冲击式水轮机喷射机构优选与磨损特性分析

Optimization and Analysis of Erosion Characteristics of Injector for Pelton Turbine

为探索冲击式水轮机喷射机构水力性能和泥沙磨损特性,以500 MW冲击式水轮机为例,结合VOF模型和离散项模型对喷射机构内水气沙三相流进行了数值计算,求解得出不同喷针/喷嘴锥角喷射机构效率和流量,得到了喷射机构在不同开度下的流动特性和泥沙磨损特性,并结合实际电站磨损情况进行对比分析。结果表明:喷针/喷嘴锥角为45°/62°组合的喷射机构具有更好的调节性能。在额定开度下,喷射机构的水力效率达98.5%,比小容量机组的效率略高,随着开度的减小,效率有所下降。支撑肋导致喷射机构内形成附着涡并向出口发展,使颗粒撞击速度增加,从而对喷针表面造成不对称磨损,喷嘴磨损主要发生在出口边附近。附着涡致使速度场分布不均,导致喷嘴出口处水流卷吸空气形成了漩涡,致使泥沙颗粒发生“逃逸”现象。研究成果可为冲击式水轮机的设计和运行提供参考。

Pelton turbines are often deployed in high-head areas of sediment laden rivers.The high-speed flow carrying sediment passes through the unit,causing erosion on the injector and buckets.For the purpose of exploring the hydraulic performance and sediment erosion characteristics of the injector for Pelton turbines,this paper numerically simulates the water-air-sediment flow in the injector for 500 MW Pelton turbine based on the VOF model and DPM model.The hydraulic efficiency and flow rate of the injector with different needle/nozzle angles are solved,the flow pattern and erosion characteristics of the injector under different openings are obtained,which are compared with the real hydropower plant.The results show that the control performance of the injector with 45°/62°angle combination is better than that with 54°/80°and 60°/90°angle combination.Under the design condition,the hydraulic efficiency reaches 98.5%,which is slightly higher than that of small capacity units.High efficiency can be maintained in the range of 60%~100%opening,and the efficiency decreases rapidly when the opening is less than 60%.As the opening decreases,the velocity gradient near the outlet rises and the jet diameter shrinks,there is a high-pressure zone at the tip of the needle and a“velocity deficit”zone at the center of the water jet.Meanwhile,three kinds of vortices in the injector and water jet are analyzed.The supporting ribs lead to the formation of attached vortex in the injector.Furthermore,this vortex accelerates the particle and results in asymmetrical erosion on the needle surface.The attached vortex at the outlet induces the uneven distribution of velocity and generates the air vortex which makes sediment particles escape.Besides,the friction between the surface of water jet and air causes the vortex of surrounding air and consumes the energy of water jet.This paper can provide references for the design and operation of large capacity Pelton turbines.