Analysis Of Solid-liquid Two-phase Flow And Runaway Characteristics Of Francis Turbine Based On CFD

With the gradual increase of energy consumption,hydropower as a cleaning energy has an increasingly important position,hydropower stations play an important role in peak and frequency modulation.However,due to the increase of soil erosion in recent years,most of the power stations is operating under the rivers with more sediment in China.As a result,the turbines operating under this situation are prone to suffer the problem of abrasion of sediment particles and disrupt the hydraulic turbine blades,which reduced the life of the turbine,and brought the great harm to the power plant.In this paper,the numerical simulation of the turbine running in situation of solid-liquid two-phase flow was carried out to reveal the flow law of the solid particles in turbine and to analyze the wear in the over-flow parts.Another serious problem encountered in the operation of the turbine is the generation of the runaway condition due to the rejection of the gate opening mechanism when the turbine under load rejection.The flow characteristics of the turbine under runaway condition were studied.In view of the above problems,the research contents and work are as following:⑴The CAD and SolidWORKS software were used to establish the turbine runner model with the HL240 turbine wooden patterns.And the over flow parts including spiral casing,guide vane,draft tube were designed by hydraulic calculation.Finally,the ICEM CFD and Turbogrid software were used to divide the structured and unstructured grid according to the different structure of the turbine.⑵The Particle model and inhomogeneous model in CFX were introduced to simulate the solid-liquid two phase flow in the turbine.The guide vane opening was 24°,and 16 small operating conditions in total were selected in different densities,diameter and concentration in this study.The outer characteristics of the turbine under the solid-liquid two-phase flow are obtained.The wear and flow characteristics of the internal solid phase of the over-flow components,including spiral casing,guide vanes and runner blades,were analyzed,the result of the simulation was compared with the experimental result in reference,it shows good agreement with the actual operating condition.⑶In the study of the runaway condition,the steady-state conditions calculated at six different opening degrees are used as the initial conditions,combined with the control equation in runner under the runaway condition to simulate the dynamic characteristics of the turbine in the runaway condition.The result shows that at the runaway operating condition,the flow velocity increased rapidly,the vortex was appeared in the runner in different degree.From the pressure distribution of the runner blade,the blade pressure rises sharply in the runaway condition,and the high pressure is concentrated near the shroud of the blade.The internal flow and the positive pressure distribution of the narrow high draft tube are analyzed,and the internal flow lines of draft tube was compared with before and after the runaway condition.