Three-dimensional Unsteady Numerical Simulation Of The Emergency Shut-down Process For Ring Gate Of Hydraulic Turbine

Main research of this dissertation focuses on the three-dimensional unsteady numerical simulation of the emergency shut-down process for ring gate of hydraulic turbine and computational fluid dynamics (CFD) method is used in this simulation, in order to get the hydraulic characteristics of the ring gate, the operation condition of the Francis turbine, and the optimization of the emergency shut-down methods of the ring gate. The main research contents and results are listed as follows:(a) To factually study the unsteady flow inside the ring gate with the calculation area divided by unstructured meshes and RNG k-εturbulence models, the whole-passage in hydraulic turbine is regarded as the main research object basically considering the interactions between the ring gate and its neighboring components. And also dynamic mesh, sliding mesh, multi-phase flow model, and SIMPLEC algorithm, etc. are also used in the simulation of two different kinds of emergency shut-down methods based on the operation situation of Nansha hydroelectric power station.(b) Numerical simulation is made on the commonly used 60 seconds shut-down process and an optimized way of two-stage 26 seconds shut-down process research models. The pressure contours of the inner surface, outer surface and the bottom surface of the ring gate, and the pressure and velocity distribution on the flow field nearby the ring gate, as well as the force status of the valve, the hydraulic characteristics of the diversion components such as the spiral case, stay vanes and guide vanes are obtained under different gate opening. The similarities and differences of the hydraulic characteristics between the two emergency shut-down methods are obtained during the further detailed comparative analyses. Through all the comparative analyses on the hydrodynamic characteristics made herein, not only the operation condition of the Francis turbine can be predicted, the choice of which emergency shut-down methods can be made according to the actual situation of the hydroelectric power station, but also the theoretical basis for both the design and the operation parameters of the electro-hydraulic synchronous control system of ring gate for hydraulic turbine can be provided.(c) Two different shapes of the bottom face of the ring gate are numerically simulated, and the detailed pressure and velocity distribution contours are obtained. Further comparative analyses are made and the influence of the bottom face shape of the ring gate is discussed. The research and conclusions are used in the theoretical support which decision as to the bottom shape of the ring gate should be preferred with respect to the flow pattern analyses provided in this academic dissertation.