混流式水轮机启动过程中流场相干结构分析

Coherent structure analysis of Francis turbine during start-up

为研究混流式水轮机启动过程中转轮区及尾水管流场特征,利用数值模拟方法,开展了混流式水轮机的全流道非定常数值研究,揭示了混流式水轮机在不同工况下启动过程中叶轮区的速度特征与流场中瞬态变化的流动特性。研究表明:额定工况下水轮机的导叶区流速沿流道均匀增大且平缓无冲击,蜗壳流道内无明显分离或涡流。启动过程中水流相对速度方向与转轮区内流动方向不一致,尾水管的相干结构最初为大尺度涡结构,随着水流冲击载荷的增大逐步将刚形成不久的大尺度涡结构冲散,随后将边缘的小尺度涡整合形成细长而稳定的涡带结构。研究结论有助于更好地了解混流式水轮机启动过程中的内流动演变特征以及尾水管的涡带特征。

In order to study the flow field characteristics of runner area and draft tube during the start-up of Francis turbines,we use the numerical simulation method to carry out the unsteady numerical study on the whole flow channel of a Francis turbine,and reveal the speed characteristics of impeller and the transient flow characteristics in the flow field during the start-up of the Francis turbine under different working conditions.The research show that the flow velocity in the guide vane area of the turbine increases uniformly and smoothly without impacting along the flow channel under rated working conditions,and there is no obvious separation or vortex in the volute flow channel.However,during the start-up process,the relative velocity direction of the water flow is in consistent with the flow direction in the runner area.The coherent structure of the draft tube is initially a large-scale vortex structure.With the increasing impact load of the water flow,the newly formed large-scale vortex structure is gradually dispersed,and then the small-scale vortex at the edge is integrated to form a slender and stable vortex rope structure.The research results can help to better understand the evolution characteristics of internal flow and the vortex characteristics of draft tube during the start-up of Francis turbines.