Study And Analysis On The Stress And Improve Measures Of Francis Turbine Runner

With the capacity and size of mixed flow hydraulic unit constantly improve, stainless steel blade relatively thinning, runner relative stiffness decreased somewhat, and hydraulic unit running condition complex, result in produced high stress at unction of outlet edge of blade and runner crown, that is important factors caused by runner cracks, that seriously affect hydraulic unit safe and steady operation. In order to improve runner stress distribution achieve the goal of reducing blade cracks. For a certain power station runner cracks which frequently produced closely to outlet edge of runner blade and runner crown, the paper through installing Triangular piecess at the junction of outlet edge of blade and runner crown. now, set side of the side of Triangular, and analysis different dimension triangular pieces’ effect to runner stress and flow field. The paper main research contain the following content:First, ensure the triangular piece L1 edge (triangular piece and blade edge joint edge) and L2 edge (triangular piece and the crown join edge ) meet the condition of L1=L2, the constant flow numerical simulation of full flow passage of hydraulic turbine is carried out under rated water head, rated output condition and maximum head rated output condition. The results show that the stress of the runner decreases with the increase of the size of the triangular piece, and the maximum stress is shifted to the corner at the water outlet of the blade and the water outlet of the triangular block in the two conditions.Secondly, set optimal size of triangular piece as basic size which further improve runner stress, when triangular piece L2 keeps invariant and increase L1,calculated two condition runner stress. The results show that runner maximum stress will decrease with L1 edge increased. Comprehensively compared installing different size triangular piece’s effect on different performance of hydraulic turbine. Triangular pieces size L1/L2=2, that L2 is about 5.7%of runner diameter D1, about 10% of runner blade outlet, about 18% of intersection between front of blade and runner crown. Triangular pieces have little effect on output, efficiency and deformation of hydraulic turbine; The maximum stress of runner only by 40% of original runner.Then, according to the vibration problem of a unit of the Hydropower Station under partial load condition, the stress condition of the runner with the optimum size is calculated. The results show that the triangle block can reduce the maximum stress of the runner in part load,which indicates that the stress distribution of the runner can be improved under different conditions of the turbine.As for runner which was installed best Triangular pieces, running unsteady numerical simulation, study to find the pressure fluctuation frequency of basin of runner and draft tube was not affected by Triangular pieces, the pressure fluctuation amplitude variation within 3%.