混流式水轮机小开度区工况转换过程瞬态流特性分析

Analysis of Transient Flow Characteristics of Francis Turbine during Transition Process in Small Opening Condition

随着风-光-水多能互补发电的发展,水轮发电机组面临全工况运行调能的挑战。水轮机作为水电机组的核心部件,必将频繁进行工况转换以平衡电网波动,典型的工况转换包括减负荷和启停机等。该文基于动网格技术对调能混流式水轮机小开度区变负荷过程进行了数值模拟计算,分析水轮机组全流道变负荷过程内部流态、转轮进出口环量、叶片正背面压力载荷及压力脉动特性。结果表明:转轮流道内出现的叶道涡结构,主要发生在叶片吸力面进水边位置,随着流量的减小,叶道涡的位置由转轮吸力面靠近进口大约1/4处,逐渐向转轮进口和流道中间移动;转轮出口处的压力逐渐降低,表明随着负荷的进一步减小,转轮流道内的流动更加不稳定。变负荷过程中,转轮进口上冠位置环量值上升较为明显,此处与叶道涡位置基本对应,表明叶道涡在转轮内的动态演变会直接影响转轮进出口的环量分布;叶道涡会引起叶片进口至出口压力载荷分布不均匀,越靠近叶道涡结构位置,压力载荷变化越明显;对转轮叶片表面压力测点进行了信号时域分析,叶片进水边上冠位置测点与出水边下环位置测点处均出现较为明显的涡流结构,且压力幅值较高,表明不稳定涡流结构的出现诱发了转轮内高幅值压力脉动现象的发生。

With the development of wind-solar-hydro multi-energy complementary power generation,hydro-generator units are facing the challenge of energy regulation under full operating conditions.As the core component of hydropower units,the hydraulic turbines undergo frequent operational transitions to balance the fluctuations in the power grid.Typical operational transitions include load reduction and start-stop processes.In this paper,based on the dynamic mesh technology,the CFD numerical simulation of the variable load process in the small opening area of the energy regulating Francis turbine is carried out.The internal flow pattern,the circulation of the runner inlet and outlet,the pressure load and the pressure fluctuation characteristics of the blade are analyzed.The results show that the inter-blade vortex appears in the runner channel,which mainly occurs at the leading edge of the blade suction surface.During the whole variable load transition process,the inter-blade vortex gradually moves from approximately 1/4 of the distance from the leading edge on the suction side towards the turbine inlet and the middle of the flow passage.Additionally,it is observed that the pressure at the turbine outlet gradually decreases,indicating increased flow instability within the turbine flow passage as the load further decreases.During the whole process of variable load,there is a significant increase in the circulation value at the runner crown position of the runner inlet,which corresponds to the position of inter-blade vortex.This suggests that the dynamic evolution of the inter-blade vortex within the runner directly affect the circulation distribution at the runner inlet and outlet.The inter-blade vortex causes uneven distribution of pressure load from blade inlet to the outlet,with more pronounced changes in pressure loads closer to the position of the inter-blade vortex.The signal time domain analysis is performed on pressure measurement points on the turbine blade surface,revealing distinct vortex structures with higher pressure amplitudes at the measurement points near the runner crown position on the blade inlet and the runner band position on the blade outlet.This indicates that the occurrence of unstable vortex structures induces high-amplitude pressure pulsations within the turbine.