Particle transport in turbulent curved pipe flow

TL;DR

This study uses direct numerical simulations to analyze how pipe curvature influences the transport, accumulation, and distribution of inertial particles in turbulent flow, revealing significant effects even with slight curvature.

Contribution

It provides detailed insights into particle behavior in curved pipes, highlighting the impact of curvature on concentration, streak formation, and particle depletion zones, which advances understanding beyond straight pipe models.

Findings

Particle concentration at the inner bend wall increases significantly with curvature.

Helicoidal particle streaks form near the wall, varying with secondary flow strength.

Depletion of particles in the core of Dean vortices depends on pipe curvature.

Abstract

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.