ABSTRACT
Aerators are placed in the region where the natural aeration has not reached the spillway floor. The flow in the aerator region is deflected from the floor by a ramp; both the lower and the upper surfaces break up into droplets, and air is entrained into the main flow. As the flow velocity at the boundary of a hydraulic structure increases, the potential for damage to the structure by cavitation erosion also increases. The regions of flow in the aerator are: an approach zone, a transition zone, an aeration zone, the reattachment zone, and the zone in which the air is redistributed. This chapter discusses the importance of the geometry of the aerators and the aerator supply system, and explains the effect of aerators on downstream conditions. The mean velocity of the flow enables the cavitation coefficient and the critical velocity to be determined, and these should be used as a guide in determining the position of the first aerator.
