Structure of turbulent round bubbling jet generated by premixed gas and liquid injection

An air water mixture was injected into a cylindrical water bath through a single-hole bottom nozzle to generate a vertical turbulent bubbling jet. A parameter called jet volume fraction, defined as the ratio of the air flow rate to the total flow rate of air and water, was introduced to specify the bubbling jet. The jet volume fraction was raised from zero to approximately 0.5 in order to study the effects of bubble concentration on the mean flow and turbulence characteristics in the water phase. Bubble diameters were roughly 2 mm and almost independent of the jet volume fraction. Water velocity measurements were made using a two-channel laser Doppler velocimeter. The effect of the jet volume fraction on the axial mean velocity of water was relatively weak, whereas the turbulence characteristics were significantly modulated. Turbulence production was enhanced with an increase in the jet volume fraction. The skewness and flatness factors, however, were not influenced by bubbles and agreed well with their respective values for single-phase free jets. Simplified methods of correlating the axial mean velocity, the root-mean-square values of the axial and radial turbulence components and Reynolds shear stress were proposed.