Measuring air–water flow properties of a stepped chute with beveled edges

Abstract

The hydrodynamic influence of beveled edges on air–water flow properties in a stepped chute were studied. Air–water flow measurements were made with a double tip phase-detection conductivity probe and an ultrasonic sensor for unit discharges up to 0.565 m²/s in a beveled stepped chute for two interchangeable step heights of 0.1 m and 0.2 m. Flow regimes, the onset of aeration, and the streamwise development of air concentrations, interfacial velocities, and free-surface fluctuations were quantified. Bubble count rates, chord lengths, and their distributions were also derived from measurements with a discussion of the flow physics. A direct comparison of air–water flow properties with vertical steps revealed that bevels elongated and reduced the stability of recirculating cavities, directly influencing flow regimes and reducing the distance to the air-entrainment inception point by 20–30%. At the chute exit, beveled steps produced higher mean air concentrations, greater flow depths and reduced interfacial velocities. These results highlight the value of detailed air–water flow measurements to quantify flow properties and processes that may be used in engineering applications.