Where do small, weakly inertial particles go in a turbulent flow?

Gibert, Mathieu; Xu, Haitao; Bodenschatz, Eberhard

doi:10.1017/jfm.2012.72

Cited by 45 publications

(41 citation statements)

References 33 publications

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“…In homogeneous turbulence the mechanism of preferential concentration causes the inertial particles to be in regions of low enstrophy and high strain (Squires & Eaton 1991;Gibert et al 2012). This is confirmed also for the considered flow in figure 8, that displays the joint PDF of normalized particle concentration C/C o and fluid enstrophy ξ /ξ o , where ξ is the fluid enstrophy.…”

Section: Particle Distributionsupporting

confidence: 68%

“…Particles of St η = 1 also display maximum dispersion rates and maximum time rate of change of their temperature fluctuations (Wetchagarun & Riley 2010). In the last decade, experimental, numerical and theoretical studies have deepened our understanding of the origins of turbulence clustering (Goto & Vassilicos 2008;Salazar et al 2008;Gibert, Xu & Bodenschatz 2012;Bragg & Collins 2014), its consequences on the statistics of particle motion (Ayyalasomayajula et al 2006;Bec et al 2006) and on the particle collision rate (Sundaram & Collins 1997;Wang, Wexler & Zhou 2000).…”

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confidence: 99%

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Settling of heated particles in homogeneous turbulence

Frankel

Pouransari

Coletti³

et al. 2016

J. Fluid Mech.

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We study the case of inertial particles heated by thermal radiation while settling by gravity through a turbulent transparent gas. We consider dilute and optically thin regimes in which each particle receives the same heat flux. Numerical simulations of forced homogeneous turbulence are performed taking into account the two-way coupling of both momentum and temperature between the dispersed and continuous phases. Particles much smaller than the smallest flow scales are considered and the point-particle approximation is adopted. The particle Stokes number (based on the Kolmogorov time scale) is of order unity, while the nominal settling velocity is up to an order of magnitude larger than the Kolmogorov velocity, marking a critical difference with previous two-way coupled simulations. It is found that non-heated particles enhance turbulence when their settling velocity is sufficiently high compared to the Kolmogorov velocity. Energy spectra show that the non-heated particle settling impacts both the very small and very large flow scales, while the intermediate scales are weakly affected. When heated, particles shed plumes of buoyant gas, further modifying the turbulence structure. At the considered radiation intensities, clustering is strong but the classic mechanism of preferential concentration is modified, while preferential sweeping is eliminated or even reversed. Particle heating also causes a significant reduction of the mean settling velocity, which is caused by rising buoyant plumes in the vicinity of particle clusters. The turbulent kinetic energy is affected non-monotonically as the radiation intensity is increased due to the competing effects of the downward gravitational force and the upward buoyancy force. The thermal radiation influences all scales of the turbulence. The effects of settling and buoyancy on the turbulence anisotropy are also discussed.

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Section: Particle Distributionsupporting

confidence: 68%

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confidence: 99%

Settling of heated particles in homogeneous turbulence

Frankel

Pouransari

Coletti³

et al. 2016

J. Fluid Mech.

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“…Specifically, techniques for Lagrangian tracking of particles in turbulent flows have provided new perspectives on the behavior of inertial particles in turbulence (Ayyalasomayajula et al, 2006;Gibert et al, 2012;Bewley et al, 2013). Of course, there are deviations from idealized flow conditions achievable in a laboratory setting: for example, boundary conditions vary in time so that quasi-stationary conditions must be sought.…”

Section: Discussionmentioning

confidence: 99%

High-resolution measurement of cloud microphysics and turbulence at a mountaintop station

et al. 2015

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Abstract. Mountain research stations are advantageous not only for long-term sampling of cloud properties but also for measurements that are prohibitively difficult to perform on airborne platforms due to the large true air speed or adverse factors such as weight and complexity of the equipment necessary. Some cloud-turbulence measurements, especially Lagrangian in nature, fall into this category. We report results from simultaneous, high-resolution and collocated measurements of cloud microphysical and turbulence properties during several warm cloud events at the Umweltforschungsstation Schneefernerhaus (UFS) on Zugspitze in the German Alps. The data gathered were found to be representative of observations made with similar instrumentation in free clouds. The observed turbulence shared all features known for high-Reynolds-number flows: it exhibited approximately Gaussian fluctuations for all three velocity components, a clearly defined inertial subrange following Kolmogorov scaling (power spectrum, and second-and thirdorder Eulerian structure functions), and highly intermittent velocity gradients, as well as approximately lognormal kinetic energy dissipation rates. The clouds were observed to have liquid water contents on the order of 1 g m −3 and size distributions typical of continental clouds, sometimes exhibiting long positive tails indicative of large drop production through turbulent mixing or coalescence growth. Dimensionless parameters relevant to cloud-turbulence interactions, the Stokes number and settling parameter are in the range typically observed in atmospheric clouds. Observed fluctuations in droplet number concentration and diameter suggest a preference for inhomogeneous mixing. Finally, enhanced variance in liquid water content fluctuations is observed at high frequencies, and the scale break occurs at a value consistent with the independently estimated phase relaxation time from microphysical measurements.

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“…The range of turbulence intensities over which these small animals remain able to perform some of the striking behavioural features that they display in still water, for instance trail-following behaviour, is also worth exploring. In a turbulent flow, particles with small to moderate inertia and size below or equal to the Kolmogorov length scale tend to move preferentially to regions of low vorticity and high strain [81]. Because in these regions peak density of particles can be much higher than the mean value [82], it was suggested that preferential concentrations can increase copepod encounter rates in the ocean [62].…”

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confidence: 99%

Turbulence triggers vigorous swimming but hinders motion strategy in planktonic copepods

Michalec

Souissi

Holzner

2015

J. R. Soc. Interface.

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Calanoid copepods represent a major component of the plankton community. These small animals reside in constantly flowing environments. Given the fundamental role of behaviour in their ecology, it is especially relevant to know how copepods perform in turbulent flows. By means of three-dimensional particle tracking velocimetry, we reconstructed the trajectories of hundreds of adult Eurytemora affinis swimming freely under realistic intensities of homogeneous turbulence. We demonstrate that swimming contributes substantially to the dynamics of copepods even when turbulence is significant. We show that the contribution of behaviour to the overall dynamics gradually reduces with turbulence intensity but regains significance at moderate intensity, allowing copepods to maintain a certain velocity relative to the flow. These results suggest that E. affinis has evolved an adaptive behavioural mechanism to retain swimming efficiency in turbulent flows. They suggest the ability of some copepods to respond to the hydrodynamic features of the surrounding flow. Such ability may improve survival and mating performance in complex and dynamic environments. However, moderate levels of turbulence cancelled gender-specific differences in the degree of space occupation and innate movement strategies. Our results suggest that the broadly accepted mate-searching strategies based on trajectory complexity and movement patterns are inefficient in energetic environments.

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Where do small, weakly inertial particles go in a turbulent flow?

Cited by 45 publications

References 33 publications

Settling of heated particles in homogeneous turbulence

Settling of heated particles in homogeneous turbulence

High-resolution measurement of cloud microphysics and turbulence at a mountaintop station

Turbulence triggers vigorous swimming but hinders motion strategy in planktonic copepods

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