Predicting the filling of ventilated cavities behind spillway aerators

Cavitation damage to spillway surfaces may be prevented with the use of aeration devices. These serve to introduce air into the layers close to the channel bottom in order to reduce cavitation erosion. Under some circumstances, the aerator can be drowned out, will cease to protect the spillway surface, and act potentially as a cavitation generator. This article analyses the conditions of filling. Then experimental data for ten aerator geometries are reviewed. Depending upon the aerator geometry, the cavity filling occurs when the Froude number is less than a critical value or when the ratio of the flow depth over the total offset is larger than a characteristic value.