Experimental investigation on the liquid flows induced in a rotating drum*

The rotating drum (circular cylindrical chamber with a short aspect ratio) aligned horizontally, whether it is fully or partially filled with liquid and/or solid particles, is encountered in many engineering applications for mixing, drying, coating, and cleaning. In the present study, the liquid flow induced in a rotating drum is investigated with different fill ratios. For each fill ratio, controlled by varying the water height, we measure the velocity fields at different cross-sectional planes with particle image velocimetry while varying the rotational speed of the drum. We compare the flow structure developed in the partially filled conditions with the condition of a fill ratio of 1.0, in which the liquid inside the drum rotates forming a large-scale organized flow structure. In addition to the mean flow structure, we examine the fluctuating velocity fields together with the dynamics of the free surface. Depending on fill ratio (< 1.0) and rotational speed, it is found that the counter-acting effects by the centrifugal (viscous) and gravitational forces cause quite complicated flow structures inside the drum. We also report the differences between the liquid flow and granular (particle) flow in a partially filled drum.