混流式水轮机叶道涡演化及压力脉动特性研究

Investigation of Inter-blade Vortex Evolution and Pressure Fluctuation Characteristic for Francis Turbine

水—风—光互补发电系统中的水轮机将由主要担任发电任务的常规水轮机逐渐转变为担任调节负荷任务的调能水轮机,其运行在部分负荷工况诱发的叶道涡严重制约着水轮机的运行稳定性。本文基于SST k-ω湍流模型与Zwart空化模型耦合的方法开展了混流式水轮机部分负荷工况下叶道涡不稳定流动特性研究。结果表明,转轮上冠处的流动分离对叶道涡的形成有重要贡献。叶道涡在转轮内为一个强度周期性改变的动态过程,其脉动主频为转频的1.1倍。叶道涡强度的变化可分为涡结构由展向中间位置向出水边迅速发展形成完整叶道涡和完整叶道涡强度缓慢增加的两个过程。叶道涡的动态演化会显著增强转轮叶片吸力面出水边一侧的压力脉动幅值,直接影响水轮机的水力稳定性。

Operating stability of the hydraulic turbine is seriously restricted by the inter-blade vortex induced at partial loads due to role transition of the turbine from the conventional turbine which is mainly used to generate power to the power regulating turbine which is used for regulating load in the water-wind-light complementary power generation system.In this paper,the SST k–ωturbulence model and the Zwart cavitation model are used to numerically investigate the unsteady flow characteristics of the inter-blade vortex in Francis turbine.The numerical results show that the flow separation on the runner hub plays a decisive role on the formation of the inter-blade vortex.The evolution of inter-blade vortex is characterized by a dynamic process with periodic intensity changes in the runner,and the domain frequency of the inter-blade vortex pulsation is 1.1 times of the rotating frequency.The variation of vortex strength can be divided into the first stage featuring the rapid formation process of complete vortex structure from the middle position to the trailing edge of the runner blade along the spanwise and the second stage where the intensity of the inter-blade vortex is gradually increased with the same appearance.The pressure fluctuation amplitude on the trailing edge of the runner baled suction side is significantly magnified by the evolution of the vortex structure,which cause several adverse effects on the hydraulic stability.