which iron crystals form near the core‐mantle boundary and fall until re‐melting at greater depth. The resulting buoyancy flux may sustain convection and dynamo action. This regime of crystallization is poorly understood. Here we present the first laboratory experiments designed to model iron snow. We find that solidification happens in a cyclic pattern, with intense solidification bursts separated by crystal‐free periods. This is explained by the necessity of reaching a finite amount of supercooling to re‐initiate crystallization once the crystals formed earlier have migrated away. When scaled to planetary cores, our results suggest that crystallization and the associated buoyancy flux would be strongly heterogeneous in time and space, which eventually impacts the time variability and geometry of the magnetic field.

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“…Dávila & Hunt (2001) and Ghosh et al describe the quantification of drift integrals (essentially the added length scale a falling particle must negotiate to settle past a microscale eddy) 24,25 . Contemporary research continues to use these calculations applying them to diverse fluid mechanical applications 26 and a review can be found from Shaw 27 . However, this new mechanism required supporting experimental data in the form of fast response in situ data to study how interparticle distances are modulated by such droplet-vortical interactions.…”

mentioning

confidence: 99%

Turbulence-induced droplet grouping and augmented rain formation in cumulus clouds

Gumber,

Bera,

Ghosh

et al. 2024

Sci Rep

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This paper provides the first observational analysis of how droplet separation is impacted by the flinging action of microscale vortices in turbulent clouds over a select radii range and how they vary over cloud cores and along the peripheral edges. It is premised that this mechanism initiates droplet separation within a cloud volume soon after condensational growth, largely in the cloud core, and operates until the cloud droplet radii exceed 20–30 µm when this effect fades rapidly. New observations are presented showing how microscale vortices also impact the settling rates of droplets over a critical size range (6–18 µm) causing them to sediment faster than in still air affecting swept volumes and thereby impacting the rain initiation and formation. Large-scale atmospheric models ignore these microscale effects linked to rapid droplet growth during the early stages of cloud conversion. Previous studies on droplet spatial organization along the cloud edges and inside the deep core have shown that homogeneous Poisson statistics, indicative of the presence of a vigorous in-cloud mixing process at small scales obtained, in contrast to an inhomogeneous distribution along the edges. In this paper, it is established that this marked core region, homogeneity can be linked to microscale vortical activity which flings cloud droplets in the range of 6–18 µm outward. The typical radius of the droplet trajectories or the droplet flung radii around the vortices correlates with the interparticle distance strongly. The correlation starts to diminish as one proceeds from the central core to the cloud fringes because of the added entrainment of cloud-free air. These first results imply that droplet growth in the core is first augmented with this small-scale interaction prior to other more large-scale processes involving entrainment mixing. This first study, combining these amplified velocities are included in a Weather Research and Forecasting- LES case study. Not only are significant differences observed in the cloud morphology when compared to a baseline case, but the ‘enhanced’ case also shows early commencement of rainfall along with intense precipitation activity compared to the ‘standard’ baseline case. It is also shown that the modelled equilibrium raindrop spectrum agrees better with observations when the enhanced droplet sedimentation rates mediated by microscale vortices are included in the calculations compared to the case where only still-air terminal velocities are used.

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Effects of particle size and background rotation on the settling of particle clouds

Cited by 8 publications

References 48 publications

Settling of localized particle plumes in a quiescent water tank

Settling of localized particle plumes in a quiescent water tank

A Laboratory Model for Iron Snow in Planetary Cores

Turbulence-induced droplet grouping and augmented rain formation in cumulus clouds

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