Two-Phase PIV-LIF Measurements in a Submerged Bubbly Water Jet

Abstract

A two-phase air-water shear flow generated by a submerged jet and characterized by a relevant void fraction and laden with fluorescent particles has been investigated experimentally by means of particle image velocimetry (PIV) combined with the laser-induced fluorescence (LIF). Two air-water data sets have been recorded in order to explore two different regimes, namely two-way coupling and four-way coupling, according to air–water interactions. A novel robust discrimination algorithm based on the geometric features and pixel intensity of tracers and bubbles has been introduced and validated. A statistical analysis of the flow field for the two phases and of the bubble-phase geometric features and distribution has been conducted. The increase of the air-flow rate involves an upward orientation of the jet due to the interaction between the air bubbles’ buoyancy forces and the water, with a turbulence increase. Furthermore, greater interactions between air bubbles grouped in clusters occur, backed up by less variation of the air bubbles’ shape and orientation passing from the jet zone to the zone above the same. The results of this study have led to better knowledge of bubble–water and bubble–bubble interactions and to an estimation of the effects of air bubbles in the shear layer of a bubbly water jet.