Unsteady flow and fluid-structure interactions in steam turbine control valves – measures for the stabilization of spherical control valves

随着可再生能源在整体电力供应中所占份额的稳步增长，传统电厂的灵活运行变得越来越重要。在未来，蒸汽轮机将有望提供平衡的动力，这需要一个快速和强大的调节涡轮机。一般来说，短期负载变化可以使用控制阀来实现，而在部分负载条件下延长的时间可能是一个主要挑战。根据阀门设计的不同，在节流条件下的非定常流动条件可能导致流固耦合和剧烈振动，可能导致机械故障。除了更复杂的设计外，球阀作为一种特别易受振动威胁的几何形状仍然被安装在特别是小型汽轮机上。因此，为了确保安全可靠的零件负载运行，良好的流动拓扑知识以及对流动不稳定性的准确预测是必不可少的。为此，实验研究是重要的，但可用的测试数据，特别是弹性设置的汽轮机控制阀是罕见的。在之前DFG项目的基础上，将研究新的几何措施（流动矫直、涡流和湍流产生），用于有针对性地操纵流场和抑制控制阀中的流动不稳定性。在结果的支持下，预期在部分负载下阀门更稳定地运行，同时考虑对现有阀门进行可能的升级。不同的阀门配置将在一个缩放的控制阀上进行实验研究，不仅捕获时间分辨的压力场，而且捕获阀门的动力学。随着声激励的研究，它与流场的相互作用是另一个主要的兴趣。实验研究将伴随着瞬态3D CFD模拟，在与测试数据验证后，将提供对空间流场的详细了解。除了刚性阀外，还将使用耦合流动和结构模拟来评估弹性配置，以便更好地理解激励机制和所研究的几何变化的影响。从中期来看，分析球形调节阀设计中不同的阀门改型以及与声学共振的流动声相互作用，旨在增加汽轮机的灵活性，同时提高部分负荷运行时的效率和流动稳定性。

With a steady growth of the share of renewable energy in the overall power supply, a flexible operation of conventional power plants becomes increasingly important. In the future, steam turbines will be expected to provide balancing power, which requires a fast and robust regulation of the turbine. In general, short-term load changes can be realized using control valves, for which the extended time at part load conditions can represent a major challenge. Depending on the valve design, unsteady flow conditions at throttled conditions can result in fluid-structure interactions with severe vibrations, possibly leading to a mechanical failure. Besides more complex designs, the spherical valve as a particularly vibration endangered geometry is still installed especially in smaller steam turbines. To ensure a secure and reliable part load operation, good knowledge of the flow topologies as well as the accurate prediction of flow instabilities are therefore essential. For that purpose, experimental studies are important but available test data especially for an elastic setup is rare for steam turbine control valves.Based on the outcome of the previous DFG project, new geometric measures (flow-straightening, swirl- and turbulence generation) for a targeted manipulation of the flow field and suppression of flow instabilities in control valves will be investigated. Supported by the results, a more stable operation of valves at part load is intended, also considering possible upgrades for existing valves.Different valve configurations will be investigated experimentally on a scaled control valve, capturing not only the time-resolved pressure field but also the dynamics of the valve. With the examination of acoustic excitations, its interaction with the flow field is another major interest. The experimental studies will be accompanied by transient 3D CFD simulations, which will provide a detailed insight into the spatial flow field after its validation against test data. Besides the stiff valve, the elastic configuration will be assessed using coupled flow and structural simulations enabling a better understanding of the excitation mechanisms and the impact of the investigated geometric variations.In the medium-term, the analysis of different valve modifications and acoustic interactions of the flow with acoustic resonances for a spherical control valve design is intended to increase the flexibility of steam turbines and simultaneously improve efficiency and flow stability at part load operation.