Preferential concentration of heavy particles: A Voronoï analysis

Monchaux, Romain; Bourgoin, Mickaël; Cartellier, Alain H.

doi:10.1063/1.3489987

Cited by 272 publications

(435 citation statements)

References 22 publications

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“…comm., 2011). By analysing Voronoi diagrams of wind tunnel data, Monchaux et al (2010) also find that clustering peaks at St ∼ 1. Both DNS and experiment show that the RDF approaches a plateau at small separations and the exponent of the bidisperse RDF approaches that of the equivalent monodisperse RDF for the particle with the smaller Stokes number.…”

Section: Laboratory Experimentsmentioning

confidence: 99%

Droplet growth in warm turbulent clouds

Devenish

Bartello

Brenguier

et al. 2012

Quart J Royal Meteoro Soc

245

281

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In this survey we consider the impact of turbulence on cloud formation from the cloud scale to the droplet scale. We assess progress in understanding the effect of turbulence on the condensational and collisional growth of droplets and the effect of entrainment and mixing on the droplet spectrum. The increasing power of computers and better experimental and observational techniques allow for a much more detailed study of these processes than was hitherto possible. However, much of the research necessarily remains idealized and we argue that it is those studies which include such fundamental characteristics of clouds as droplet sedimentation and latent heating that are most relevant to clouds. Nevertheless, the large body of research over the last decade is beginning to allow tentative conclusions to be made. For example, it is unlikely that small-scale turbulent eddies (i.e. not the energy-containing eddies) alone are responsible for broadening the droplet size spectrum during the initial stage of droplet growth due to condensation. It is likely, though, that small-scale turbulence plays a significant role in the growth of droplets through collisions and coalescence. Moreover, it has been possible through detailed numerical simulations to assess the relative importance of different processes to the turbulent collision kernel and how this varies in the parameter space that is important to clouds. The focus of research on the role of turbulence in condensational and collisional growth has tended to ignore the effect of entrainment and mixing and it is arguable that they play at least as important a role in the evolution of the droplet spectrum. We consider the role of turbulence in the mixing of dry and cloudy air, methods of quantifying this mixing and the effect that it has on the droplet spectrum. Copyright

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Section: Laboratory Experimentsmentioning

confidence: 99%

Droplet growth in warm turbulent clouds

Devenish

Bartello

Brenguier

et al. 2012

Quart J Royal Meteoro Soc

245

281

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“…Bracco et al 1999;Cuzzi et al 2001;Youdin & Goodman 2005;Johansen & Youdin 2007;Carballido et al 2008;Bai & Stone 2010a,b;Pan et al 2011;Dittrich et al 2013;Jalali 2013;Hopkins 2014a). Large fluctuations in the density of aerodynamic particles relative to gas have also long been observed in terrestrial turbulence (Squires & Eaton 1991;Fessler et al 1994;Rouson & Eaton 2001;Gualtieri et al 2009;Monchaux et al 2010). …”

Section: Introductionmentioning

confidence: 99%

The dynamics of charged dust in magnetized molecular clouds

Lee

Hopkins

Squire

2017

Monthly Notices of the Royal Astronomical Society

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We study the dynamics of large, charged dust grains in turbulent giant molecular clouds (GMCs). Massive dust grains behave as aerodynamic particles in primarily neutral dense gas, and thus are able to produce dramatic small-scale fluctuations in the dust-to-gas ratio. Hopkins & Lee (2016) directly simulated the dynamics of neutral dust grains in super-sonic MHD turbulence, typical of GMCs, and showed that the dust-to-gas fluctuations can exceed factor ∼ 1000 on small scales, with important implications for star formation, stellar abundances, and dust behavior and growth. However, even in primarily neutral gas in GMCs, dust grains are negatively charged and Lorentz forces are non-negligible. Therefore, we extend our previous study by including the effects of Lorentz forces on charged grains (in addition to drag). For small charged grains (sizes 0.1 µm), Lorentz forces suppress dust-to-gas ratio fluctuations, while for large grains (sizes 1 µm), Lorentz forces have essentially no effect, trends that are well explained with a simple theory of dust magnetization. In some special intermediate cases, Lorentz forces can enhance dust-gas segregation. Regardless, for the physically expected scaling of dust charge with grain size, we find the most important effects depend on grain size (via the drag equation) with Lorentz forces/charge as a second-order correction. We show that the dynamics we consider are determined by three dimensionless numbers in the limit of weak background magnetic fields: the turbulent Mach number, a dust drag parameter (proportional to grain size) and a dust Lorentz parameter (proportional to grain charge); these allow us to generalize our simulations to a wide range of conditions.

