Unsteady Flow Numerical Simulation And Its Application In Cascade Reservoirs

Unsteady flow is usually called as hydraulic transients, which is an unstable process of flow and hydraulic pressure. Flow changing and hydraulic accidents are the common causations leading to unsteady flow. In the operation of cascade hydropower station, when the upstream station's peak is regulated, the unsteady flow may appear at the dam downstream, leading to a comparable change in hydraulic elements. As a result, adverse impact will be made on navigation, especially when the upstream station is in a large scale, the navigation conditions will be worse. Therefore, the unsteady flow caused by peak regulation has been under a lot of attention. The research of the unsteady flow can provide relevant studies with scientific basis, and is regarded as a realist ic subject.This thesis is carried out on the basis of unsteady flow numerical calculations in cascade reservoir and aims to figure out the spread law of unsteady flow when the cascade upstream peak is regulated. Besides, the influence of unsteady flow simulation and analysis of the combined operation mode of cascade stations on navigation is also discussed. When the operation mode of the upstream power station is determined, the combined operation mode of cascade stations and the influence from the initial water level of the downstream station on cascade power benefit are analyzed, providing references to help perfect the cascade operation mode.Based on the unsteady flow calculations, this paper aims to undertake the tasks listed below:(1)Commonly used numerical method is introduced in detail and compared. Finite volume method is used to discrete one-dimensional shallow water equation, and the mathematical model of unsteady flow is also established in this paper. In view of the key problems of the mode, the process of the finite difference method for the unsteady flow mathematical model.Taking the unsteady flow in the diversion canal of a power station as an example, the feasibilities of the mathematical model and calculation method applied to test the unsteady flows are proved.(2) Finite difference method is applied to numerical simulation of unsteady flow of cascade reservoirs. In the presence of peak load regulating operation of the upstream power station, an unsteady flow simulation of three combined operation modes of the cascade station both in its upstream and downstream is conducted, so that the influences on navigation of unsteady flow under different operation modes are concluded. In the end, this thesis studies the influences of the initial water level of the downstream station and of the combined cascade operation modes on power generation and navigation, providing references to help perfect the cascade operation mode.