Unsteady flow and fluid-structure interactions in turbines with full- and partial admission

随着可再生能源使用的不断增加，对汽轮机的灵活性和部分负荷运行提出了更高的要求。利用控制级，可以实现汽轮机的高效部分负荷运行。在控制阶段的部分负荷进气过程中，进气段和非进气段之间出现了较大的速度梯度和压力梯度，这是造成非定常流动状态和转子叶片强循环应力的原因。在公开的文献中可以找到这些复杂的流体和结构力学现象的非常有限的实验研究。部分承认的涡轮的数值研究是提高对这些现象的物理理解的适当工具。然而，使用实验验证数值代码是必要的，但由于可用的实验数据库较差而受到限制。在本项目中，将对大型轴向空气涡轮进行详细的实验研究。计划将流动研究与激光光学测量系统、流道内和侧壁处的时间分辨测量以及转子叶片上的非定常剖面压力测量相结合。基于这些详细的流动测量，流动条件将以高时间和空间分辨率描述。结合实验首次获得了部分进气道对控制级来流场的影响、与叶片流道内流场的相互作用以及叶片的时间分辨结构-力学激励。此外，将使用商业ranss求解器进行瞬态三维cfd模拟，并通过实验进行验证。数值结果将深入了解流动的细节，这些细节分别无法通过实验或过多的努力获得。此外，为了提高对物理的理解，并检查这些发现在其他机器上的应用，还计划进行补充参数变化。通过流体力学/结构力学的耦合研究，将研究部分进气引起的转子叶片的激励。这些研究的目的是提高对三维时间分辨流动现象的物理认识，以及由于汽轮机部分进气引起的流固相互作用。未来，该项目的结果将有助于改进蒸汽轮机的设计过程，以提高操作灵活性和部分负荷运行效率，这是下一代涡轮机所必需的。

Due to the increasing use of renewable energy sources, higher demands on the flexibility and part-load operation of steam turbines arise. Using a control stage, an efficient part-load operation of steam turbines can be realised. During part-load admission of the control stage, high velocity and pressure gradients between admitted and not admitted sections appear, which are responsible for unsteady flow conditions and a strong cyclic stress of the rotor blades. Very limited experimental investigations of these complex fluid- and structure-mechanical phenomena can be found in open literature. Numerical investigations of partial-admitted turbines are an appropriate tool for improving the physical understanding of these phenomena. However, a validation of the numerical codes using experiments is necessary, but restricted due the poor experimental data base available. In this project detailed experimental investigations in a large-scale axial air turbine will be performed. It is planned to combine flow investigations with a laser-optical measurement system, time-resolved measurements within the flow channel and at the sidewalls as well as measurements of the unsteady profile pressures on the rotor blades. Based on these detailed flow measurements the flow conditions will be described with high temporal and spatial resolution. For the first time, the influence of partial admission on the incoming flow field of the control stage, the interaction with the flow field within the blade passages as well as the time-resolved structure-mechanical excitation of the blades can be captured with combined experiment.In addition, transient 3D CFD-simulation using a commercial RANS-solver will be carried out and validated with the experiments. The numerical results will gain insight into flow details, which cannot be captured by the experiments or with too much effort, respectively. Further on, supplementary parameter variations are planned in order to improve the physical understanding and to check the application of the findings to other machines. By coupled fluid-mechanical / structural-mechanical investigations the excitation of the rotor blades due to the partial admission will be investigated.Aim of these investigations is to improve the physical understanding of the 3D time-resolved flow phenomena as well as fluid-structural interactions due to partial admission in steam turbines. In future, the results of this project will contribute to an improved design process of steam turbines for higher operational flexibility and improved efficiency for part-load operation, necessary for forthcoming generations of these turbomachines.