X-ray study of fast and slow granular flows with transition jump in between

Abstract

Abstract: Flows of dry granular materials on a smooth chute are investigated by X-ray radiography. Discontinuities in height, velocity and density, namely jumps, are produced under different incoming steady-flow conditions by varying the mass discharge and the slope angle. This allows to confirm and further reveal the phase-diagram of standing granular jump patterns with diffuse and weakly compressible jumps that move to steep and highly compressible jumps when increasing the slope angle and/or decreasing the mass discharge. A wide range of steady-flow states before and after the jumps are achieved within each of the different experiments over variable input conditions. The flow densities are then measured relatively accurately by the X-ray radiography. This allows to highlight a transition from the supercritical flows before the jump to the subcritical flows after the jump through hysteresis of the depth-averaged effective friction, if incompressible depth-averaged momentum conservation is considered valid for the regions before and after the jump. In addition, the X-ray data of both free-surface and density profiles across the standing granular jumps are successfully used to further validate a recently-established augmented Bélanger equation for the jump height ratio. Graphic abstract: [Figure not available: see fulltext.].