Particle image and tracking velocimetry of solid-liquid turbulence in a horizontal channel flow

The turbulence statistics of the solid and liquid phases in a horizontal turbulent channel flow are experimentally investigated to identify the effect of particle size, flow Reynolds number (Re) and the volumetric concentration of particles. Glass beads with diameters of 285, 340, 530 and 700 pm are used to produce suspensions at particle volumetric concentrations between 0.05 and 0.18%. Measurements are made at Re of 50,000, 75,000, 100,000, and 125,000 based on channel height and average velocity. The instantaneous velocity of the glass beads is obtained using a correlation-based particle tracking velocimetry (PTV) while particle image velocimetry (PIV) using smaller tracers is applied simultaneously to obtain the liquid phase velocity. It is observed that the solid phase velocity is larger than the liquid phase in the near-wall region for the larger particles and higher flow Re. The particle Re number, Rep, defined based on the particle diameter and the slip velocity (mean relative velocity between the liquid and solid phases), and the Stokes number (St) are used to evaluate the turbulence modulation of the liquid phase. Particle Re numbers as large as 225 are calculated for the 700 mu m particles at Re=125,000, which leads to vortex shedding and, consequently, increases turbulence intensity of the liquid phase relative to the unladen flow. The PTV results indicate that the turbulence intensity of the solid phase decreases with increase of St (i.e. larger particles and higher flow Re). The solid phase volumetric concentration has negligible effect on the solid phase turbulence, while the wall-normal turbulence intensity of the liquid phase increases with the volumetric concentration. This observation reveals the two-way coupling of the solid and liquid phases at the range of concentrations investigated in the current study. (C) 2018 Elsevier Ltd. All rights reserved.