Experimental investigations of crater formation on granular bed subjected to an air-jet impingement

The crater formation on granular particle beds is important for engineering applications, chemical and process industries as well as for an explanation of related natural phenomena. In this article, experimental studies on the formation of a crater and the subsequent movement of granular particles are carried out. Granular beds consisting of mono-dispersed or poly-dispersed spherical glass-beads are subjected to an air-jet impingement. The impinging air-jet causes creation of craters of various sizes and shapes (such as saucer shape, parabolic shape, parabolic shape with an intermediate region, U shape, and craters with conical slants with a curved bottom surface). The experimental observations reveal two predominant regimes, categorized based on the crater stability, namely, a stable regime or an unstable regime. The mechanisms for the crater formation such as viscous erosion, diffused gas eruption, bearing capacity failure, and diffusion driven flow or combination of them are identified. It is observed that the steady-state depth of a crater increases linearly with an increase in the air-jet flow-rate. The temporal growth of crater depth shows logarithmic variation for a given flow rate. A regime map of the observed crater shapes is presented.