Air-water flow in hydraulic jumps on macro-roughness

Hydraulic jumps are highly complex three dimensional flows with strong energy dissipation and air bubble entrainment associated with intense mixing. To date turbulence and air-water flow observations in hydraulic jumps have been limited to smooth rectangular channels. Herein novel experiments were conducted on a channel with bed macro roughness to characterise the effect of boundary roughness on the air-water flow properties. The results showed distinctive differences including a reduction in hydraulic jump length and upward shift of the roller toe for a rough bed jump. The air-water flow profiles were comparable with larger aeration downstream of the jump toe for the rough bed and a reduction in aeration and interfacial velocity compared to a smooth bed flow towards the downstream end of the jump. The present study highlighted the potential to use macro roughness boundaries to manipulate the flow performance and the re-aeration capabilities of turbulent hydraulic jumps