Analysis of air bubbles probability distribution functions in a large-size dropshaf

Dropshafts are commonly used in sewers and stormwater channels as energy dissipator systems. Since recent effort has been devoted to characterize dropshaft hydraulics and air-water flow properties, and the present paper develops an analysis of the bubbles probability distribution functions (PDF) in a shaft pool using new experiments conducted in a large-size facility. First, theoretical trajectory calculations of the free-falling nappe were compared with the maximum void fraction data observed within the pool. Then, statistical analysis was performed on both air and water chord length data. PDF was derived as well as mean, median, mode, standard deviation, skewness and kurtosis values. Further, these results were compared with some earlier work. The results obtained over the pool length at various vertical elevation highlighted some new insights on the interactions between turbulence, bubble coalescence and detrainment of the air bubbles.