Spatial distribution of particles in turbulent channel flow of dilute suspensions

Abstract

We experimentally investigated the kinematics and suspension of particles in the near-wall region of a horizontal turbulent channel flow of water. The particles were glass beads with a diameter of 0.014H, where H is the full channel height. The experiments involved dilute particle suspensions at bulk volumetric concentrations (ϕ) of 0.05, 0.12, and 0.27%, and at Reynolds numbers (Re) of 20,200, 40,400, and 60,500. Measurement of Lagrangian position and velocity of the particles was carried out using 3D particle tracking velocimetry. At the lowest Re, the results showed a large near-wall accumulation of particles due to gravitational settling at all three bulk concentrations. The analysis of turbulence statistics suggested negligible effect due to inter-particle collisions even when the local volumetric particle concentration reached 2%. With increasing Re to 40,400 and 60,500, different concentration profiles were observed for ϕ = 0.05% with respect to the profiles of ϕ = 0.12 and 0.27%. A bi-model particle concentration distribution, with an inner and outer peak, was present for ϕ = 0.05% at Re = 40,400 and 60,500. In contrast, the particles at ϕ = 0.12 and 0.27% had a wall-peaking profile. The autocorrelation function of the streamwise Lagrangian velocity and wall-normal dispersion of the particles showed greater stability of particle motions in the near-wall region for ϕ = 0.12 and 0.27% with respect to ϕ = 0.05% at the two higher Re. The observations are associated with a stronger particle-wall lubrication at the higher volumetric concentrations of ϕ = 0.12 and 0.27%.