Research and Implementation on Aeration in Cavitation-protection for the Sidewalls of Ertan Spillway Tunnel

摘要

Ertan Hydropower Station is the China's largest hydropower project in the 20th century. The power station is equipped with 2 spillway tunnels with inlet raised. The maxi-mum flood discharge of each spillway tunnel is 3800 m3/s and the design maximum velocity is 45 m/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, and low Froude and small bottom slop. Forced aeration device on soleplate is usually introduced to prevent cavita-tion damage of hydraulic structures in engineering. The cavitation corrosion is prevented ef-fectively 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 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 effectiveners of more methods of aeration in cavitati-on-protection for the sidewalls, and the plan was given for spillway tunnel with large dis-charge and high velocity flow. The shape of 2nd aerator was renovated at the spillway tunnel No. 1 of Ertan hydropower station according to the research result in 2005 and a new-style three-dimensional aerator of contracting sidewalls (lateral deflector aerator) with used heav-ing bucket. 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 are in good condition and the cavitation is protected. The cavitation of sidewalls is resolved successfully.