A falling cloud of particles at a small but finite Reynolds number

Pignatel, Florent; Nicolas, Maxime; Guazzelli, Élisabeth

doi:10.1017/s0022112010005501

Cited by 48 publications

(26 citation statements)

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“…As the viscosity of the fluid for Re = 0.05 is much larger than the viscosity for Re = 50, columns at large Re in the absolute frame will experience a faster dynamics. These results are qualitatively comparable to those of Pignatel et al [6], which showed that increasing Re enhances effective cohesion and slows the falling of spherical clouds of particles. Figure 2 shows the time variation of the center of mass V mass reduced by a corrected characteristic velocity of the column U cyl .…”

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confidence: 91%

“…Therefore, many investigations were done in order to better understand the behavior of these particle-laden flows, presenting a large panel of geometries such as jets, streams, drops, and spherical clouds. The sedimentation of spherical clouds of particles, in an external fluid of variable viscosity, has been recently investigated experimentally and numerically [6]. With the exception of the experimental work of Nicolas [7], investigations related to jets or column of particles focused mainly on highly viscous fluids (i.e., zero Reynolds numbers limit) [8,9], air, and moderate vacuum (large Reynolds numbers limit) [10][11][12] or other kinds of interactions: capillary bridges, van der Waals forces [13-16], etc.…”

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confidence: 99%

“…At the beginning of the simulation, we randomly initialize the positions of N 0 particles in a cylindrical column of radius R 0 and length H 0 ; the dimensionless particle density n 0 = N 0 /π h * is homogeneous (h * = H 0 /R 0 ). In addition to their settling velocity U η = F /6πηa in the fluid of viscosity η under the action of the gravitational force F , the point particles of radius a are subject to the hydrodynamic pairwise interactions modeled by the dimensionless Green's function of the Oseen equation [2,3,6], which represents the additional velocity induced on a point particle by another point-particle distant by d = (d x ,d y ,d z ):In Eq.(1), all lengths and velocities were made dimensionless using U η as a reference velocity and R 0 as a reference length. A reference time τ η = R 0 /U η was also defined.…”

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Sedimentation of granular columns in the viscous and weakly inertial regimes

Chraïbi

Amarouchène

2013

Phys. Rev. E

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We investigate the dynamics of granular columns of point particles that interact via long-range hydrodynamic interactions and fall under the action of gravity. We investigate the influence of inertia using the Green's function for the Oseen equation. The initial conditions (density and aspect ratio) are systematically varied. Our results suggest that universal self-similar laws may be sufficient to characterize the temporal and structural evolution of the granular columns. A characteristic time above which an instability is triggered (which may enable the formation of clusters) is also retrieved and discussed.

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confidence: 99%

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confidence: 99%

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Sedimentation of granular columns in the viscous and weakly inertial regimes

Chraïbi

Amarouchène

2013

Phys. Rev. E

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“…A “cloud” is defined as a very larger number of particles surrounded by clear fluid [112,113,114,115,116,117,118,119,120,121,122,123,124,125,126]. A cloud of droplets can be treated as a single droplet ( i.e.…”

Section: Studies Of Toxic Aerosols From Inhaled Cigarette Smokementioning

confidence: 99%

Lung Deposition Analyses of Inhaled Toxic Aerosols in Conventional and Less Harmful Cigarette Smoke: A Review

Kleinstreuer

Feng

2013

IJERPH

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Inhaled toxic aerosols of conventional cigarette smoke may impact not only the health of smokers, but also those exposed to second-stream smoke, especially children. Thus, less harmful cigarettes (LHCs), also called potential reduced exposure products (PREPs), or modified risk tobacco products (MRTP) have been designed by tobacco manufacturers to focus on the reduction of the concentration of carcinogenic components and toxicants in tobacco. However, some studies have pointed out that the new cigarette products may be actually more harmful than the conventional ones due to variations in puffing or post-puffing behavior, different physical and chemical characteristics of inhaled toxic aerosols, and longer exposure conditions. In order to understand the toxicological impact of tobacco smoke, it is essential for scientists, engineers and manufacturers to develop experiments, clinical investigations, and predictive numerical models for tracking the intake and deposition of toxicants of both LHCs and conventional cigarettes. Furthermore, to link inhaled toxicants to lung and other diseases, it is necessary to determine the physical mechanisms and parameters that have significant impacts on droplet/vapor transport and deposition. Complex mechanisms include droplet coagulation, hygroscopic growth, condensation and evaporation, vapor formation and changes in composition. Of interest are also different puffing behavior, smoke inlet conditions, subject geometries, and mass transfer of deposited material into systemic regions. This review article is intended to serve as an overview of contributions mainly published between 2009 and 2013, focusing on the potential health risks of toxicants in cigarette smoke, progress made in different approaches of impact analyses for inhaled toxic aerosols, as well as challenges and future directions.

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“…Among the various intriguing phenomena they observed is the well-known cascade of falling plumes, which often occur during the descent of heavy drops [2][3][4]. Similar Rayleigh-Taylor-type instabilities also arise for heavy suspension droplets [2,5,6]. Heavy particles inside the drop can lead to formation of a Hill-type vortex, with a toroidal structure which can become destabilized to form localized plumes.…”

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confidence: 99%

Vortex-induced buckling of a viscous drop impacting a pool

Beilharz

Thoroddsen

2017

Phys. Rev. Fluids

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CitationLi EQ, Beilharz D, Thoroddsen ST (2017) We study the intricate buckling patterns which can form when a viscous drop impacts a much lower viscosity miscible pool. The drop enters the pool by its impact inertia, flattens, and sinks by its own weight while stretching into a hemispheric bowl. Upward motion along the outer bottom surface of this bowl produces a vortical boundary layer which separates along its top and rolls up into a vortex ring. The vorticity is therefore produced in a fundamentally different way than for a drop impacting a pool of the same liquid. The vortex ring subsequently advects into the bowl, thereby stretching the drop liquid into ever thinner sheets, reaching the micron level. The rotating motion around the vortex pulls in folds to form multiple windings of double-walled toroidal viscous sheets. The axisymmetric velocity field thereby stretches the drop liquid into progressively finer sheets, which are susceptible to both axial and azimuthal compression-induced buckling. The azimuthal buckling of the sheets tends to occur on the inner side of the vortex ring, while their folds can be stretched and straightened on the outside edge. We characterize the total stretching from high-speed video imaging and use particle image velocimetry to track the formation and evolution of the vortex ring. The total interfacial area between the drop and the pool liquid can grow over 40-fold during the first 50 ms after impact. Increasing pool viscosity shows entrapment of a large bubble on top of the drop, while lowering the drop viscosity produces intricate buckled shapes, appearing at the earliest stage and being promoted by the crater motions. We also present an image collage of the most intriguing and convoluted structures observed. Finally, a simple point-vortex model reproduces some features from the experiments and shows variable stretching along the wrapping sheets.

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A falling cloud of particles at a small but finite Reynolds number

Cited by 48 publications

References 11 publications

Sedimentation of granular columns in the viscous and weakly inertial regimes

Sedimentation of granular columns in the viscous and weakly inertial regimes

Lung Deposition Analyses of Inhaled Toxic Aerosols in Conventional and Less Harmful Cigarette Smoke: A Review

Vortex-induced buckling of a viscous drop impacting a pool

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