Free-surface aeration and momentum exchange at a bottom outlet

This study aims to provide some new understanding of the air-water flow properties in highvelocity water jets discharging past an abrupt drop. Such a setup has been little studied to date despite the: relevance to bottom outlets. Downstream of the step brink, the free-jet entrains air at both upper and lower air-water interfaces, as well as along the sides. An air-water shear layer develops at the lower nappe interface. At the lower nappe, the velocity redistribution was successfully modelled and the velocity field was found to be similar to that in two-dimensional wake flow. The results highlighted further two distinct flow regions. Close to the brink (We(x) < 5000), the flow was dominated by momentum transfer. Further downstream (We(x) > 5000), a strong competition between air bubble diffusion and momentum exchanges took place.