Research On Hydraulic Characteristics And Stability Control Strategy For Ring Gate Shut-down Water Process Of Hydroturbine With Multi-cylinder Synchronous System

With the purpose of studying hydraulic characteristics of ring gate in shut-down water process and multi-cylinder synchronous system, this dissertation mainly deals with numerical simulation of shut-down process with use of computational fluid dynamics, mathematic modeling on synchronous system along with stability control strategy. The main contents and contributions of this dissertation are listed as follows.(a) Dynamic mesh, RNG k-εmodel, multi-phase model and sliding mesh are used in order to perform three dimensional unsteady numerical simulation of ring gate in Nansha Hydropower Station on Honghe River during shut-down water process, which is different from the widely used model experiments and simulates hydraulic characteristics to avoid runaway phenomenon.(b) Hydraulic characteristics such as pressure distribution, the axial hydrodynamic force, the flow rate, the efficiency and hydraulic loss are analyzed. And the characteristics of flow field near ring gate are also presented. In addition, optimized closing motion style is provided according to axial hydrodynamic force and working state of Francis turbine.(c) The characteristics of flow field in draft tube vortex tape are presented along with relationship between amplitude and frequency about the pressure fluctuation near ring gate. And the reason for pressure fluctuation is given according to the characteristics of flow field in draft tube. In addition the influence of cavitation coefficient and outlet flow field on stability of ring gate is provided.(d) Mathematic model of six-cylinder synchorous control system is obtained with overturning momentum and axial force model by means of CFD. The controller with use of QFT satisfies the need for trace ablity, robust stability and input disturbance restraint ability, which gets over the uncertain, non-linear and time-variable factors.(e) It shows that QFT control strategy can solve the problem of synchronization and velocity, which keeps from unfavorable influence of non-linear and uncertain factors.(f) The reliability of synchorous system and axial force of cylinders by numerical simulation are verified by engineering applications of Nansha Hydropower Station on Honghe River.