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Gated conduits involve high-velocity air–water flow. When studies on gated conduits are examined, it is determined that the air-demand ratio changes according to the hydraulic and geometric parameters. However, no study has investigated the effect of the cross-sectional geometry of high-head conduits with a sluice gate on the air-demand ratio. In this study, the effect of conduit cross-sectional geometry on the air-demand ratio is examined. Results indicate that a conduit's cross-sectional geometry has an important effect on the air-demand ratio, especially at 10% and 15% gate opening rates. It is seen that the effect of the conduit geometry on the air-demand ratio decreases at 20%, and for greater gate opening rates. Moreover, a formula for estimated the air-demand ratio is presented, relating the air-demand ratio to the gate opening rate, Froude number, hydraulic radius and conduit length. [ABSTRACT FROM AUTHOR]

Stepped spillways have become a popular method in recent times. Stepped spillways are used commonly for both energy dissipation and aeration. In this study, the energy dissipation ratio and inception point location of stepped spillways with and without end sills were studied using computational fluid dynamic (CFD) methods. The analyses were carried out for two sill types and three s/h ratios. Flow characteristics and air inception points were determined for slope angles of 30°, 40° and 50°. The results were compared and discussed with the other studies in the literature. The greatest energy dissipation ratio was obtained at the slope angle of 30° for type 2A (i.e. stepped sill and s/h ratio of 0·30). Moreover, the greatest energy dissipation ratio was shown at the slope angle of 50° for stepped spillways without end sills. It was found that the length of the non-aerated flow region was closely related to energy dissipation. Finally, the flow characteristics of the stepped spillways can be reliably determined by using CFD analysis. [ABSTRACT FROM AUTHOR]

Air may be entrained into flowing water by design or inadvertently. Air entrained into flowing water at a hydraulic structure may be beneficial from the standpoint of oxygen recharge. When the gate of a high-head outlet conduit is partly opened, a negative pressure draws the air in through the air vent. Air that is entrained into the water is instantly forced downstream in the form of small air bubbles. The solution of oxygen into the water results from the air entrainment downstream of the high-head gated conduit. Moreover, high pressure in high-head gated conduit flow systems also facilitates the solution of oxygen into the water. Numerous model studies and a few field measurements have been conducted to determine the amount of air demand by closed conduits. The literature search did not identify any published analytical or physical studies of the dissolved oxygen levels produced in gated conduits. Therefore, experimental studies were conducted to investigate aeration efficiency of high-head gated conduit flow systems by using a simplified experimental configuration. It was observed from the results that almost full oxygen transfer, up to the saturation value, occurred at high-head gated conduits. Accordingly, it was concluded that high-head gated conduit flow systems have an extremely high efficiency for transferring oxygen from air bubbles to water. [ABSTRACT FROM AUTHOR]