Hydraulic Transients Research On Free-flow Tunnel Of Conduit System Of Hydropower Station

Hydraulic transients on free-flow tunnel have to be a ticklish task in some connected cascade hydropower development. There are some problems in the conduit system with free-flow tunnel for designers needed to be resolved such as how to ensure the water surface in the tunnel in ordinary operation, how to limit water fluctuations to a permit scope when load rejection occurs, how to avoid the free surface-pressurized flows in this conduit system and what is the best layout of a conduit system. Because of the particularity and the complexity of water power plant hydraulic transient phenomena, it's necessary to make some detail researches focus on the free-flow tunnel of hydropower plant. A practical application model with free-flow tunnel of Wanyi power station is built and tested in laboratory and a mathematical model is established by explicit finite-difference method also called diffusive scheme method. By experiment, some special problems on free-flow tunnel are resolved, as well as the curves of the variation process of water fluctuation are gained. Based on the production of model experiment, suggestions are given to mend the project design. For mathematical model kinds of different boundary conditions related to the free-flow tunnel are discussed and the comparison of explicit and implicit finite-difference is taken. Corresponding calculation programs and many calculation items were developed. The results of numerical simulation are verified by the experiment test, so the mathematical model and the calculation method we give are proved reasonable. The different layouts for overflow weir are studied specially. Compared with the numerical simulation results, the conclusion can be drawn that the overflow weir for cascade hydropower plant should lay in the downstream of the free-flow tunnel if landform and geology are in agreement.