Preferential concentration of heavy particles in a turbulent channel flow

Fessler, John R.; Kulick, Jonathan D.; Eaton, John K.

doi:10.1063/1.868445

Cited by 425 publications

(340 citation statements)

References 20 publications

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“…This complicates a study of the extent of clustering. The most commonly used method is 'box counting' (Fessler, Kulick & Eaton 1994). In this method the image is subdivided in smaller regions and a histogram of the number of particles per region is determined.…”

Section: Preferential Concentration Effectsmentioning

confidence: 99%

Particle–fluid interactions in grid-generated turbulence

Poelma¹,

Westerweel²,

Ooms³

2007

J. Fluid Mech.

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The effect of small particles on decaying grid-generated turbulence is studied experimentally. Using a two-camera system, instantaneous fluid-phase and particlephase measurements can be obtained simultaneously. The data obtained with this system are used to study the decay behaviour of the turbulent flow. The role of particle size, particle density and volume load is studied in a number of different cases. These cases are chosen so that the individual role of these parameters can systematically be evaluated. Addition of particles to the flow has significant effects on the decaying turbulence: first, the onset of the turbulent decay appears to shift upstream; second, the flow becomes anisotropic as it develops downstream. The latter is observed as an increase in integral length scale in the vertical direction. The rate at which the flow becomes anisotropic can be predicted using a new parameter: the product of the non-dimensional number density and the Stokes number (referred to as the 'Stokes load'). This parameter, combining the relevant fluid and particle characteristics, is a measure for the energy redistribution leading to anisotropy. In addition to redistributing energy, the particles also produce turbulence. However, this only becomes evident when the grid-generated turbulence has decayed sufficiently, relatively far downstream of the grid. The turbulence production by particles can also account for the observed decrease in slope of the power spectrum, which leads to a 'cross-over' effect. The production of turbulence by the particles can be predicted using a model for the momentum deficit of the particle wakes. The validity of this approach is confirmed using conditional sampling of the fluid velocity field around the particles.

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Section: Preferential Concentration Effectsmentioning

confidence: 99%

Particle–fluid interactions in grid-generated turbulence

Poelma¹,

Westerweel²,

Ooms³

2007

J. Fluid Mech.

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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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“…The number of drops peaks at Q = 0, which represents the region where the magnitude of vorticity rate and strain rate are equal. The number of drops precipitously declines away from Q = 0, and more on the Q > 0 side corresponding to regions of high vorticity than the Q < 0 side corresponding to regions of high strain; this effect has been experimentally observed by Fessler, Kulick & Eaton (1994) and numerically identified in many studies (e.g. Selle & Bellan 2007).…”

Section: The Dynamic Smagorinsky Modelmentioning

confidence: 95%

Explicit filtering to obtain grid-spacing-independent and discretization-order-independent large-eddy simulation of two-phase volumetrically dilute flow with evaporation

Radhakrishnan

Bellan

2013

J. Fluid Mech.

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Predictions from conventional large-eddy simulation (LES) are known to be gridspacing and spatial-discretization-order dependent. In a previous article (Radhakrishnan & Bellan, J. Fluid Mech., vol. 697, 2012a, pp. 399-435), we reformulated LES for compressible single-phase flow by explicitly filtering the nonlinear terms in the governing equations so as to render the solution grid-spacing and discretization-order independent. Having shown in Radhakrishnan & Bellan (2012a) that the reformulated LES, which we call EFLES, yields grid-spacing-independent and discretization-orderindependent solutions for compressible single-phase flow, we explore here the potential of EFLES for evaporating two-phase flow where the small scales have an additional origin compared to single-phase flow. Thus, we created a database through direct numerical simulation (DNS) that when filtered serves as a template for comparisons with both conventional LES and EFLES. Both conventional LES and EFLES are conducted with two gas-phase SGS models; the drop-field SGS model is the same in all these simulations. For EFLES, we also compared simulations performed with the same SGS model for the gas phase but two different drop-field SGS models. Moreover, to elucidate the influence of explicit filtering versus gas-phase SGS modelling, EFLES with two drop-field SGS models but no gas-phase SGS models were conducted. The results from all these simulations were compared to those from DNS and from the filtered DNS (FDNS). Similar to the single-phase flow findings, the conventional LES method yields solutions which are both grid-spacing and spatialdiscretization-order dependent. The EFLES solutions are found to be grid-spacing independent for sufficiently large filter-width to grid-spacing ratio, although for the highest discretization order this ratio is larger in the two-phase flow compared to the single-phase flow. For a sufficiently fine grid, the results are also discretization-order independent. The absence of a gas-phase SGS model leads to build-up of energy near the filter cut-off indicating that while explicit filtering removes energy above the filter width, it does not provide the correct dissipation at the scales smaller than this width. A wider viewpoint leads to the conclusion that although the minimum filter-width to grid-spacing ratio necessary to obtain the unique grid-independent solution might be † Email address for correspondence: josette.bellan@jpl.nasa.govGrid-spacing-independent LES of two-phase flow 231 different for various discretization-order schemes, the grid-independent solution thus obtained is also discretization-order independent.

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Preferential concentration of heavy particles in a turbulent channel flow

Cited by 425 publications

References 20 publications

Particle–fluid interactions in grid-generated turbulence

Particle–fluid interactions in grid-generated turbulence

The dynamics of charged dust in magnetized molecular clouds

Explicit filtering to obtain grid-spacing-independent and discretization-order-independent large-eddy simulation of two-phase volumetrically dilute flow with evaporation

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