Ping-pong ball avalanche at a ski jump

Abstract

Three dimensional granular flow experiments were carried out on a ski jump with 300,000 ping-pong balls. Since the air drag was a large effect, the flow arrived at a steady state within a short distance. The terminal velocities attained showed a remarkable increase with the number of released balls. In addition, the flow formed a distinct head and tail structure, which has often been observed in large-scale geophysical flows in nature. Similarity analysis is used to show that the experiment corresponds to a natural snow avalanche that runs for several kilometers. Video cameras positioned above the flow allowed the measurement of the location and the distance of a single ball, which finally led to the particle velocity profiles. The static pressure depression measurements in and above the flow showed the air velocity profiles and suggested the strong interaction between the balls and the surrounding fluid(air). Computer simulation of 3-dimensional, inhomogeneous two-phase flows that uses the DEM for the particles and the Reynolds-averaged Navier Stokes equations for the fluid are currently in progress.