Modified Bottom Air Entrainment Estimate by Chute Offset Aerator

Abstract

Offset aerators are a common design for the prevention of cavitation damage to chute spillways. The aeration capacity is linked to the offset air cavity length and jet velocity. Observations suggest that air entrainment may not take place at the lower jet surface immediately at the offset brink, and only a portion of the entrained air is transported into the downstream chute flow. Based on new air–water flow measurements and visualization, a modified model to estimate the air entrainment rate is proposed by considering the effective air cavity length and air detrainment at the jet impact on the chute bed, with a discussion of the calculation of air entrainment flux at the flow free surface. The refined prediction of air entrainment rate highlights the significance of flow Froude number, air cavity length, and jet impact angle for aerator design.