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Settling regimes of inertial particles in isotropic turbulence

Published online by Cambridge University Press:  28 October 2014

G. H. Good*
Affiliation:
Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA Max Planck Institute for Dynamics and Self-Organization, 37077 Göttingen, Germany International Collaboration for Turbulence Research
P. J. Ireland
Affiliation:
Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA International Collaboration for Turbulence Research
G. P. Bewley
Affiliation:
Max Planck Institute for Dynamics and Self-Organization, 37077 Göttingen, Germany International Collaboration for Turbulence Research
E. Bodenschatz
Affiliation:
Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA Max Planck Institute for Dynamics and Self-Organization, 37077 Göttingen, Germany International Collaboration for Turbulence Research
L. R. Collins
Affiliation:
Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA International Collaboration for Turbulence Research
Z. Warhaft
Affiliation:
Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA Atkinson Center for a Sustainable Future, Cornell University, Ithaca, NY 14853, USA International Collaboration for Turbulence Research
*
Email address for correspondence: ghg36@cornell.edu

Abstract

We investigate the settling speeds and root mean square (r.m.s.) velocities of inertial particles in isotropic turbulence with gravity using experiments with water droplets in air turbulence from 32 loudspeaker jets and direct numerical simulations (DNS). The dependence on particle inertia, gravity and the scales of both the smallest and largest turbulent eddies is investigated. We isolate the mechanisms of turbulence settling modification and find that the reduced settling speeds of large particles in experiments are due to nonlinear drag effects. We demonstrate using DNS that reduced settling speeds with linear drag (e.g. see Nielsen, J. Sedim. Petrol., vol. 63, 1993, pp. 835–838) only arise in artificial flows that, by design, eliminate preferential sweeping by the eddies. Gravity and inertia both reduce the particle r.m.s. velocities and falling particles are more responsive to vertical than to horizontal fluctuations. The model by Wang & Stock (J. Atmos. Sci., vol. 50, 1993, pp. 1897–1913) captures these trends.

Type
Rapids
Copyright
© 2014 Cambridge University Press 

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