Granular segregation in narrow rotational drums with different wall roughness: Symmetrical and asymmetrical patterns

Abstract

The axial segregation of granular flows in rotating drums is closely correlated to the material properties and side-wall friction. In this study, experimental work with two different types of sidewall roughness is performed to characterize the frictional effect of the side walls. In one case both walls are smooth and in the other each sidewall has a different roughness. The evolution of the Rayleigh-instability core inside the granular assembly varies with the aspect ratio of the drums. By increasing the Froude number, the axial banding expands with increasing side-wall roughness. The asymmetrical banding stripe is enhanced by the differential frictional roughness on either side wall. Axial segregation is driven by both the variation in the size ratio of the mixtures and the drum geometrical parameters. We performed experiments to investigate the wall friction of dry granular segregation in the rotary drum. The results show that increasing rotational speed, aspect ratio, and changing the wall friction, have significant influences on the segregation phenomenon of mixed granular matter due to the side-wall shear band and Rayleigh-like instability. ► A new asymmetrical pattern on axial plane is observed in the study. ► The asymmetrical axial segregation is sensitive to the side-wall friction. ► The widespread coarse region causes an axial convection on the granular surface.