Rapid flow of dry granular materials down inclined chutes impinging on rigid walls

We performed laboratory experiments of dry granular chute flows impinging an obstructing wall. The chute consists of a 10 cm wide rectangular channel, inclined by 50° relative to the horizontal, which, 2 m downslope abruptly changes into a horizontal channel of the same width. 15l of quartz chips are released through a gate with the same width as the chute and a gap of 6cm height, respectively. Experiments are conducted for two positions of the obstructing wall, (i) 2 m below the exit gate and perpendicular to the inclined chute, and (ii) 0.63 m into the horizontal runout and then vertically oriented. Granular material is continuously released by opening the shutter of the silo. The material then moves rapidly down the chute and impinges on the obstructing wall. This leads to a sudden change in the flow regime from a fast moving supercritical thin layer to a stagnant thick heap with variable thickness and a surface dictated by the angle of repose typical for the material. We conducted particle image velocimetry (PIV) experiments by recording the moving material from the side with charge coupled devices (CCD) cameras. The experiment was also video recorded. From the CCD data velocities were also deduced using the PIV technique. In order to compare the results here we describe the experiments for the same material and the same gap width of the silo gate but for the two positions of the obstructing wall. Analysis of the shock front formation and propagation upslope, evolution of the height of the supercritical flow, impact velocity and momentum are presented and discussed in detail. Computed and derived shock front heights match well.