Effect of inter-particle spacing on turbulence modulation by Lagrangian PIV

Turbulence modulation by solid particles in a fully developed channel now w as investigated by Lagrangian measurement technique. Digital particle image velocimetry (DPIV) and a high-speed CCD camera mounted on a shuttle moving with particle mean streamwise velocity were used to simultaneously detect particle and fluid information among particles. Two classes of particles at particle volumetric fraction up to 3.32 x 10(-4) were employed to provide characteristic values of length ratio and distance between particles, i.e., inter-particle spacing. Turbulence augmentation by particles greater than the Kolmogorov micro-length-scale was induced by a region of high strain ra te and high vorticity located on both sides of the particles. The rapid dis tortion theory (RDT) applied to dispersed two-phase turbulent flows substan tiates the observed directional non-isotropic structure with an increase in particle volumetric fraction. The enstrophy production was enhanced with d ecreasing values of inter-particle spacing, yielding an increase in the ens trophy among particles. (C) 2000 Begell House Inc. published by Elsevier Sc ience Inc. All rights reserved.