Air–water flows down stepped chutes: turbulence and flow structure observations

Interactions between turbulent waters and atmosphere may lead to strong air–water mixing. This experimental study is focused on the flow down a staircase channel characterised by very strong flow aeration and turbulence. Interfacial aeration is characterised by strong air–water mixing extending down to the invert. The size of entrained bubbles and droplets extends over several orders of magnitude, and a significant number of bubble/droplet clusters was observed. Velocity and turbulence intensity measurements suggest high levels of turbulence across the entire air–water flow. The increase in turbulence levels, compared to single-phase flow situations, is proportional to the number of entrained particles.