Particle transport in turbulent curved pipe flow

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.Comment: Bent Pipe, Turbulence, Inertial Particles, Curvature Effect, Dean Vortices, Secondary Motio

Turbophoresis in forced inhomogeneous turbulence

“…The large-scale clustering observed in turbulent pipe flows [41], which is similar to what has been observed in turbulent channel flows in ref. [23], can be analyzed in a similar manner to extract the turbophoretic ratio whose dependence on the Stokes number is similar to what has been observed by us but for the data very close to the wall and near the center of the pipe.…”

Particle Velocity and Acceleration in Turbulent Bent Pipe Flows

“…The effect of the Stokes number is found to be more pronounced on the in-plane motion of the particles, which move inwards along the pipe side walls and then rise quickly across the pipe core. This secondary motion causes intense wall-particle collisions of the heaviest populations and in the strongly curved configuration at the outer bend which in turn induce reflection layers as previously discussed for the concentration map in the companion article by Noorani et al [17]. Such reflectional mixing generates fluctuations of the particle radial velocity higher than in the flow.…”

“…The work extends the analysis of the particle distribution by Noorani et al [17]. The simulations employ an efficient spectral element method for the fluid flow one-way coupled with a Lagrangian tracking algorithm for the solid phase.…”

“…Fig. 9 in [17]). This is linked to the action of the secondary motion on the particles in the initial stage of the simulations.…”

“…The transport of a micro-size particulate phase in turbulent toroidal pipes was investigated in a companion study by Noorani et al [17]. In this first investigation (referred to as bpPart15 in the following) the effect of the curvature on the particle transport and accumulation is examined using DNS of the turbulent flow, and Lagrangian tracking of individual particles in the one-way coupling approximation.…”