Numerical Simulation Of Vortex Rope And Pressure Fluctuation Prediction Inside Francis Turbine Draft Tube

The influence of the Large Francis' s single machine capacity and structure size turbine depends on the development trend of large-scale,so in the stable operation problems of the increasingly prominent.When Francis turbine operating out of design conditions,the swirl of the runner outlet will produce spiral vortex in the draft tube,and the pressure fluctuation caused by vortex is the main reason for instability of hydraulic turbine.So far,the main means to evaluate the hydraulic stability of the turbine is still to carry out the model pressure pulsation test,in the design stage cannot effectively predict control design of hydraulic turbine draft tube vortex band induced by the pressure pulsation.It is an effective way to improve the hydraulic stability of the turbine,how to effectively control the pressure fluctuation caused by vortex in draft tube of turbine in design stage.Therefore,it is necessary to use numerical simulation methods and experimental means,combined with relevant information,for Francis turbine under part load in the mechanism of the formation and development of the turbine draft tube vortex are explored in more depth.Research the relationship between geometric parameters and operating conditions and the draft tube vortex generated of Francis hydro turbine runner.Research prediction calculation method for pressure fluctuation of draft tube vortex,to lay a theoretical foundation for predicting the pressure fluctuation caused by draft tube vortex of Francis turbine at the design stage,and provide a certain theoretical reference for expanding the scope of the non-vortex area as far as possible.Taking one Francis turbine scheme as the research object,explore the motion of draft tube vortex and the characteristics of pressure fluctuation in the numerical simulation.Based on the 3D full channel unsteady turbulent flow simulation,explore the visualization and frequency of draft tube vortex,and prediction and analysis of low frequency pressure fluctuation caused by draft tube vortex.Discussion on the interaction between runner outflow and draft tube,and the relationship between the formation of the vortex and the geometry of the runner and operating conditions.According to the unsteady turbulent flow simulation results in the tail pipe,and carries on the FFT frequency domain transform through to analyze the pressure fluctuation characteristic in the typical working condition of the tail pipe.In this paper,the numerical simulation of the steady and unsteady turbulent flow in the whole flow passage of Large Francis turbine is carried out,to predict and analyze draft tube vortex and the pressure fluctuation caused by it.And it reflects the phenomenon that the generation and the mechanism of pressure fluctuation caused by draft tube vortex.According to the existing research results,lay a theoretical foundation for predicting the pressure fluctuation caused by draft tube vortex of Francis turbine at the design stage,and provide a certain theoretical reference for expanding the scope of the non-vortex area as far as possible.At the same time,the flow field and pressure pulsation of the draft tube can be analyzed in the design process according to a wide range of operating conditions to optimize the flow channel design.And further research on how to use the method in the design process to predict the water pressure fluctuation of the tail pipe to evaluate the hydraulic stability.