Characteristics of air-water layers along the nappe over spillway aerators

摘要

Aeration of high speed flow is one of the most economical and technically feasible solutions for the control of cavitation on the spillways and tunnels of a high head dam. To enable the proper design of an aerator device, information about the aeration mechanism and its effective parameters is necessary. Although much research has been carried out on aerators, studies regarding the mechanism of air-water mixture along the nappes is insufficient. This is mainly due to the difficulties in measuring the air-water flow parameters. In the present work, the characteristics of air-water layers along the jet aerator have been studied with the aid of a physical model, and the concentration of air-water mixture was measured using an electrical resistivity probe. Air discharge to the lower nappe was calculated by measuring the negative pressure in the air duct using a highly sensitive manometer. Based on these studies, relationships are proposed for the estimation of air concentration across the upper and lower nappes, nappe disintegration length, air discharge entrainment into the lower nappe, inner core decay angle, and lateral spread angle of the nappe.