Frequency and vibration amplitude prediction of rotating discs subject to mode splitting

现代水电涡轮机的设计是为了达到近乎完美的效率，同时保持生产成本尽可能低。实现这一目标的一种方法是通过减小涡轮机叶片的厚度，从而降低其刚度并增加其经受临界振动水平的倾向。此外，由于间歇性可再生能源的集成，最终用户对功率调节的需求不断增长，导致更频繁的非设计操作以及机器启动和停止，动态机械应力明显高于最佳效率点。在这种情况下，精确了解涡轮机动态特性，特别是转子固有频率随转速的变化，对于避免问题振动至关重要。在许多出版物中，水泵水轮机转轮使用浸没在水中的旋转圆盘进行建模，突出了频率分裂现象：圆盘旋转时出现向前和向后的行波。这种现象与附加质量随转速的变化有关。该项目有两个主要目标：更好地理解的机制ofturbulence分裂;并制定一个简化的仿真策略，以评估的固有频率的一个turbulingdisk。了解水泵水轮机转轮的频率分裂及其基本机制对于评估产生的应力和机器的预期寿命至关重要。该项目将为高水头弗朗西斯水轮机和水泵水轮机的设计提供一个准确、快速的工具。该工具对于开发新的可靠涡轮机并提供有关设备疲劳寿命的详细信息至关重要。

Modern hydroelectric turbines are designed to achieve near perfect efficiency while keeping production costsas low as possible. One way to accomplish such a goal is by reducing the thickness of turbine blades,consequently lowering their stiffness and increasing their propensity to experience critical vibration levels.Moreover, the end-users' growing need for power regulation due to the integration of intermittent renewablesources leads to more frequent off-design operations as well as machine starts and stops, for which dynamicmechanical stresses are significantly higher than at best efficiency point. In this context, precise knowledge ofthe turbine dynamic characteristics, notably the variation of the natural frequencies of the rotor with rotationrate, is essential to avoid problematic vibrations. In many publications, pump-turbine runners have beenmodelled using a rotating disk submerged in water, highlighting the phenomenon of frequency split: a forwardand a backward travelling waves emerge as the disk rotate. This phenomenon is linked to the variation of addedmass with rotational velocity. The project has two main objectives: understand better the mechanism offrequency split; and develop a simplified simulation strategy to evaluate the natural frequencies of a rotatingdisk. Understanding the frequency split of pump-turbine runners and its underlying mechanisms is critical toevaluate the resulting stresses and the expected life of the machine. This project will provide an accurate andfast tool to improve the design of high head Francis turbines and pump-turbines. This tool is essential todevelop new reliable turbines and provide detailed information about the fatigue life of the equipment.