Influence of cross-section geometry on air demand ratio in high-head conduits with a radial gate

Alp Bugra Aydin,Fahri Ozkan,Muhammed Cihat Tuna,Ahmet Baylar,Mualla Ozturk

doi:10.2166/ws.2021.162

Alp Bugra Aydin, Fahri Ozkan + Show 3 more

Open Access

https://doi.org/10.2166/ws.2021.162

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Abstract

Abstract When the gate of a high-head conduit is partly opened, 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 air bubbles. When studies on high-head gated conduits were examined, it was determined that the air demand ratio varied depending on many hydraulic and geometric parameters. This work has focused on determining the effect of conduit cross-section geometry on the air-demand ratio. A series of experiments were carried out on high-head radial gated conduits having different cross-section geometries. Experimental results showed that conduit cross-section geometry had an important effect on the air demand ratio especially in small gate opening rates. Further, design equations for the air demand ratio are presented relating the air demand ratio to Froude number, gate opening rate, and the ratio of gate opening to conduit length.

Highlights

High-head gated conduits are widely used for various purposes such as emergency draining of dam reservoirs, regulation of water levels in reservoirs, preventing sediment accumulation at dam bases, aeration of water and wastewater treatment, etc
Cross-sectional geometry does not have a significant effect on Qa/Qw at gate opening rates greater than 10%
By using the air vent, the air in the atmosphere is drawn into the conduit and the pressure of the gate downstream is kept at safer levels (Figure 1)

Summary

Introduction

High-head gated conduits are widely used for various purposes such as emergency draining of dam reservoirs, regulation of water levels in reservoirs, preventing sediment accumulation at dam bases, aeration of water and wastewater treatment, etc. High-speed flow can cause various structural damage, such as cavitation, due to the effect of the micro-bubbles it contains (Tullis 1989). Cavitation begins to occur as soon as the pressure in the conduit. To reduce or eliminate this damage, air vents are placed downstream of the gate where the flow speed is high. By using the air vent, the air in the atmosphere is drawn into the conduit and the pressure of the gate downstream is kept at safer levels (Figure 1)

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