Drag and lift forces on a counter-rotating cylinder in rotating flow

Results are reported of an experimental investigation into the motion of a heavy cylinder free to move inside a water-filled drum rotating around a horizontal axis. The cylinder is observed to either co- or, counter intuitively, counter-rotate with respect to the rotating drum. The flow was measured with particle image velocimetry (PIV), and it was found that the inner cylinder significantly altered the bulk flow field from the solid-body rotation found for a fluid filled drum. In the counter-rotation case, the generated lift force allowed the cylinder to freely rotate without contact with the drum wall. Drag and lift coefficients of the freely counter-rotating cylinder were measured over a wide range of Reynolds numbers, 2,500 $<$ Re $<$ 25,000, dimensionless rotation rates, 0.0$ < \alpha < $1.2, and gap to cylinder diameter ratios 0.003 $< G/2a <$ 0.5. Drag coefficients were consistent with previous measurements on a cylinder in a uniform flow. However, for the lift coefficient considerable larger values were observed in the present measurements. We found the enhancement of the lift force to be mainly caused by the vicinity of the wall.