We present results from a direct numerical simulation of the passive transport of
solid particles by a fully developed turbulent channel flow with a Reynolds number
of 180 based on the friction velocity and the channel half-width. Three particle
sets are studied, ranging in diameter from 0.5 to 1.4 viscous wall units and in
aerodynamic time constant from 0.6 to 56 centreline Kolmogorov time scales. We
use particle number density histograms and fractal dimensions to show that the level
of order in the particle spatial distribution peaks near a Stokes number of unity
based on the Kolmogorov time scale. We then quantify the relationship between this
spatial distribution and the instantaneous flow topology. The results indicate that the
previously reported preferential concentration of particles in low-speed streaks leads
to a suppression of particle velocities in the viscous sublayer and buffer region even
in the presence of streamwise gravitational acceleration. In other regions of the flow,
the particles' non-random spatial distribution is shown to be uncorrelated with the
local flow topology. We compare our results with the experimental data of Kulick et
al. (1994) and Fessler et al. (1994) and confirm that the latter authors' results were
not influenced by turbulence modification.
Preferential concentration of inertial fibres in a turbulent channel flow
