In experimental work on bubbly jets and plumes, most data found in the literature relate to the far field of the flow, where nearly asymptotic conditions prevail (e.g., Iguchi et al. 1995, Iguchi et al. 1997). By contrast , the objective of this work was to experimentally analyze the developing region of bubbly jets (Milenković 2005). The first objective was to systematically estimate experimentally the effect of the void-fraction on the main flow properties such as: mean liquid velocity, standard deviation of the liquid velocity, variance of the liquid velocity, kinetic energy and turbulent stress. The experiments were carried out at different Jet Reynolds numbers (i.e., superficial liquid jet velocity) and void fractions, keeping the bubble diameter as constant as possible by means of a specially designed injector. The second objective of the work was to provide a data basis for comparison with calculations using turbulence codes or models for bubbly flows. In this context, it was interesting to learn for instance whether the classical algebraic Reynolds stress expressions that are based on turbulence models such as the mixing-length model of Prandtl, the k − L model as well as the two-equation models like k − ε are applicable under the flow conditions investigated. These models were applied to own experimental results, first in relation to single-phase jets and then to bubbly jets. The findings of these investigations are that the Reynolds stress models are adequate for the developing region of single-phase jets, whereas for bubbly jets, the Reynolds stress models work well in the jet region, but in the transitional region, where buoyancy begins to dominate, wrong predictions of the turbulent shear stress are obtained.The simultaneous bubble and liquid velocity measurements were conducted with the Particle Image Velocimetry (PIV) technique, whereas the void fraction results were obtained with Double Optical Sensors (DOS).
Milenković et al. (Fri,) studied this question.