Abstract

This chapter discusses the aeration mechanisms and flow regions. Aerators are designed to deflect high velocity flow away from the chute surface. The waters taking off from the deflector behave as a free-shear layer with a large amount of interfacial aeration. The flow above an aerator is an application of water jet discharging into air and a type of ventilated cavity flow. Characteristic dimensions are typically: aerator cavity lengths from 1 m to 10 m on prototypes, with mean velocities between 5 m/s and 40 m/s. In the aeration region, air is entrained through both the upper and lower jet interfaces and by plunging jet entrainment at the intersection of the jet with the re-circulating pool formed at the end of the cavity. Experimental data obtained on spillway models show consistently that air bubbles are redistributed downstream of an aeration device as in self aerated flows. The flow is gradually varied and there is a complete analogy between the flow downstream of an aerator and self-aerated flows. The present analysis shows that the detrainment in the impact region can be large and it is proportional to the jet impact angle. The contribution of free-surface aeration in the downstream flow region is very important.

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