1 Dancing Bubbles in Turbulent Flows: PIV Measurements and Analysis

Two-phase bubbly flows are widely applied in engineering and environmental processes. The interaction of the dispersed phase with the continuous phase has a great effect on transfer processes between the phases. The interstitial relative velocities between the phases and the interfacial area and the shape of the dispersed phase are the key dependent parameters in the drag, heat and mass transfer between the phases. Although the physical understanding of bubbles rise in a liquid is a significant practical importance in many areas of engineering, neither the interactions between bubbles in clusters nor the bubble-induced pseudo-turbulence (i.e., the generation of velocity fluctuations by bubbles and their wakes in a laminar flow) are fully understood. The modeling of bubbly flows with the Computational Fluid Dynamics (CFD) codes requires detailed information about the full field velocity close to the bubble and its wake. Such information is not widely available. Experimental data exist mainly from point measurement techniques, which offer the advantage of having high time resolution, but their spatial resolution is poor, and information about the vorticity field is lacking. Many investigations have been carried out over the past three decades using hot-film and hot-wire anemometry. However, the use of hot film anemometry in two-phase flows, raise many questions that remain unanswered. I