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On the Average Settling Rate of Heavy Particles in Decaying Homogeneous Isotropic Turbulence

Published online by Cambridge University Press:  05 May 2011

C. Y. Yang  and
U. Lei
C. Y. Yang*
Affiliation:
Institute of Applied Mechanics, National Taiwan University, Taipei, Taiwan 10617, R.O.C.
U. Lei*
Affiliation:
Institute of Applied Mechanics, National Taiwan University, Taipei, Taiwan 10617, R.O.C.
*
*Doctor
**Professor
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Abstract

The average settling rate of spherical solid particles, 〈vs〉, under a body force field is studied numerically in decaying homogeneous isotropic turbulent flows generated by the direct numerical simulation of the continuity and Navier-Stokes equations. The increase of the average settling rate, 〈Δvs〉, is maximized when Tp/Tk ≈ 1 and vd/u′ ≈ 0.5, and is of order 0.lu′, which is qualitatively similar to that in stationary turbulence. Here 〈Δvs〉 = 〈vs〉 − vd, Tp is the particle's relaxation time, Tk is the Kolmogorov time scale, vd is the settling rate of particles in still fluid, and u′ is the root mean square of the fluid velocity fluctuation. However, the magnitude of the maximum value of 〈Δvs〉 in decaying turbulence is substantially greater (about 40%) than that in the corresponding stationary turbulence due to the inertia response of particles to turbulence decay. Although 〈Δvs〉/u′ does not reach a stationary state as the flow is evolving, it is a slowly time varying function for the parameters of interest as Tp (≈ Tk when 〈Δvs〉 is maximized) is in general of one order less than the time scale of turbulence decay.

Keywords

Average settling rate of particlesDecaying homogeneous isotropic turbulenceDirect numerical simulation (DNS)
Type
Articles
Information
Journal of Mechanics , Volume 14 , Issue 3 , September 1998 , pp. 111 - 118
Copyright
Copyright © The Society of Theoretical and Applied Mechanics, R.O.C. 1998

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