Aeration of skimming flow on stepped spillway combined with flaring gate piers

The aeration characteristics of skimming flow on stepped spillway combined with flaring gate piers were studied by model test and analysis on prototype observation data. It is found that in order to mitigate cavitation damage possibly happened to the surface of stepped spillway, the first 6 to 8 steps must be designed to form the aerated flow with cavity. The aeration of flow relates to the type and height of the bucket for generating the aerated overflow at the top of spillway and the type of flaring gate piers. The influence of step height on air concentration is negligible. The slop of stepped chute remarkably affects the air concentration of flow. The steeper the slope, the more rapidly reduced air concentration will be. The air concentration increases with the increase of discharge per unit width. The air concentration of overflow on stepped spillway combined with Y-type flaring gate piers is the highest, and that of overflow on stepped spillway combined with X-type flaring is lower. The lowest occur to the stepped spillway without flaring gate pier. The air concentration in overflow of stepped spillway combined with Y-type or X-type flaring gate piers can meet the requirement for preventing the occurrence of cavitation.