Particle-generated turbulence in homogeneous dilute dispersed flows

Abstract

Homogeneous turbulence generated by uniform fluxes of round glass beads (0.5, 1.0 and 2.0 mm dia) falling through stagnant (in the mean) air was studied for particle Reynolds numbers in the range 100-800 and particle volume fractions <0.0004%. Moments, probability density functions, spatial correlations and temporal spectra of air velocity fluctuations were measured using two-point phase-discriminating laser velocimetry. Predictions based on a simplified stochastic analysis, involving linear superposition of randomly-arriving particle velocity fields, were used to help interpret the measurements. Guided by the theory, correlations of turbulence properties were achieved for both the present particle/air and earlier particle/water measurements. Turbulence intensities (referenced to mean particle relative velocities) and integral scales are functions of the rate of dissipation of particle mechanical energy and particle drag properties; however, normalized probability density functions, spatial correlations and temporal spectra are largely independent of particle properties.