空化动水对水轮机转轮附加质量和振动特性的影响机理研究

As a common phenomenon in hydro machinery, cavitation is generally considered as an important exciting source to cause runner vibration. However, cavitation significantly impacts on the added mass and natural frequencies of the hydrofoil in the latest test. While this effect is generally neglected for hydro turbines. It is required more in-depth studies on hydroturbine dynamic characteristics in cavitating flowing water. Therefore, it is important to strengthen the theory and technical research on FSI problem of runners under flowing water. Structural FSI dynamic response model is setup and the vibration modal parameter identification method is proposed to study the dynamic characteristics of the structure by mean of theoretical analysis, algorithm research and numerical simulation in this proposal. The numerical platform of structural vibration modal parameter identification in cavitating flowing water is established to study natural frequencies and damping ratio of the runner under 3D full passages. The effect of viscosity, velocity, pressure and cavitation to added mass and added damping of the runner is also checked. Research results will help to reveal the effect mechanism of cavitation evolution to runner dynamic characteristics, and comprehensively understand the migration of natural frequencies and damping ratio of the runner, as well as providing theory and technical support to the design and safe operation of hydropower units.

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。最新试验发现空化对翼型附加质量和固有频率影响很大，然而这种影响在水轮机转轮中常被忽略，这就要求对水轮机转轮在空化动水条件下的动态特性进行深入分析。因此，需要加强转轮在空化流动状态下结构流固耦合问题的相关理论和技术研究。本项目拟通过理论分析、算法研究和数值模拟，建立结构流固耦合动态响应模型，提出基于振动参数识别方法和双向流固耦合技术的空化动水中结构模态参数识别算法，构建空化动水条件下结构振动参数模态识别的数值计算平台，应用该平台研究三维全流道水轮机转轮的固有频率、阻尼比等动态特性；分析粘度、速度、压力等流场参数和空化状态对转轮振动特性的影响。研究成果将有助于揭示空化演变对转轮固有频率衰减率及等效阻尼比的影响机理，深入理解转轮动态特性随空化演变的迁移规律，为水电站机组设计和安全运行提供理论依据和技术支撑。

最新研究发现，空化会导致转轮的动力特性发生改变，给机组的安全稳定运行造成了一定的隐患，而对转轮在空化条件下的动力特性的研究还在起步阶段。本研究以理论分析、算法研究、数值模拟为手段，发展了基于振动参数识别的模态分析(VTMDI)方法，该方法可以分析结构在复杂流动条件下特别是空化条件下的振动特性，并可以隐式求解得到结构在水中的自然频率和等效阻尼比。通过基于NACA0009翼型的数值与实验对比，验证了流固耦合模态算法的可靠性，计算结果发现随着水中汽液体积分数的变化，结构的各阶模态可以相互转换，提出了“模态转捩曲线”来描述这种变化规律。通过预测水泵水轮机转轮在不同空化发展程度下湿模态的变化规律，揭示了空化演变对转轮固有频率衰减率等振动特性的影响机理，评估了机组的振动特性。研究成果有望促进大型水力机械转轮复杂工况下的模态分析基础理论研究。