Inside the moving layer of a sheared granular bed

Abstract

The moving layer at the surface of a granular bed sheared by a viscous flow has been investigated experimentally. The fluid and particle velocities have been measured using particle imaging velocimetry (PIV) and particle tracking, respectively, with a technique of matched index of refraction. The mean velocity profiles are found to be parabolic. The models of Bagnold (Phil. Trans. R. Soc. Lond. A, vol. 249, 1956, pp. 235–297) and Leighton & Acrivos (Chem. Engng Sci., vol. 41, 1986, pp. 1377–1384) fail to account for the observations. A simplified model assuming uniform particle concentration provides good agreement close to the threshold.