The influence of driving conditions on flow behavior in sheared granular flows

Granular materials may behave like a solid, a liquid, or a gas, depending on the processing conditions. In this study, a two-dimensional annular shear cell was used to investigate the dynamic properties of granular flow when subject to varying driving conditions. The effects of different driving conditions on granular flow were examined by taking images of the motions of granular materials with a high-speed camera. Image processing technology and a particle tracking method were employed to measure velocity, slip velocity, local solid fraction, and granular temperature. The results show a gradual decrease in the velocity profile from the shearing boundary to the stationary wall when only the inner or outer wall rotates. The tangential velocity of granular materials is greater with only a rotating outer wall than with an inner wall rotating singly at the same velocity. The results also show that slip velocity increases in conjunction with wall velocity and decreases if the solid fraction is increased. This study also examined flow behaviors caused by rotating both walls, first in the same direction, and then in opposite directions. The results indicate that granular temperatures in a system with both walls rotating in opposite directions are higher than in a system with walls rotating in the same direction.

► Slip velocity is reduced with the increase of the solid fraction.
► Granular temperature is larger with the opposite driving wall direction.
► Velocity gradient is the dominant parameter to influence granular temperature.