Abstract
For safe spillway discharge of floods, attention is paid to the water flow. The resulting air flow inside the facility, an issue of personnel security, is sometimes disregarded. The spillway in question comprises two surface gates and two bottom outlet gates lying right below. Air passages to the outlet gates include an original gallery and a recently constructed vertical shaft. To understand water-air flow behavior, 3D CFD modelling is performed in combination with the physical model tests. The simulations are made with fully opened radial gates and at the full pool water level (FPWL). The results show that the operation of only the bottom outlets leads to an air supply amounting to ~57 m3/s, with the air flow rates 35 and 22 m3/s to the left and right outlets. The air supply to the right outlet comes from both the shaft and the gallery. The averaged air velocity in the shaft and the gallery are approximately 5 and 7 m/s. If only the surface gates are fully open, the water jet impinges upon the canal bottom, which encloses the air space leading to the bottom outlets; the air flow rate fluctuates about zero. If all the four gates are open, the total air demand is limited to ~10 m3/s, which is mainly attributable to the shear action of the meeting jets downstream. The air demand differs significantly among the flow cases. It is not the simultaneous discharge of all openings that results in the largest air demand. The flood release from only the two outlets is the most critical situation for the operation of the facility. The findings should provide reference for spillways with the same or similar layout.
Highlights
In a high-head dam facility, flood discharge from a surface spillway or low-level outlet leads to high-velocity flow that entrains air in the surface water
A general reference on air entrainment and energy dissipation in spillways and other hydraulic structures is written by Chanson [1]
In Sweden, the dam-safety requirements and changed operation conditions have nowadays led to more frequentthe use of the spillways
Summary
In a high-head dam facility, flood discharge from a surface spillway or low-level outlet leads to high-velocity flow that entrains air in the surface water. The flood discharge structure, with two bottom and two surface gates, is located in the middle of the dam. Outlets therefurbished, installation with of upward-going radial gates, which means safetyBoth level of thewere dam.refurbished, Both outletswith were the installation of upward-going radial they become operable for flood discharge. No matter whether the surface gates operate or not, the high-velocity flow from the bottom outlets entails always air supply. If only the surface gates open for discharge, air supply might necessary. Constructed with the dam, the original air passage is a gallery in the middle spillway pier. At the end of the gallery, the air is sucked into the outlet gate chambers via two door openings middle, 2.22 m by 0.70 m.
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