Flow Fields Induced by Bubbles

Characteristics of the surrounding liquid motion induced by a single bubble and a swarm of bubbles were experimentally investigated. Two types of bubbles with different diameters were precisely generated by using a bubble generator and hypodermic needles. PIV measurement was carried out to capture the liquid motion disturbed by the bubbles. The liquid motion was analyzed based on turbulence intensity defined by the standard deviation of liquid-phase velocity fluctuations and the bubble velocity. As a result, the bubble-shape oscillation significantly affects the area of disturbance region. Large shape oscillations on a bubble induce a wide range of fluid disturbances. In addition, it is also clarified that the turbulence intensity measured via 2-dimensional PIV is significantly affected by the bubble motion. Turbulence intensity decreases due to transition from zigzag motion to helical motion of bubbles.