A study of air entrainment. Application to spillway design

Cavitation erosion damage to spillway surfaces may be prevented with the use of aeration devices, called aerators. These serve to introduce air in the layers close to the channel bottom in order to reduce the cavitation damage. The performances of spillway aerator are studied with data obtained on a steep spillway model and high velocities (from 4 m/s up to 15 m/s). Air concentration and velocity profiles at various cross sections above and downstream of the aerator are presented and analyzed. They provide a better understanding of the air entrainment processes occurring above a bottom aerator. A new analysis the flow downstream of an aerator is presented and this contributes to a new method for the determination of aerator spacing.