Effect of packing fraction on granular jetting from solid sphere entry into aerated and fluidized beds

When a solid sphere impacts on a granular bed, a high-speed vertical jet can arise following the collapse of the cavity that is formed by the penetration of the sphere into the bed. The jet then becomes unstable and breaks into discrete clusters due to density inhomogeneities. In this study, the jetting process was observed using high-speed photography and determined to be a function not only of impact velocity and particle size, but also of the packing fraction in the bed during the impact. Experiments were performed for two different bed diameters, two bed heights, and two impact velocities. Under certain conditions, below a threshold packing fraction, the jet is seen to divide into two distinct parts: a thin upper section followed by a thick base. Geometrical constraints are also shown to be critical in determining the dynamics of the jet.