The Champati Slide

Abstract

Here, we report some novel findings of chute experiments with native Nepalese granular seeds, called Champatis, and when mixed with other food grain of a fundamentally different physical properties, Silam. The epitomic supergrain Champati exhibits complex frictional, spin and rolling motion. We hypothesize that the Champati slide results in an essentially unique dynamical spreading, separation from other grains, mobility, run-out and deposition morphology. Particularly, the surface anatomy of Champati acted vitally in characterizing these aspects. We reveal spectacular dynamical flow obstacle interaction and depositional behaviour of Champati and the mixture slide. Champati slide manifests hyper-spreading in the run-out. Soon after the mass hits the ground, the behaviour is unprecedented and unpredictable, mainly around the frontal periphery. The very special properties of Champatis control the frontal spreading, rapid grain marching and the zigzag sporadic Champati motion. Particle rolling, spinning, exceptionally lower frictional energy dissipation and grain collision played the major role resulting in an unexpectedly longer travel time and distance, explaining the astonishing hypermobility of Champati grains. The obstacle substantially changes the flow dynamics as the Champati has the higher object mobilization capacity. Due to the unique property of the supergrain, the eye-catching, amazingly strong separation of Champati from Silam evolves swiftly right after the flow inception, and the process intensifies quickly. The separation length characterizes the complex interfacial momentum exchange between the phases in the mixture. The separation length between the frontal Champatis and Silam grains increases exceptionally as it does between the main body and the exclusively Silam-covered tremendously long tail of the flow in the inclined portion of the channel. These results may be useful in better understanding the phase separation, super-wide-spreading and hypermobility of some geological flows, including fragmented rock avalanches, probably helping resolve some relevant standing challenges.