Settling behaviour of thin curved particles in quiescent fluid and turbulence

Chan, Timothy T. K.; Esteban, Luis Blay; Huisman, Sander G.; Shrimpton, John S.; Ganapathisubramani, Bharathram

doi:10.1017/jfm.2021.520

J. Fluid Mech.

2021

DOI: 10.1017/jfm.2021.520

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Settling behaviour of thin curved particles in quiescent fluid and turbulence

Timothy T. K. Chan

Luis Blay Esteban

Sander G. Huisman

et al.

Abstract: Abstract

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2024

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Cited by 4 publications

References 51 publications

(144 reference statements)

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Structure and energy transfer in homogeneous turbulence below a free surface

Ruth,

Coletti

2024

J. Fluid Mech.

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We investigate the turbulence below a quasi-flat free surface, focusing on the energy transport in space and across scales. We leverage a large zero-mean-flow tank where homogeneous turbulence is generated by randomly actuated jets. A wide range of Reynolds number is spanned, reaching sufficient scale separation for the emergence of an inertial sub-range. Unlike previous studies, the forcing extends through the source layer, although the surface deformation remains millimetric. Particle image velocimetry along a surface-normal plane resolves from the dissipative to the integral scales. The contributions to turbulent kinetic energy from both vertical and horizontal components of velocity approach the prediction based on rapid distortion theory as the Reynolds number is increased, indicating that discrepancies among previous studies are likely due to differences in the forcing. At odds with the theory, however, the integral scale of the horizontal fluctuations grows as the surface is approached. This is rooted in the profound influence exerted by the surface on the inter-scale energy transfer: along horizontal separations, the direct cascade of energy in horizontal fluctuations is hindered, while an inverse cascade of that in vertical fluctuations is established. This is connected to the structure of upwellings and downwellings. The former, characterized by somewhat larger spatial extent and stronger intensity, are associated with extensional surface-parallel motions. They thus transfer energy to the larger horizontal scales, prevailing over downwellings which favour the compression (and concurrent vertical stretching) of the eddies. Both types of structures extend to depths between the integral scale and the Taylor microscale.

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Structure and energy transfer in homogeneous turbulence below a free surface

Ruth,

Coletti

2024

J. Fluid Mech.

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On the dynamics and wakes of a freely settling Platonic polyhedron in a quiescent Newtonian fluid

Gai,

Wachs

2024

J. Fluid Mech.

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We investigate systematically the free settling of a single Platonic polyhedron in an unbounded domain filled with an otherwise quiescent Newtonian fluid. We consider a particle–fluid density mimicking a rock in water. Five Platonic polyhedrons of increasing sphericity are studied for a range of Galileo numbers $10 \leqslant \mathcal {G}a \leqslant 300$ . We construct a regime map in the parameter space of Galileo number and particle volume fraction ( $\mathcal {G}a, \phi$ ), highlighting how the angularity of the Platonic polyhedron impacts its settling path and the onset of instabilities. We find that the initial angular position solely affects the transient settling process. All the Platonic polyhedrons maintain a stable settling angular position at low $\mathcal {G}a$ . Higher angularity leads to path unsteadiness at lower $\mathcal {G}a$ . Path instability progresses from steady vertical to unsteady vertical, followed by oblique settling observed for highly spherical particles, but helical settling (HS) for more angular particles. The particle autorotation is found to be the pivotal factor influencing path instability and the regime transition of angular particles. Beginning in the unsteady oblique and helical regimes, particle autorotation becomes more prevalent, escalating further in the chaotic regime as $\mathcal {G}a$ increases. The particle angular velocity vector is shown to be predominantly situated in the horizontal plane. A thorough force balance in the horizontal plane reveals that the Magnus force is the primary driving force of the HS regime. Additionally, we establish two new empirical correlations to predict the particle settling velocity and the disturbed wake length that solely require the physical properties of the system ( $\mathcal {G}a$ and $\phi$ ). Our numerical results suggest that an increase of the density ratio from $2$ to $3$ exerts only a marginal impact on the path instability of the most angular particle, the settling tetrahedron.

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A quasi-two-dimensional fluid experimental apparatus based on tank-in-tank configuration

Chen

Sun

Tian

et al. 2023

Review of Scientific Instruments

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The fluid tank is an essential facility for experimental research on fluid mechanics. However, owing to the hydrostatic fluid pressure, a fine uniformity of the narrow channel is difficult to be maintained in a tall narrow–channel tank. To address this issue, we proposed a quasi-two-dimensional fluid experimental apparatus based on a “tank-in-tank” configuration and built with an outer tank and an inner tank. The outer tank was cuboid-shaped and used to load the fluid medium, while the inner tank, consisting of two parallel glass plates, was embedded into the outer tank and served as the experimental channel. The hydrostatic pressure acting on the channel was balanced so that a high level of uniformity was maintained over the whole channel. The available height and width of the channel were 2800 and 1500 mm, respectively, while its gap distance could be adaptive from 0 to 120 mm. Experimental research on motion characteristics of circular disks falling in the quasi-2D channel was implemented to investigate the effects of the falling environment and disk geometry. Four distinct falling types were observed, and the wake flow fields of the falling disks were visualized. The Reynolds numbers of falling disks ranged from 400 to 63 000 presently. Chaotic motion and regular motion were demarcated at Re ≈ 30 000. An analytical model was established to predict the final average falling velocity and Reynolds number. Finally, potential directions for future research and improvements to the apparatus were suggested.

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Settling behaviour of thin curved particles in quiescent fluid and turbulence

Abstract: Abstract

Cited by 4 publications

References 51 publications

Structure and energy transfer in homogeneous turbulence below a free surface

Structure and energy transfer in homogeneous turbulence below a free surface

On the dynamics and wakes of a freely settling Platonic polyhedron in a quiescent Newtonian fluid

A quasi-two-dimensional fluid experimental apparatus based on tank-in-tank configuration

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