Abstract
The average settling velocity of heavy particles under a body force
field is studied
numerically in stationary homogeneous isotropic turbulent flows generated
by the
direct numerical simulation and the large eddy simulation of the continuity
and
Navier–Stokes equations. The flow fields corresponding to different
selected ranges of
turbulent scales are obtained by filtering the results of the direct numerical
simulation,
and employed for calculating the particle motion. Wang & Maxey (1993)
showed that
as a consequence of the particle accumulation in the low vorticity region
and the
preferential sweeping phenomenon, the average settling rate in turbulence
is greater
than that in still fluid. In the present study, the phenomenon of particle
accumulation
in the low vorticity region is found to be controlled mainly by the small
scales
with wavenumber kω corresponding
to the maximum of the dissipation (vorticity)
spectrum. However, the increase of the average settling rate,
〈ΔvS〉, also depends
strongly on the large energetic eddies. The small eddies with wavenumber
greater
than 2.5kω have essentially no effect on
the particle accumulation and the average
settling velocity. The large eddy simulation is thus adequate for the present
study
provided the smallest resolved scale is greater than
1/(2.5kω). Detailed calculations
show that 〈ΔvS〉
is maximized and is of order u′/10 when
τp/τk≈1 and
vd/u′≈0.5
for Rλ=22.6–153, where τp
is the particle's relaxation time, τk is the
Kolmogorov
timescale, vd is the settling rate in still
fluid,
u′ is the root mean square of the velocity
fluctuation, and Rλ is the Reynolds number
based on the Taylor microscale.
Publisher
Cambridge University Press (CUP)
Subject
Mechanical Engineering,Mechanics of Materials,Condensed Matter Physics
Cited by
96 articles.
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