The microscopic structure of a granular gas fluidized by turbulent air wakes.*

We study the properties of the velocity distribution function of granular gas of identical spheres; this gas is produced in our laboratory by placing ping-pong balls on a metallic mesh. We then dispose a fan whose air current intensity is controlled at will. The air stream causes turbulent wakes near the balls surface, thus producing Brownian dynamics on the gas. In particular, we analyze the case of not large average packing fractions; i.e., the system can be regarded as a granular gas since particles contacts are short and only between two spheres (thermality in the system is driven only through binary collisions). Using a high speed camera (Phantom VEO410L) we are able to track particles positions at short time invervals. In our presentation, we explain in detail the particle tracking method we use and the information conveyed on the structure of the single particle distribution function as a function of applied air flow. We also provide an analysis in order to deduce the values of particle collision frequency and mean free path in our experiment.