Drag and lift forces on bubbles in a rotating flow

The motion of small air bubbles in a horizontal solid-body rotating flow is investigated experimentally. Bubbles with a typical radius of 1 mm are released in a liquid-filled horizontally rotating cylinder. We measure the transient motion of the bubbles in solid-body rotation and their final equilibrium position from which we compute drag and lift coefficients for a wide range of dimensionless shear rates 0. 1 < Sr < 2 (Sr is the velocity difference over one bubble diameter divided by the slip velocity of the bubble) and Reynolds numbers 0.01 < Re < 500 (Re is based on the slip velocity and bubble diameter). For large Sr, we find that the drag force is increased by the shear rate. The lift force shows strong dependence on viscous effects. In particular, for Re < 5, we measure negative lift forces, in line with theoretical predictions.