Experimental Study And Numerical Simulation Analysis On TailwaterSystem Of Hydropower Station

With the development of underground engineering technology, now more and more hydropower stations are built under ground. If the headrace scheme is used, the long tailrace tunnel will be essential in underground project. Nowadays the single tube and single-unit hydroelectric station have been used widely and skillfully, but it is necessary for some large hydropower stations to use tailrace bifurcated tubes, just as Xiaolangdi, Xiangjiaba, Baishe project and so on. So it is significant to study the transients of long tailrace tunnel with tank or without tank. Some studies have shown that, tail tunnel with slopping ceiling structure can replace the tail surge tank and satisfy the stability requirement of turbine units. Because of the change of tail water level and power-station load, free surface-pressurized flows perhaps take place in main tailrace tunnel, which is one of the concerned problems in engineering.The elementary equations of pressure and open-channel unsteady flow are the essential theory of hydraulic transients of hydropower station. This article has introduced the equations and has summarized the knowledge of tail tank. By the characteristics method that has been properly modified, the program of long tail system has been compiled by FORTRAN to calculate its water hammer, rising ratio of rotational speed of generator and water lever fluctuation of tail rank. It studies the hydraulic dynamic characteristics of long tail system.Through the hydraulic model experiment of Baishe project, the article also studies the flow characteristics in draft tubes. Furthermore two different designs of draft tube are compared and analyzed.For the long tail system with several turbines, one tank and single main tunnel, which has large scale and difficult technology, its flow pattern affects the power benefit and safety reliability of engineering and also influences the design scheme. Through hydraulic transient test, the article compares the experimental result and calculated result.Lastly, the article studies the tail tunnel with slopping ceiling, summarizes the hydraulic characteristics of free surface-pressurized flows, and introduces its numerical analysis in common use. Through model test of Baishe project and primary analysis, the article indicates the critical tail water level that free surface-pressurized flows will take place in main tailrace tunnel.