Particle image velocimetry measurements have been carried out in a low-pressure turbine cascade operating under unsteady inflow to deeply investigate reduced frequency and flow coefficient effects on flow dynamics, and, consequently, on loss generation in the boundary layer and in the core flow region. Two independent measuring setups have been used for the purpose. The first one captured a large view of the entire blade passage, thus allowing the observation of the incoming wakes and related large-scale vortices developing in the core flow region. The second setup was instead focused on the rear part of the blade suction side to analyze the boundary layer development and to observe the mechanisms dominating the wake–boundary- layer interaction. Tests were performed for four flow cases, varying the reduced frequency and the flow coefficient independently. Proper orthogonal decomposition has been applied to quantify the turbulent kinetic energy production in the core flow, due to wake dilatation and distortion, and in the boundary-layer region. Upstream wake migration and boundary-layer-related losses are consequently quantified from particle image velocimetry data and compared with total pressure measurements for the different combinations of the inflow parameters, providing a clear view of the different loss sources affecting the unsteady operation of low-pressure turbine cascades.

在不稳定流入下运行的低压涡轮叶栅中进行了粒子图像测速测量，以深入研究频率和流量系数对流动动力学的影响，从而对边界层和核心流动区域中的损失产生进行深入研究。为此使用了两个独立的测量装置。第一个捕获了整个叶片通道的大视图，从而可以观察到进入的尾流和在核心流动区域中形成的相关大型涡流。相反，第二个设置集中在叶片吸力侧的后部，以分析边界层的发展并观察主导尾流-边界层相互作用的机制。对四种流量情况进行了测试，独立地改变降低的频率和流量系数。适当的正交分解已被应用于量化核心流中由于尾流膨胀和变形以及边界层区域中的湍流动能产生。因此，从粒子图像测速数据中量化上游尾流迁移和与边界层相关的损失，并与不同流入参数组合的总压力测量值进行比较，从而清楚地了解影响低压不稳定运行的不同损失源涡轮叶栅。