The Generation and Dynamics of a Granular Jet Induced by a Sudden Acceleration

Granular material is a closely packed collection of a large number of grains, often tens of microns to a few millimeters in size. The complex coupling between a wide range of parameters such as friction between grains, size dispersion, and particle shape makes even the simplest system of granular material challenging to be understood. Recently, it has been reported that when a solid sphere impacts on a deep and loose layer of granular medium, a broad splash of sand is generated, followed by a transient axisymmetric crater, and finally a granular jet is shot up vertically. Interestingly, such similar jets are also observed in ordinary liquid systems. Though such analogues are expected to provide key physical insights, the mechanism behind the phenomenon is not yet understood. Furthermore, it is difficult to investigate the details of the dynamic behavior of jet ejection using previous jet generation methods due to the effects of large deformation of the granular layer and particle scattering. Therefore, we performed an experimental study of jet generation and dynamics of granular material using the mechanism of liquid jet generation by a pressure impulse. We found quantitative similarities between jet phenomena in liquid systems and granular systems.