Numerical Simulation And Analysis Of Solid-liquid Two-phase Flow In Bulb Tubular Turbine

China's hydropower resources are abundant,with the largest installed capacity in the world.Many rivers have high sediment content,and turbines in operation are inevitably subject to sediment wear.The worn turbine has caused problems such as vibration of the turbine set,shortened maintenance intervals,and reduced efficiency.The design phase took a series of measures against these issues,but the effect was not obvious.Compared with Francis turbines,there are fewer research results on the bulb tubular turbine set.For this reason,it is of practical significance and application value to theoretically analyze the performance and the effect of sediment wear of bulb tubular turbine running in sandy water.In this paper,a typical bulb tubular turbine on the main stream of the Yellow River is chosen as the research object,and the rated condition of low head power station is selected during the wet period.First,the unsteady numerical simulation of the whole flow channel under water condition is carried out,and the results are taken as the comparison benchmark for the analysis of solid-liquid two-phase flow.Then,the unsteady numerical simulation of solid-liquid two-phase flow is done to obtain the relationship between the particle diameter,the inlet volume fraction and the wear degree of the flow passage component,and the flow law of the sediment particles in the whole flow channel and the change of the running performance of the hydraulic turbines are analyzed.In view of the above problems,the following research works are done in this paper.(1)According to the two-dimension drawing of bulb tubular turbine,the whole flow channel of bulb tubular turbine is established by using three-dimensional modeling software,which is divided into four parts of the front runner,guide vane,runner and draft tube.In the ICEM CFD,the whole flow channel is divided into structural and unstructured meshes.(2)In the Ansys CFX,the inhomogeneous model and the particle model are used to do the unsteady numerical simulation calculation for the solid-liquid two-phase flow in whole flow channel.According to the two aspects of sediment particle diameter and inlet volume fraction,a total of 9 working conditions are calculated,and the variation law of internal flow field characteristics of the turbine is obtained.The surface abrasion of the bulb body,guide vane,runner and draft tube was analyzed and sediment particle flow analysis was carried out.When the volume fraction of sediment particles is 3.5% and the diameter is increased from 0.15 mm to 0.75 mm,the simulation results show that the larger the diameter of the sediment particles,the more sediment at the bottom of the bulb body,and the inlet edge of guide vanes,the inlet edge of blade,and the bottom of draft tube are worn seriously.When the diameter of the sediment is 0.75 mm and the volume fraction is increased from 1.5% to 5.5%,the most serious wear of the bulb body is the bottom firstly,and then transferred to the outlet.At 5.5%,the inlet edge of the guide vane is badly worn.At 3.5%,the local wear of the inner and outer ring surface of the guide vane is high.The wear degree of the inlet edge and outer edge increases gradually.At 3.5%,the sediment deposition at the bottom of the draft tube is large,and at 5.5%,there is a circumferential distribution of the sediment in the inlet area.(3)Comparison of pure water and sandy water conditions shows that the existence of sediment particles reduces the efficiency of turbines.When the sediment particle diameter increases from 0.15 mm to 0.45 mm,the efficiency drop is greater than 0.45 mm increases to 0.75 mm.The effect of the change of the inlet volume fraction of the sediment particles on the decrease of the efficiency is the opposite,and the decrease of the efficiency of the 1.5% to 3.5% is less than 3.5% to 5.5%.(4)The efficiency test and pressure pulsation test of bulb tubular turbine were made under the sandy water condition.The result of efficiency test is that the efficiency of the turbine decreases with the increase of sediment particle diameter and volume fraction,and the efficiency change and pressure pulsation are more intense with the change of the particle volume fraction,which accords with the change rule of the numerical simulation analysis.