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Disks settling in turbulence

Disks settling in turbulence
Disks settling in turbulence
This paper describes an experimental investigation of the dynamics of freely falling thin circular disks settling through turbulence. The patterns of the three dimensional disk motion are studied using an orthogonal arrangement of two high speed cameras. Turbulence is generated in a water tank using a random jet array facility where the jets are mounted in a co-planar configuration. The facility is run continuously until turbulence reaches a statistically stationary state, then, all water pumps are turned off simultaneously and a disk is released after a given waiting time. Contrary to spherical particles, finite-size inertial disks show an increase in the descent velocity for turbulence velocity fluctuations smaller than the particle descent velocity in quiescent flow. Thus, we observe a severe increase of the mean descent velocity of the disk with increasing the magnitude of the turbulence velocity fluctuations (up to $20\%$ of the velocity in quiescent flow for the disk with higher dimensionless inertia $I^*$). We also observe descent events that do not exist for disks falling in still fluid; i.e. `slow tumbling' events and `levitating' events. Finally, we show that the dominant frequency of the particle oscillatory motion decreases for increasing descent velocity and that particles exhibit oscillatory frequencies that never exceed the dominant frequency in quiescent flow in more than $30\%$.
Turbulence, Irregular particles, settling rates, disks
0022-1120
Blay Esteban, Luis
b2b8781e-a741-436f-ba2a-cc475cd10834
Shrimpton, John
9cf82d2e-2f00-4ddf-bd19-9aff443784af
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052
Blay Esteban, Luis
b2b8781e-a741-436f-ba2a-cc475cd10834
Shrimpton, John
9cf82d2e-2f00-4ddf-bd19-9aff443784af
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052

Blay Esteban, Luis, Shrimpton, John and Ganapathisubramani, Bharathram (2020) Disks settling in turbulence. Journal of Fluid Mechanics, 883, [A58]. (doi:10.1017/jfm.2019.922).

Record type: Article

Abstract

This paper describes an experimental investigation of the dynamics of freely falling thin circular disks settling through turbulence. The patterns of the three dimensional disk motion are studied using an orthogonal arrangement of two high speed cameras. Turbulence is generated in a water tank using a random jet array facility where the jets are mounted in a co-planar configuration. The facility is run continuously until turbulence reaches a statistically stationary state, then, all water pumps are turned off simultaneously and a disk is released after a given waiting time. Contrary to spherical particles, finite-size inertial disks show an increase in the descent velocity for turbulence velocity fluctuations smaller than the particle descent velocity in quiescent flow. Thus, we observe a severe increase of the mean descent velocity of the disk with increasing the magnitude of the turbulence velocity fluctuations (up to $20\%$ of the velocity in quiescent flow for the disk with higher dimensionless inertia $I^*$). We also observe descent events that do not exist for disks falling in still fluid; i.e. `slow tumbling' events and `levitating' events. Finally, we show that the dominant frequency of the particle oscillatory motion decreases for increasing descent velocity and that particles exhibit oscillatory frequencies that never exceed the dominant frequency in quiescent flow in more than $30\%$.

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Accepted/In Press date: 31 October 2019
e-pub ahead of print date: 2 December 2019
Published date: 25 January 2020
Keywords: Turbulence, Irregular particles, settling rates, disks

Identifiers

Local EPrints ID: 435851
URI: http://eprints.soton.ac.uk/id/eprint/435851
ISSN: 0022-1120
PURE UUID: f54b9ae8-aecb-4bed-8fe3-80cf5ad46145
ORCID for Bharathram Ganapathisubramani: ORCID iD orcid.org/0000-0001-9817-0486

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Date deposited: 21 Nov 2019 17:30
Last modified: 07 Oct 2020 01:58

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