  Direct numerical simulations (DNS) of particle-laden turbulent flow in
straight, mildly curved and strongly bent pipes are performed in which the
solid phase is modelled as small heavy spherical particles. A total of seven
populations of dilute particles with different Stokes numbers, one-way coupled
with their carrier phase, are simulated. The objective is to examine the effect
of the curvature on micro-particle transport and accumulation. It is shown that
even a slight non-zero curvature in the flow configuration strongly impact the
particle concentration map such that the concentration of inertial particles
with bulk Stokes number 0.45 (based on bulk velocity and pipe radius) at the
inner-bend wall of mildly curved pipe becomes 12.8 times larger than that in
the viscous sublayer of the straight pipe. Near-wall helicoidal particle
streaks are observed in the curved configurations with their inclination
varying with the strength of the secondary motion of the carrier phase. A
reflection layer, as previously observed in particle laden turbulent S-shaped
channels, is also apparent in the strongly curved pipe with heavy particles. In
addition, depending on the curvature, the central regions of the mean Dean
vortices appear to be completely depleted of particles, as observed also in the
partially re-laminarised region at the inner bend. The turbophoretic drift of
the particles is shown to be affected by weak and strong secondary motions of
the carrier phase and geometry-induced centrifugal forces. The first and
second-order moments of the velocity and acceleration of the particulate phase
in the same configurations are addressed in a companion paper by the same
authors. The current data-set will be useful for modelling particles advected
in wall-bounded turbulent flows where the effects of the curvature are not
negligible.
