MEAN FLOW OF A VERTICALLY VIBRATED HOURGLASS

We have investigated the mean flow of a hourglass submitted to vertical vibrations as function of the amplitude a and frequency f=OMEGA/2pi of the vibration (5Hz less-than-or-equal-to f less-than-or-equal-to 100 Hz). We find that the time constant of the flow dynamics is longer than 0.2s, that the flow rate is weakly sensitive to vibrations as far as these ones have a sm enough amplitude (aOMEGA2<g=10m/s2). When aOMEGA2 becomes larger than g and when the frequency is located inside a resonance domain (10Hz<f<80Hz), the flow rate decreases strongly; it even stops at large aOMEGA2 and when 40Hz<k60Hz.