Abstract
Due to the high flow velocity and easy cavitation of high-head drainage tunnels, it is usually necessary to set up aeration facilities. In particular, when the bottom slope of the tunnel is mild, the aeration facilities often have problems such as difficulty with air intake, short cavity, and serious water accumulation, which aggravate the risk of cavitation damage. In this paper, based on the Rumei hydropower station and the Gushui hydropower station, a method combining theoretical analysis and model testing is used to solve the connection problem between the aeration facility and the 3% mild bottom slope of a tunnel body, and the aeration facility shape of “lifting ridge + flat (mild) slope + steep slope” is put forward. The research shows that the steep slope section can smoothly connect the water flow over the cantilever, reduce the jet impact angle, prevent the water from backtracking, and produce a long and stable cavity in the flat (mild) slope section. The aeration concentration along the bottom of the tunnel is higher than 3% at 140 m over the top of the dam. The aeration effect of this type is better, and it can provide effective long-distance protection for a drainage tunnel with high head and a mild bottom slope.
Highlights
Cavitation erosion was first found in military destroyers and turbine propellers and appeared 30 years later in high-head drainage structures of hydropower projects
Cavitation erosion damage is the main hydraulic safety risk faced by high-head drainage tunnels, which seriously endangers the safe operation of drainage buildings
For a spillway tunnel with a mild bottom slope, when the water head is high, the Fr number is low, and the aeration facility is prone to problems such as cavity instability, serious water accumulation, and difficulty with air intake, it cannot effectively perform its aeration erosion reduction function
Summary
Cavitation erosion was first found in military destroyers and turbine propellers and appeared 30 years later in high-head drainage structures of hydropower projects. For a spillway tunnel with a mild bottom slope, when the water head is high, the Fr number is low, and the aeration facility is prone to problems such as cavity instability, serious water accumulation, and difficulty with air intake, it cannot effectively perform its aeration erosion reduction function. The model test was designed using the gravity similarity criterion, and the geometric scale Lr. The empty sand flushing tunnel of the Gushui is composed of aeration sill and the downstream bottom slope werehydropower carried out. We propose an aeration an inlet section, access gate chamber, pressurized section, underground working gate facility shape of “lifting ridge + flat (mild) slope + steep slope”, which is suitable for a chamber, and bottom flip lifting section.
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