Experimental investigation of turbulence modulation by solid particles in a grid-generated vertical flow

Experimental results dealing with the modulation of grid-generated turbulence by coarse glass particles in a vertical downward channel flow are presented. Glass beads with an average diameter of 700 mu m and a mass loading up to 0.1 kg dust/kg air were brought into the flow by an individually designed particle feeder allowing to vary the initial velocity slip. In order to determine the gas flow characteristics, TiO2 particles with an average size of about 2 mu m were used as tracers. Two mono-plane grids with a mesh size of 4.8 and 10 mm generated an isotropic turbulence which decayed along the test section of 2 m length. The mesh Reynolds numbers for these grids, based on a mean air velocity of U = 9.5 m/s, were Re-M = 3045 and Re-M = 6340, respectively. Distributions of the mean velocity, the turbulence intensity along the channel axis and in different cross-sections obtained by Laser Doppler Anemometer (LDA) are presented. A degradation of signals from the glass particles due to coating of their surfaces by TiO2 particles was observed during the measurements. The decay curves of the turbulence intensity in the streamwise direction showed an attenuation of turbulence intensity of the flow induced by the particles for both grids, while the presence of particles decreased the energy spectra at high frequencies. (C) 2000 Elsevier Science Inc. All rights reserved.