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Disks settling in turbulence

Published online by Cambridge University Press:  02 December 2019

L. B. Esteban Open the ORCID record for L. B. Esteban [Opens in a new window] ,
J. S. Shrimpton  and
B. Ganapathisubramani
L. B. Esteban*
Affiliation:
Aerodynamics and Flight Mechanics Group, University of Southampton, University Rd, SouthamptonSO17 1BJ, UK
J. S. Shrimpton
Affiliation:
Aerodynamics and Flight Mechanics Group, University of Southampton, University Rd, SouthamptonSO17 1BJ, UK
B. Ganapathisubramani
Affiliation:
Aerodynamics and Flight Mechanics Group, University of Southampton, University Rd, SouthamptonSO17 1BJ, UK
*
†Email address for correspondence: L.Blay-Esteban@soton.ac.uk
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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 magnitude of the turbulence velocity fluctuations (up to $20\,\%$ of the velocity in quiescent flow for the disk with higher dimensionless inertia $I^{\ast }$). 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 by more than $30\,\%$.

JFM classification

Turbulent Flows: Homogeneous turbulence Multiphase and Particle-laden Flows: Multiphase flow
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 883 , 25 January 2020 , A58
Copyright
© 2019 Cambridge University Press

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