Characteristic gas cavity patterns formed with gas injection into horizontally co-flowing water

Abstract

The present study aims to reveal two-phase flow characteristics as gas is injected into co-flowing water. A computational fluid dynamics work was conducted using the volume of fluid model and the delayed detached eddy simulation. The numerical scheme was validated through experimental results. Effects of the upstream water velocity and the gas injection rate on flow patterns were investigated. Characteristics of gas cavities were compared under different operating conditions. In both experimental and numerical results, unique patterns of gas cavities are obtained. A large cavity is attached to the nozzle outlet, and simultaneously, bubbles are shed from the cavity front. With increasing gas injection rate, the attached cavity is pinched off as it extends in a streamwise direction. As the velocity of water increases, scattered pinch-off frequencies are evidenced and cavity instability is enhanced. Liquid wake downstream of the nozzle contributes significantly to the collapse of the gas cavity. A long and stable gas cavity is produced at high upstream water velocities and gas injection rates.