NUMERICAL-SIMULATION OF THE TICKING HOURGLASS

Using a two-phase fluid flow model based on kinetic theory for granula r how the oscillatory flow of sand in an hourglass first observed expe rimentally by Wu et al. has been simulated. The oscillations appear to be caused by the interaction between the gas pressure and the flow of sand through the orifice of the hourglass. The simulations confirm th e ticking of the hourglass and the suggested mechanisms for this behav iour found experimentally by Wu et al. The simulations also show bubbl es of air rising through the powder as observed experimentally.