Abstract: Aerators are critical devices in preventing cavitation damage in high-velocity spillway structures. However, under the conditions of low Froude numbers and mild slopes, cavity backwater is prone to obstruct aeration holes, affecting aeration effectiveness. Therefore, introducing a flow resistance slope downstream of the aerator is considered as a measure to effectively mitigate the adverse effects of backwater. This paper develops a mathematical model for predicting the volume of water accumulation associated with varying flow resistance slopes through theoretical analysis and experimental tests on a 1:25 scale model, and examines the impact of these slopes on cavity water accumulation in mild slope spillways. This study indicates a flow resistance slope affects water accumulation in the cavity through changing the jet nappe impact angle . For a mild slope spillway, if the effect of the slope change on cavity water accumulation is considered, the cavity conditions can be categorized into three phases: overflow phase, water-blocking optimization phase, and clean cavity phase. In the experimental conditions, when both the blocking and aeration effects are taken into account, the optimal angle occurs in the water-blocking optimization phase (21% < < 41%), where a stable cavity forms under the jet and the contact between water and air is sufficiently enhanced. This study helps optimize the design of aerators on mild slope spillways under low Froude number conditions.

Key words: aerator, slight slope, flow resistance slope, cavity backwater, low Froude number