Statistical Properties of a Granular Gas Fluidized by Turbulent Air Wakes

摘要

We perform experiments with a granular system that consists of a collection of identical hollow spheres (ping-pong balls). Particles rest on a horizontal metallic grid and are confined within a circular region. Fluidization is achieved by means of a turbulent air current coming from below. Air flow is adjusted so that the balls do not elevate over the grid, as an approach to 2D dynamics. With a high-speed camera, we take images of the system. From these images we can infer horizontal particle positions and velocities by means of particle-tracking algorithms. With the obtained data we analyze: (a) the systematic measurement error in the determination of positions and velocities from our digital images; (b) the degree of homogeneity achieved in our experiments (which depends on possible deviations of the grid from the horizontal and on the homogeneity of turbulent air wakes). Interestingly, we have observed evidences of crystallization at high enough densities.