Result of a simulation performed with a soft-sphere collision model.

View also a movie of the experiment corresponding to the simulated case (an experiment with 1 mm glass beads) and a movie of an experiment showing the hysteresis phenomenon (multiple flow states).

Supercritical shallow granular and hydraulic flow through a contraction: experiment, theory, and simulation. A.W. Vreman, M.. Al-Tarazi, J.A.M. Kuipers, M. van Sint Annaland, O. Bokhove, J. Fluid Mech. 578, 233-269 (2007). PDF