Turbulence modulation by solid particles in a fully developed channel flow was 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 rate and high vorticity located on both sides of the particles. The rapid distortion theory (RDT) applied to dispersed two-phase turbulent flows substantiates the observed directional non-isotropic structure with an increase in particle volumetric fraction. The enstrophy production was enhanced with decreasing values of inter-particle spacing, yielding an increase in the enstrophy among particles. (C) 2000 Begell House Inc. Published by Elsevier Science Inc. All rights reserved.
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