地下式水电站尾水洞过渡过程中明满流现象的研究

阐述了地下式水电站尾水洞过渡过程中明满流的转换过程;考虑了这类明满流特有的初始状态和边界条件的影响,对洞内截留空气和进、排气过程作了精心处理,建立了数学模型;进行了大量数值计算与水力学模型试验;深刻阐述了这类明满流现象的机理;讨论了明满流对尾水系统的危害及应采取的工程对策,该研究为类似工程设计和科学研究奠定了一定的理论基础。

Study on Free Surface-Pressurized Flows in Tail race Tunnel of Underground Hydropower Station

In the paper, the transforming process of the free surface-pressurized flows was described in detail. The research reveals that the free surface-pressurized flows must come about on conditions that both tailwater level is close to the top of tunnel outlet and hydropower station changes greatly in load, and the type of free surface-pressurized flows differs greatly from the type of what Wiggert, Charles song and Priessmann studied before. This paper considered systematically the effect of particular initial state and boundary conditions of the flows, dealt with reasonably the trapped air and the process of air suction and exhaust in diversion tunnel, then established a mathematical model. The model is made up of basic equations, state equation of ideal gas, boundary and initial conditions equations. Numerical method of the model used characteristics method. To examine the accuracy of numerical computation, a series of hydraulic model tests were conducted using the model of tailwater systems of ER TAN Hydropower Station. These results of computations and tests display that high both positive and negative pressures are created by the flows, the main reason is that the trapped air in diversion tunnel is stretched and compressed quickly during transients. The three conditions explained in the paper are regarded as the mechanism of the free surface-pressurized flows. Finally, the harm of the flows to tailwater system is analysed and some engineering countermeasures are put forward to reduce it. The research is of great value for engineering design and scientific research.