Numerical Simulation Of Solid-liquid Two-phase Flow Of Tubular Turbine Based On Vortex Analysis

China is rich in water resources,and hydropower is an important energy source in China,but many river basins have high sediment content.Hydraulic Turbines will suffer from sand wear during operation.After wear,the turbine will suffer unit vibration,damage to overcurrent components,and reduced efficiency.Problems,which leads to hidden dangers and huge economic losses.Although measures will be taken to address these issues during design,the final effect is not significant.Compared with Francis turbines,there are few laws and theories about the conclusions of the research of tubular turbines.Therefore,it is necessary to research the performance of tubular turbine under solid-liquid two-phase flow conditions,sediment wear and internal flow laws.This paper selects the middle and lower reaches of the Yellow River Basin,where the tubular turbine of a power station that has been operating for many years is the research object.Aiming at the working conditions of low head and silt,numerical simulation is carried out on the two-phase flow conditions of water and solid-liquid flow of the whole flow channel of the unit.The flow analysis of each flow component and the internal flow pattern were analyzed by the vortex identification method in vortex dynamics to obtain the effect of solid-liquid two-phase flow on the operation of the turbine and the particle size,sediment volume concentration and wear of the flow component and the relationship of internal flow.Regarding the above content,this article mainly carried out the following research.(1)Through reading a large number of related literatures,the research ideas were drawn up.According to the prototype data of the tubular turbine of a hydropower station in the middle and lower reaches of the Yellow River,the three-dimensional modeling software UG was used to establish the unit's full flow channel model for the five parts of the inlet section,bulb body,guide vane,runner and draft tube.In ICEM CFD,the structural and unstructured grids are divided into various parts.(2)In ANSYS CFX,the steady-state computation of the clear flow conditions and the unsteady computation of the solid-liquid two-phase flow conditions are performed for the entire flow channel.From the two aspects of different particle size and different volume concentration of sediment,a total of 7 working conditions were computed.From the results,the meridian ssection,bulb body,guide vane,runner and draft tube were analyzed.Three vortex methods in vortex dynamics are embedded in the post-processing,and the vortex dynamics analysis is performed on the runner,guide vane,and draft tube areas.(3)When the sediment volume concentration Cv is 1% and the sediment particle size d increases from 0.01 mm to 0.25 mm.The pressure,sediment volume fraction,and slip speed of the bulb body,guide vane blade,runner blade,draft tube and other components are gradually increasing.The volume fraction of sediment is also gradually increasing,that is,the increase in the particle size of the sediment will lead to the increase in the wear of the overcurrent components.The vortex identification method is applied to the meridian plane,the guide vane area,the runner area and the draft tube area.In these areas,it is found that the vortex strength and the sediment particle size show a weak correlation.(4)When the particle size of the sediment is 0.1mm,the volume concentration increases from 1% to 7%.Bulb body,guide vane blades,runner blades,draft tube and other components pressure and sediment volume fraction are gradually increasing,but the slip speed is decreasing.Using eddy recognition method in each area,it was found that most areas were affected by concentration.As the concentration increases,the Q value and the vorticity value are seen to decrease,but the identified vortex positions are consistent,and the effect is more on the strength of the vortex motion.(5)The comparison between the water condition and the solid-liquid two-phase condition found that the presence of sediment significantly reduced the efficiency of the turbine,and also caused an increase in the pressure of various components and an increase in the strength of the vortex motion,which caused wear and increased hydraulic power loss.Through the research of this paper,the internal flow field analysis and transformation of the tubular turbine actually operating under the solid-liquid two-phase flow conditions,and the vortex analysis method are used to study the tubular solid-liquid two-phase flow.The vortex distribution law in the guide vane and runner area can provide a reference for the hydraulic design of the tubular turbine and provide guidance for operation and maintenance.