Effect of Froude number on bubble clustering in a hydraulic jump

The study of bubble clustering processes may provide a significant insight in turbulent air-water flows. Previous studies investigated these processes in plunging jets, in dropshafts and in hydraulic jumps. This research investigates the bubble clustering process in hydraulic jumps using experimental data collected in a rectangular horizontal flume with partially-developed inflow conditions for inflow Froude numbers in the range from 6.5 to 14.3. Two criteria for cluster identification were applied: one criterion was based upon a comparison of the local instantaneous water chord time with the median water chord time, whereas the second identified a cluster if the water chord time was smaller than the air chord time of the preceding bubble, i.e. a bubble was in the near-wake of the leading bubble. The results highlight significant patterns in clusters production both over the flow depth and the distance from the jump toe. The effect of the inflow flow Froude number on the clustering process is also discussed.