Velocity and air concentration in air-water flow: application on a stepped spillway without sidewalls

Abstract

Until now, hydraulic research of stepped spillways has focused on characterizing aspects as: the different types of flow that occur on the chute, the air inception processes, the potential negative effects associated to the risk of cavitation, the energy dissipation produced by the steps, or the discharge capacity of the spillway. These investigations, however, have focused on stepped spillways with sidewalls, which impose a constant width along the dam. This paper shows the first results of the Collaborative Applied Research project ALIVESCA, conducted between Dragados S.A., the FLUMEN Institute and the Centre for Hydrographic Studies of CEDEX. The project aims to analyze the hydraulic behavior of stepped spillways without sidewalls and establish new criteria for the design of these structures. On the construction viewpoint, avoiding the sidewalls will reduce costs and risks in the project execution. Specifically, the paper aims to analyze the velocity and the air concentration measurements over a spillway model. In particular, aeration is one of the most effective mechanisms to reduce the risk of cavitation damage because the air-water compressibility absorbs the impact of collapsing vaporized bubbles.