多工况下混流式水轮机的应力特性试验研究

Experimental study on stress characteristics of Francis turbines under multiple operating conditions

摘要

【目的】为深入研究水轮机转轮叶片在复杂运行工况下的动态受力特性与疲劳损伤机制【方法】基于现场试验数据，采用傅里叶变换(FT)技术，对混流式水轮机转轮叶片关键部位(如叶片根部、出水边)的应力信号进行了时频域分析，系统考察了变负荷、空载及启停机瞬态过程中叶片关键部位的应力响应特征。【结果】结果显示：在变负荷工况下，测点7FSG12和13FSG1最大静应力分别达到27.56 MPa、25.99 MPa,测点13FSG2和13FSG14最大动应力分别为13.19 MPa、13.04 MPa,且叶片与下环交界处动应力分布呈现从进水边向出水边递减的趋势，具体表现为7FSG10> 7FSG8> 7FSG6;在320 MW工况下，大部分测点动静应力均低于290 MW和300 MW工况。【结论】结果表明：转轮叶片与上冠链接区域(特别是靠近出水边位置)存在显著的应力集中现象，与实际裂纹萌生区高度吻合，建议增设减应力三角块以改善应力分布；动静干涉效应的影响强度随距无叶区距离的增大而减弱；机组在320 MW超额定出力状态下，具备短期安全超发能力。然而需注意，在启停机及空载工况下，叶片承受的交变应力幅值显著高于变负荷工况，其疲劳损伤风险随启停频次急剧增加。因此，为提升水力机组的结构可靠性与运行安全性，建议优化机组运行策略，尽量减少非必要的启停操作次数。

Abstract

[Objective] The study aims to investigate the dynamic stress characteristics and fatigue damage mechanisms of turbine runner blades under complex operating conditions. [Methods] Based on field test data, Fourier transform(FT) technology was used to perform time-domain and frequency-domain analysis of stress signals at key parts(such as blade root and outlet edge) of the Francis turbine runner. The stress response characteristics of these key parts of blades were systematically investigated during variable load, no-load, and start-stop transient processes. [Results] The result showed that under variable load conditions, the maximum static stresses at measurement points 7FSG12 and 13FSG1 reached 27.56 MPa and 25.99 MPa, respectively, while the maximum dynamic stresses at measurement points 13FSG2 and 13FSG14 were 13.19 MPa and 13.04 MPa, respectively. Furthermore, the dynamic stress distribution at the junction of the blade and the lower ring showed a decreasing trend from the inlet edge to the outlet edge, specifically manifested as 7FSG10 > 7FSG8 > 7FSG6. Under the 320 MW condition, the dynamic and static stresses at most measurement points were lower than those under the 290 MW and 300 MW conditions. [Conclusion] The result show that significant stress concentration is observed in the connection zone between the runner blade and the upper crown(especially near the outlet edge), which is highly consistent with the actual crack initiation zone. It is recommended to add a stress-reduction triangular block to improve stress distribution. The intensity of the rotor-stator interaction effect decreases with increasing distance from the blade-free zone. The unit is capable of short-term safe power overgeneration under the condition of 320 MW over-rated output. However, it should be noted that the alternating stress amplitude on the blade under start-stop and no-load conditions is significantly higher than that under variable load conditions, and the fatigue damage risk increases sharply with the frequency of start-stop cycles. Therefore, to improve the structural reliability and operational safety of hydraulic units, it is recommended to optimize the operational strategies to minimize unnecessary start-stop operations.

关键词

混流式水轮机 / 转轮应力 / 疲劳裂纹 / 时频域分析 / 现场测试 / 动静干涉 / 转轮叶片 / 影响因素

Key words

francis turbine / runner blade stress / fatigue crack / time-frequency domain analysis / field test / rotor-stator interaction / runner blade / influencing factor

基金资助

国家自然基金项目(52309111)

中国水科院基本科研专项(HM110145B0012023)