Author:
BOIVIN MARC,SIMONIN OLIVIER,SQUIRES KYLE D.
Abstract
The modulation of isotropic turbulence by particles has been investigated
using direct
numerical simulation (DNS). The particular focus of the present work is
on the class
of dilute flows in which particle volume fractions and inter-particle collisions
are
negligible. Gravitational settling is also neglected and particle motion
is assumed to
be governed by drag with particle relaxation times ranging from the Kolmogorov
scale to the Eulerian time scale of the turbulence and particle mass loadings
up to 1.
The velocity field was made statistically stationary by forcing the low
wavenumbers
of the flow. The calculations were performed using 963 collocation
points and the
Taylor-scale Reynolds number for the stationary flow was 62. The effect
of particles
on the turbulence was included in the Navier–Stokes equations using
the point-force
approximation in which 963 particles were used in the calculations.
DNS results
show that particles increasingly dissipate fluid kinetic energy with increased
loading,
with the reduction in kinetic energy being relatively independent of the
particle
relaxation time. Viscous dissipation in the fluid decreases with increased
loading
and is larger for particles with smaller relaxation times. Fluid energy
spectra show
that there is a non-uniform distortion of the turbulence with a relative
increase in
small-scale energy. The non-uniform distortion significantly affects the
transport of
the dissipation rate, with the production and destruction of dissipation
exhibiting
completely different behaviours. The spectrum of the fluid–particle
energy exchange
rate shows that the fluid drags particles at low wavenumbers while the
converse is true
at high wavenumbers for small particles. A spectral analysis shows that
the increase
of the high-wavenumber portion of the fluid energy spectrum can be attributed
to
transfer of the fluid–particle covariance by the fluid turbulence.
This in turn explains
the relative increase of small-scale energy caused by small particles observed
in the
present simulations as well as those of Squires & Eaton (1990) and
Elghobashi &
Truesdell (1993).
Publisher
Cambridge University Press (CUP)
Subject
Mechanical Engineering,Mechanics of Materials,Condensed Matter Physics
Cited by
311 articles.
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