EXPERIMENTAL INVESTIGATION OF A TURBULENT BUBBLY MIXING LAYER

An experimental investigation of a turbulent air-water bubbly flow in a plane vertical mixing layer is presented. An important characteristi c of this bubbly flow is that the slip velocity is of the same order o f magnitude as the liquid velocity. For various inlet conditions of li quid velocity and void fraction, the distributions of velocity, turbul ence intensity and void fraction were measured. The mean velocity fiel ds in both phases present self-similar evolutions that preserve the ma in characteristics of single-phase mixing layer. The spreading rate of the mixing layer is found to be significantly greater in bubbly flow than in single-phase flow. Moreover, the global structure of the flow proved to be sensitive to void fraction contrast at the inlet. The voi d fraction distributions exhibit a pronounced peak in the wake of the splitter plate. This peak decreases in intensity and is displaced sign ificantly in the lateral direction. The turbulence intensity is also g reater in bubbly mixing layers: it is shown that this effect is relate d to the bubble drift velocity. A heuristic model for the separation o f bubble and shear-induced velocity fluctuations is presented and disc ussed. Finally, it is observed that the RMS velocity of the gas phase results from combined effects of turbulent dispersion and self-induced fluctuating motions of the bubbles. (C) 1997 Elsevier Science Ltd.