Measurements of the velocity distribution in ping-pong-ball avalanches

Dense-flow avalanches may be simulated as granular flows. In this work, large-scale experiments on ping-pong-ball avalanches are investigated. In one situation, channeled flows with up to 6000 balls are produced. Another set-up is the open, three-dimensional flow over the landing track of a ski-jump field, using up to 300 000 ping-pong balls. The measurements focus on the internal velocity distribution, of the balls as well as of the air. A video camera positioned above the flow allows the measurement of the location and distance of a single ball, which finally leads to its velocity Different profiles in the head and tail as well as other flow properties are obtained. With vertically placed tubes, in and above the flow, the open ends pointing towards the ground, the static pressure depression induced by the air flow is measured and leads to qualitative air-velocity profiles in and above the tail of the ping-pong-ball avalanches.