The Study On Damage Of High Water Head Spillway Tunnel During Operation Period

Spillway tunnels are important drainage structures in water resources and Hydropower projects.They have been widely used in many large and medium-sized water resources and hydropower projects in china.They have the characteristics of high water head,large discharge flow,high velocity and complicated flow pattern,and are extremely vulnerable during operation.Therefore,combined with the hydraulic characteristics of the high head spillway tunnels,the damage under different working conditions during the operation of spillway tunnels have been studied.It is beneficial to optimize and protect the vulnerable parts in the spillway tunnels,improve the safety and reliability of the projects,reduce the daily maintenance and repire cost during the design,construction,operation and management stages of the spillway tunnels.The study is of great significance to provide reference for the design and protection of spillway tunnels.In this parer,based on the actual situation of Zipingpu water conservancy project,the flow fields of No.1 and No.2 spillway tunnels were solved by 3D numerical simulation which adopted the standard k-? two-equation model and used the VOF method of geometric reconstruction format to track the free water surface.The 3D mathematical model of the flow in spillway tunnels were established.The flow field data of spillway tunnels were obtained,including the discharge capacity,flow regime and water suface line,the length of the aerator cavities,the pressure of the bottom and side walls,velocity and cavitation number.The numerical simulation results were in good agreement with the hydraulic model test results,which verified the applicability and reliability of the mathematical model of the spillway tunnels.The SST-DDES turbulence model was used to simulate the fluctuation pressure of flow in NO.2 aerator in NO.1 spillway tunnel.The fluctuation pressure signals were analyzed of time domain and frequency domain characteristics.The results showed that the water flow in the flood discharge tunnel belonged to the category of low frequency water flow.The vibration frequency of flow was mainly distributed in the range of 0?20HZ and the dominant frequency was about 0.12.The fluctuating pressure values of each measuring point obeyed normal distribution and range from-3 to 3 times the RMS of the fluctuating pressure.The fluctuation pressure of aerators in spillway tunnels obeyed the single-peak distribution and were greatly influenced by the adjacent instantaneous values.The numerical simulation results were similar to the hydraulic model test results in changing trend.However,dued to aeration,high flow rate and other factors,there were differences in amplitude and phase between simulated and experimental values of fluctuating pressure.Based on the hydraulic characteristics of the flow field in a high head spillway tunnel,the problems of cavitation,erosion,residual amplitude at the top of tunnels and flow vibration,which are often encountered during the operation of the spillway tunnel were studied and analyzed.According to the damage characteristics of spillway tunnels and the field prototype test data during operation period,the dangerous areas of spillway tunnels were divided and suggestions for design and protection of spillway tunnels were put forward.