Research On Aeration In Cavitation-Protection For The Sidewalls Of Spillway Tunnel In Ertan Hydropower Station

Ertan Hydropower Station is the China's largest hydropower project completed in the 20th century. The power station is equipped with 2 spillway tunnels with inlet raised. The maximum flood discharge of each spillway tunnel is 3800m3/s and the design maximum velocity is 45m/s. The dragon-raise-head spillway tunnel is widely applied in water conservancy and hydroelectric projects. The representative flow characteristics of the anti-arc bottom of the dragon-raise-head spillway tunnel are high velocity, large-unit discharge, low Froude and small bottom slop. Forced aeration device on soleplate is usually introduced to prevent cavitation damage of hydraulic structures in engineering. The cavitation damage is prevented effectively in many spillway dragon-raise-head tunnels by aeration facility. However, when conventional aeration facility was introduced in spillway tunnel No.1 of Ertan, the anti-arc and its downstream bottom were protected, but the cavitation damage still happened on the sidewalls downstream of anti-arc and it gave bad influence on the safety of the project. Large-scale model tests were performed to study the effectivity of many methods of aeration in cavitation-protection for the sidewalls, and the plan was given for spillway tunnel with large discharge and high velocity flow. The shape of 2nd aerator was renovated at the spillway tunnel No.1 of Ertan hydropower station according the research result in 2005 and a new-style three-dimensional aerator of contracting sidewalls (lateral deflector aerator) with heaving bucket was used. The following prototype observation and inspection indicate that the fluctuating water pressures and the cavitaion noise characteristics are smooth and in reasonable ranges. The shape and structure of 2nd aerator is in good condition and the cavitation is protected. The cavitation of sidewalls is resolved successfully.Basing on previous research and large-scale hydraulic model tests, the cause of cavitation damage to sidewalls in the anti-arc bottom of the large dragon-raise-head spillway tunnel, adopting conventional aeration in cavitation-protection, is investigated. In view of characteristics of running project, several plans of aeration in cavitation-protection to prevent cavitation damage are commended. Model tests and prototype observation for plan and modification shape are compared, the application achievements are introduced that research results applying in Ertan hydropower station.