TRANSPORT PROCESS OF TURBULENCE ENERGY IN PARTICLE-LADEN TURBULENT-FLOW

The interactions between dispersed particles and fluid turbulence have been investigated experimentally and numerically in a fully developed downflow channel in water. Particle velocities and fluid velocities i n the presence of 340 mu m and 500 mu m glass beads and 420 mu m cellu lose particles were measured by digital particle image velocimetry. In the presence of particles slightly greater than the Kolmogorov length scale of flow and with a large particle time constant, turbulence ener gy was augmented in the streamwise direction, which means that the ene rgy was transported by means of particle concentration fluctuations. T he dissipation rate in the equation of streamwise component of the Rey nolds stress was also increased. Cellulose particles with a small part icle time constant dissipated the turbulence energy in the streamwise and transverse directions due to particle drag. A multiple time-scale model in which the effect of particle concentration fluctuations on la rge scales of turbulent motion was reflected can present both turbulen ce attenuation and augmentation by particles. The particle concentrati on fluctuations increase the turbulence energy in the production range , which induces increasing the energy transport from the production ra nge to the transfer range and yields finally enhancing the dissipation .