Francis Turbine Whole Flow Passage Of The Internal Flow Field Numerical Simulation

As a core component of a hydropower station,hydraulic turbine plays a vital role in the integration of a station.Research on the technology of hydraulic turbine is continuously increasing with the development of water electricity.However,in many domestic and foreign hydropower stations,due to some technical problems,the malfunction of the water-turbine generator set still exist,which may lead to the damage of flowing parts.The efficient and steady performance of Francis turbine has been taken into more consideration with its increase in capacity,size and speed.It is essential to do further research on the internal flow field simulation.Therefore,studies of steady and unsteady flow in hydraulic turbine components are of importance to deeply understand the hydraulic turbine vibrating intrinsic mechanism, improve the comprehensive hydraulic performance of the hydraulic turbine,and enhance the operating stability of the water-turbine generator set.CFD(Computational Fluid Dynamics)technology has the characteristics of flexibility,short-term design,low cost,and so on.This technology provides researchers with a new and effective research method. Accurate simulation of the steady and unsteady flow field in the hydraulic machinery will help us to analyze the performance of different components.CFD technology is becoming an essential tool for researching the energy performance and the hydraulic stability of the Francis turbine.Mathematic model and computational technology could be applied to conduct the flow simulation and computation of the whole passage in the hydraulic turbine,which is the feasible research method and trend of hydraulic turbine flow computation.Without considering the interaction of the components,the predicted result of CFD simulation based on the single flow passage or single flow component in hydraulic turbine showed a great deviation.Therefore,the simulation in whole passage is necessary.Based on the parameters of prototype Francis turbine in a hydropower station,this research established a geometric and physical model for full flowing passage of the hydraulic turbine.3D numerical simulation and analysis of interior flow characteristics through a Francis turbine were conducted on the basis of 3D N-S equations.Firstly,the numerical simulation of complete components and coupled rotorstator steady turbulence flow was conducted by standardκ—εturbulence model under different operational conditions.The flow information in the Francis turbine was obtained.The efficiency and cavitation performance were quantifiably analyzed and forecasted.Based on the steady turbulent flow simulation,the unsteady numerical simulation of rotor-stator interaction was conducted by RNGκ—εturbulence model and sliding mesh technology.The calculation results were closer to the actual distribution of the flow field.Large Eddy Simulation method was also tried and used in the research.The results showed that the hydraulic turbine flow was the turbulent flow in complex state.The internal flow passage within runner was filled with cross-flow and back-flow,and so on.The entire flow passage was full of various vortices,including blade channel vortex,Kármán vortex,and draft tube vortex.They had a.huge impact on the efficiency and stability of the turbine.Boundary conditions of whole passage simulation could be given more easily,compared with single component simulation.Calculation results were closer to those of the real situation.The simulation in the whole passage can make more accurate prediction of the performance.