Bubbly free and impinging jets: Experimental study by means of PIV and PFBI

Abstract

In the paper, an experimental investigation of the turbulent structure of bubbly free and impinging jets was carried out by means of PIV and PFBI techniques. PIV was applied to measure velocity distributions and turbulent characteristics in the continuous phase, while the PFBI approach was applied to visualize bubbles in the flow and evaluate their sizes. The flow was studied at the Reynolds number of 12,500 and three void fractions β = 0, 1 and 2%. The mean air bubble diameter was estimated to be roughly 0.8 mm for all β. It was revealed that, in the free jet, the air bubbles reduce the jet core size by more than 30% at the distance of a half of the nozzle diameter. In the two-phase jet, the radial velocity fluctuations rise faster in the mixing layer in the initial jet region between the nozzle edge and the downstream position of 40% of the nozzle diameter but further downstream they are suppressed about two times by the bubbles. In the impinging jet, the bubbles produce a high peak of the radial component of turbulent fluctuations near the wall at the distance of 70% of the nozzle diameter from the jet axis.