Author Description

"Hydraulic jumps are commonly employed as energy dissipators to guarantee long-term operation of hydraulic structures. Thus, a comprehensive and in-depth understanding of their main features is fundamental. In this context, the current study focused on a hydraulic jump with low Froude numbers (Fr1 = 2,1 and 2.4) and a relatively high Reynolds number (Re = 2×105 ). Experimental tests employed dual-tip phase-detection probes and two ultra-high-speed video cameras to provide a comprehensive characterisation of the main air-water flow properties of the hydraulic jump in terms of void fraction, bubble count rate and interfacial velocities. Importantly, this research focused on the air-water flow property distribution across the channel width, revealing lower values of void fraction and bubble count rate next to the sidewalls as compared to the channel centreline. Such a spatial variability in the transverse direction questions whether data near the walls may be representative of the flow behaviour in the centreline, raising the issue of sidewall effects in image-based techniques. Herein, ensembleaveraged turbulence statistics were extracted from the optical flow data. The results suggested that the flow region near the roller toe and in the shear layer dissipated the largest proportion of turbulent kinetic energy. The Hinze scale was derived, showing that the bubble-turbulence interplay followed both sub-Hinze and super-Hinze break-up schemes. Overall, the findings provide helpful information to both researchers and practitioners for a better understanding of the physical process, leading to an optimised design of hydraulic structures."--Abstract.