THE EFFECT OF HOMOGENEOUS ISOTROPIC TURBULENCE ON THE SETTLING OF HEAVY PARTICLES

摘要

The experiments were performed in a horizontal wind tunnel, and a grid was used both to induce the turbulent and to inject the water droplets. The water droplets were injected through an array of atomizers embedded in the grid that produced a polydispersed spray uniformly distributed along the central portion of the tunnel. The turbulent Weber number for the droplets was always very small, so the droplets behave as heavy spherical particles throughout the experiments. The carrier flow turbulence was studied using a hot-wire anemometer. Both the mean and the fluctuating velocity were found to be uniform in planes perpendicular to the mean flow, outside of the boundary layers. The decay of the turbulent intensity in the test section is well inside the near region, and following the former, a linear fit can be applied to our data, (U/u')~2 = 38.41(x/M -10.17). The turbulence characteristics obtained from the hot-wire measurements are shown in table 1. It is important to notice that the Kolmogorov length scale in the carrier flow is an order of magnitude larger than the droplet's diameter (both the arithmetic and Sauter mean diameters). Two different experimental techniques were used to characterize the velocity and concentration field of the particles in the flow. Phase Doppler Particle Analyzer was used to measure the horizontal and vertical velocities, as well as the diameter, of the particles. Flow visualizations were used to characterize the spatial distribution of the particles.