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“…One has to define the threshold above which the concentration is high. To this end, following Monchaux et al (2010Monchaux et al ( , 2012, we compare the probability density function of the logarithm of the Voronoï cell volume, P(v), obtained from the set of particles to be analysed with the semi-analytic distribution corresponding to a random homogeneous particle distribution P r (v) (Ferenc & Néda 2007). The two curves present two intersections at v c and v v : P(v c ) = P r (v c ) and…”

Section: A1 Reference Statementioning

confidence: 99%

“…Like many authors (Monchaux et al 2010;Garcia-Villalba, Kidanemariam & Uhlmann 2012;Monchaux, Bourgoin & Cartellier 2012;Tagawa et al 2012Tagawa et al , 2013Dejoan & Monchaux 2013;Nicolai, Jacob & Piva 2013;Nilsen, Andersson & Zhao 2013;Uhlmann & Doychev 2014), we base our analysis of the particle clustering on Voronoï tessellation of the particle positions. Each of the elementary cells of the Voronoï tessellation is attributed to a particle.…”

Section: A1 Reference Statementioning

confidence: 99%

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Turbulent thermal convection driven by heated inertial particles

et al. 2016

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This is an author-deposited version published in: http://oatao.univ-toulouse.fr/ Eprints ID: 18470Open Archive Toulouse Archive Ouverte (OATAO) OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. The heating of particles in a dilute suspension, for instance by radiation, chemical reactions or radioactivity, leads to local temperature fluctuations in the fluid due to the non-uniformity of the disperse phase. In the presence of a gravity field, the fluid is set in motion by the resulting buoyancy forces. When the particle density is different than that of the fluid, the fluid motion alters the spatial distribution of the particles and possibly strengthens their concentration inhomogeneities. This in turn causes more intense local heating. Direct numerical simulations in the Boussinesq limit show this feedback loop. Various regimes are identified depending on the particle inertia. For very small particle inertia, the macroscopic behaviour of the system is the result of many thermal plumes that are generated independently of each other. For significant particle inertia, clusters of particles are observed and their dynamics controls the flow. The emergence of very intermittent turbulent fluctuations shows that the flow is influenced by the larger structures (turbulent convection) as well as by the small-scale dynamics that affect particle segregation and thus the flow forcing. Assuming thermal equilibrium between the particles and the fluid (i.e. infinitely fast thermal relaxation of the particle), we investigate the evolution of statistical observables with the change of the main control parameters (namely the particle number density, the particle inertia and the domain size), and propose a scaling argument for these trends. Concerning the energy density in the spectral space, it is observed that the turbulent energy and temperature spectra follow a power law, the exponent of which varies continuously with the Stokes number. Furthermore, the study of the spectra of the temperature and momentum forcing (and thus of the concentration/temperature and velocity/temperature correlations) gives strong support to the proposed feedback loop mechanism. We then discuss the intermittency of the flow, and analyse the effect of relaxing some of the simplifying assumptions, thus assessing the relevance of the original studied configuration. To cite this version:

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Preferential concentration of heavy particles: A Voronoï analysis

Cited by 272 publications

References 22 publications

Droplet growth in warm turbulent clouds

Droplet growth in warm turbulent clouds

The dynamics of charged dust in magnetized molecular clouds

Turbulent thermal convection driven by heated inertial particles

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