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Air Demand for a Ramp-Offset Aerator as a Function of Spillway Slope, Ramp Angle and Froude Number

Author(s): S. Gaskin; T. Aubel; G. Holder

Linked Author(s): Susan Gaskin

Keywords: Spillways; Ramp-offset aerator; Air demand; Air concentration; Spillway slope; Ramp angle; Hydraulic models

Abstract: Spillways having high flow velocities are susceptible to cavitation erosion damage. The damage potential can be reduced by aerating the flow. Ramp-offset aerators are frequently used to provide the required air concentration on the spillway bed. The aerator produces a jet which entrains air from both the upper and lower nappe. The highly aerated jet then undergoes significant detrainment upon impact with the spillway bed followed by a more gradual detrainment downstream. A hydraulic model study was undertaken to determine the air demand of a ramp-offset aerator as a function of its geometry in terms of spillway slope and ramp angle and as a function of the flow defined by the Froude number. A rough estimation of the relative detrainment rates was determined by measuring mean air concentration downstream of the aerator. Two empirical equations summarizing the observations give air demand ratio and downstream air concentration as functions of Froude number, spillway slope and ramp angle.


Year: 2003

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