Chute aerators: Pre-aerated approach flow
Long spillways often include more than one chute aerator to assure an appropriate cavitation protection. The first aerator guarantees sufficient bottom air concentration along a limited streamwise distance attributed to deaeration. Further downstream, the air concentration may be insufficient to protect the chute from cavitation damage. There, a second aerator is required whose operation is affected by preaerated approach flow. The present investigation systematically model-tested typical chute aerators with various approach flow features including preaeration. The resulting air entrainment coefficient as the ratio of air discharge entrained into the flow by the water discharge remains practically unaffected. The jet length is also not affected. Downstream of these aerators, the streamwise development of the average and the bottom air concentrations was affected by preaeration: the average value increased, whereas the bottom value marginally decreased. The effect of preaeration was found to be only relevant for average approach flow concentrations exceeding some 20% of the corresponding uniform flow concentration.