Experimental study of bubble-drag interaction in a Taylor-Couette flow

Abstract

This study is an experimental investigation of the interactions between the bubbles, the coherent motion and the viscous drag in a Taylor Couette flow, for the outer cylinder at rest. The cylinder radius ratio  is 0.9. Bubbles are injected through a needle at the bottom of the apparatus inside the gap. Different bubble sizes are investigated (ratio between the bubble size and the gap width 0.05 and 0.12) for very small void fraction (≤0.012). Different flow regimes are studied corresponding to Reynolds number Re based on the gap width and the velocity of the inner cylinder ranging from 400 to 20000. For these Re values, Taylor vortices are persistent leading to an axial periodicity of the flow. PIV measurements of the liquid flow features, bubble tracking in a meridian plane and viscous torque of the inner cylinder measurements are performed. This study provides a first evidence of the link between the bubble localisation, the Taylor vortices and viscous torque modifications. Bubbles are attracted towards the inner cylinder, due to the rotation of the cylinder. For small buoyancy effect, bubbles are trapped and induce a decrease in the outflow intensity, thus leading to an increase of the viscous torque. When buoyancy induced bubble motion, by comparison to the coherent motion of the liquid is increased, a decrease in the viscous torque is suspected.