Analysis of wake structures in bubbly flowsusing Particle Image Velocimetry (PIV)

The flow structure around rising single air bubbles in water and their characteristics, such as equivalentdiameter, rising velocity and shape, was investigated using Particle Image Velocimetry (PIV) and Shadowgraphy in a transparent apparatus with a volume of 120mL. The effect of different volumetricgas flow rates, ranging from 4μL/min to 2 mL/min on the liquid velocity was studied. Ellipsoidalbubbles were observed with a rising velocity of 0.25–0.29 m/s. It was found that a Kármán vortex streetexisted behind the rising bubbles. Furthermore, the wake region expanded with increasing volumetricgas flow rate as well as the number and size of the vortices