空化演变对水轮机转轮固有特性迁移和动应力特性的影响机理研究

The latest studies have found that when cavitation occurs in the runner of hydraulic turbine, in addition to produce a new excitation source and causing vibration and noise increases, it will also have influence on the added mass and added damping of water and vapor in runner as well as runner modal. Thus, the natural characteristics and dynamic stresses of the runner are changed, which will have hidden danger to the safe and stable operation of the unit. It is necessary to analyze the dynamic characteristics of the runner under the cavitation condition. A numerical platform for predicting structural dynamic characteristics in cavitation will be established based on vibration modal parameter identification and the fluid-structure interaction dynamic model with cavitation by means of theoretical analysis, algorithm research, numerical simulation and model test. Then, the results of model tests and numerical simulation will be compared to reveal the influence mechanism of cavitation evolution on vibration characteristics such as natural frequency, modal shape, added mass and added damping. Finally, the influence of the natural characteristics and hydraulic excitation force variation on the dynamic stresses of runner will be qualified; the variation law of runner dynamic characteristics with cavitation evolution will be explored in order to provide the theoretical basis and technical support for the runner design and unit safe operation of hydropower station.

最新研究发现，水轮机组转轮流道内空化发生时，除了会产生新的激励源，引起机组的振动和噪声加大；还会造成转轮内水汽附加质量、附加阻尼和转轮模态的变化，从而导致转轮的固有特性和动应力特性发生改变，给机组的安全稳定运行造成了一定的隐患，亟需对转轮在空化条件下的动力特性进行深入分析。本申请以理论分析、算法研究、数值模拟和模型试验为研究手段，建立含空泡状态的结构流固耦合动态响应模型，基于振动参数识别的结构动力特性算法，构建空化流动条件下结构动力特性变化规律预测的数值分析平台，对比模型试验与数值模拟结果，揭示空化演变（空泡内汽体体积分数、空泡体积、空泡空间位置等的变化）对转轮固有频率、模态振型、附加质量及附加阻尼等振动特性的影响机理。量化转轮固有特性迁移和水力激励力变化对转轮动应力特性的影响，探索转轮动力特性随空化演变的变化规律，为水电站机组转轮设计和安全运行提供理论依据和技术支撑。

空化作为水力机械中的一种常见现象，通常被认为是引起转轮振动的一个重要激励源。最新研究发现，空化还会造成转轮内水汽附加质量、附加阻尼的变化，从而导致转轮的模态和动应力特性发生改变，给机组的安全稳定运行造成了一定的隐患，亟需对转轮在空化条件下的动力特性进行深入分析。本项目以理论分析、算法研究、数值模拟和模型试验为研究手段，发展了旋转状态转轮动力特性水下测试方法并改进了试验装置，建立了含空泡状态的结构流固耦合动态响应模型，构建了空化流动条件下结构动力特性变化规律预测的数值分析平台，量化分析了空化演变对转轮模态和动应力特性的影响。发现严重空化会导致转轮固有频率发生较大变化，并可能引起转轮特定阶次模态共振，造成转轮快速破坏。在轻度空化的情况下，随着空化数的增加，转轮上的动应力均值和幅值会同时增大。而严重空化情况时，随着更多的气泡附着在叶片表面，此时动应力的低频分量会较为明显，其脉动幅值会显著降低。研究成果将有助于深入理解转轮动态特性随空化演变的迁移规律，为水电站机组转轮设计和安全运行提供理论依据和技术支撑。