PARTICLE TURBULENCE INTERACTION IN A BOUNDARY-LAYER

Particle-turbulence interaction in wall turbulent flows has been studied. A series of experiments varying particle size, particle density, particle loading and flow Re has been conducted. The results show that the larger polystyrene particles (1100-mu-m) cause an increase in the number of wall ejections, giving rise to an increase in the measured values of the turbulence intensities and Reynolds stresses. On the other hand, the smaller polystyrene particles (120-mu-m) bring about a decrease in the number of wall ejections, causing a decrease in the measured intensities and Reynolds stresses. These effects are enhanced as the particle loading is increased. It was also found that the heavier glass particles (88-mu-m) do not bring about any significant modulation of turbulence. In addition, measurements of the burst frequency and the mean streak-spacing show no significant change with increase in particle loading. Based on these observations, a mechanism of particle transport in wall turbulent flows has been proposed, in which the particles are transported (depending on their size, density and flow Re) by the bursting events of the wall regions.