Gas-liquid two-phase flow patterns in the wake of a submerged nozzle under co-flow condition

The present study aims to reveal gas-liquid flow patterns as gas is injected into co-flowing water. An experimental work was conducted in a loop in which pure water was circulated. The gas-injection nozzle was submerged in the flowing water. Effects of the water flow velocity and gas flow rate were jointly considered. Two-phase flow patterns were visualized using the high-speed photography and then analyzed statistically. The evolution of the cavity-water interface and collapse of cavity were explained. The results show that a sequential arrangement of a long attached cavity and dispersed bubbles in the streamwise direction constitutes a unique flow pattern. The cavity length is dependent of the contest between the gas velocity and water flow velocity. A single-valley distribution of pinch-off frequency as the gas/water velocity ratio varies is insensitive to the water flow velocity. At high water flow velocities, collapse of cavity follows the pattern of wake vortices. Distinct coalescence is evidenced at high gas/water velocity ratio as a large gas pocket is separated from the attached cavity. It is ascribed to the retarded motion of the gas pocket and high inertia of the subsequently detached small bubble.