Abstract Internal serpentine ribbed coolant channel with low aspect ratio (AR) has been widely employed to provide excellent thermal protection for advanced first-stage turbine blades. Various height differences ( ΔH s) of adjacent passages along pressure side can be generated under the restriction of actual blade profile. The present work made an attempt to acquire detailed influences of ΔH on the time-averaged and transient secondary motions near sharp bends of low-AR coolant channels. An actual blade ribbed three-pass coolant channel with two ΔH s was chosen as experimental model. Planar time-resolved particle image velocimetry technique was applied to capture the transient flow fields in 21 typical cross sections. Time-averaged results were validated by standard PIV measurements and flow visualizations. Snapshot proper orthogonal decomposition was employed to extract the dominant flow structures and identify the underlying small-scale flow patterns in time-resolved velocity fields. The experimental results indicated the low-AR channel with real blade profile induces a new type of the secondary-vortex superposition downstream of bends, in comparison with the large-AR channels in open literature. The crucial reason is the ΔH along pressure side leads to an intensive impingement on the bend wall, which weakens the effects of bend, rib and curvature of suction side. Another new discovery is the effect of ΔH on unsteady internal flow. In the small ΔH case, the oscillatory frequency of the secondary vortices is nearly similar with the counter-rotating Dean-vortices; however, in the large ΔH case, the oscillatory frequency is much lower, and the rotating direction of vortices is same and unchanged in a period. Increasing inlet Reynolds number can significantly change the underlying small-scale flow patterns and improve the oscillatory frequency of large-scale structures, although the basic time-averaged flow patterns are nearly same. Effect of injection from auxiliary-hole (AH) on unsteady internal flow is obvious and the optimum mass flow ratio of AH-to-inlet is 5%. Graphic Abstract

中文翻译：

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低纵横比现实叶片蛇形冷却剂通道中通道布局对非定常内部流动影响的 POD 分析

摘要 具有低纵横比（AR）的内部蛇形肋冷却剂通道已被广泛用于为先进的一级涡轮叶片提供良好的热保护。在实际叶片型面的限制下，沿压力侧的相邻通道会产生各种高度差（ΔH s）。目前的工作试图获得 ΔH 对低 AR 冷却剂通道急弯附近的时间平均和瞬态二次运动的详细影响。选择具有两个 ΔH s 的实际叶片肋状三通道冷却剂通道作为实验模型。应用平面时间分辨粒子图像测速技术来捕获 21 个典型横截面的瞬态流场。时间平均结果通过标准 PIV 测量和流量可视化进行验证。使用快照适当的正交分解来提取主要流动结构并识别时间分辨速度场中的潜在小规模流动模式。实验结果表明，与公开文献中的大 AR 通道相比，具有真实叶片轮廓的低 AR 通道在弯曲下游诱导了一种新型的二次涡叠加。其关键原因是沿压力侧的ΔH导致对弯壁的强烈冲击，削弱了弯曲、肋和吸力侧曲率的影响。另一个新发现是 ΔH 对非定常内部流动的影响。在小 ΔH 的情况下，次级涡旋的振荡频率与反向旋转的迪安涡旋几乎相似；然而，在大 ΔH 的情况下，振荡频率要低得多，并且在一个周期内，漩涡的旋转方向相同且不变。增加入口雷诺数可以显着改变潜在的小尺度流动模式并提高大型结构的振荡频率，尽管基本的时间平均流动模式几乎相同。副孔（AH）注入对非定常内流影响明显，AH与入口的最佳质量流量比为5%。图形摘要 副孔（AH）注入对非定常内流影响明显，AH与入口的最佳质量流量比为5%。图形摘要 副孔（AH）注入对非定常内流影响明显，AH与入口的最佳质量流量比为5%。图形摘要