The tip flows in modern gas turbines are primarily transonic under realistic conditions and significantly impact the overall thrust performance and safety of the turbines. This study is aimed at providing a deeper understanding of the mechanisms underlying and controlling the tip flow characteristics. Particle image velocimetry (PIV) and Schlieren and oil flow visualizations were performed to reveal the basic structure of the tip flow fields. A computational fluid dynamics model was developed, and the experimental results validated its accuracy. FLUENT 18.0 was employed to apply the Spalart-Allmaras turbulence model and perform two-dimensional calculations that furthered the investigation. The PIV and Schlieren visualization results indicated that the tip flow accelerated rapidly to the transonic level at the gap inlet separation when the gap pressure ratio exceeded 2.0. Furthermore, an oblique shock wave was generated when the transonic tip flow reattached and then reflected within the gap. The oil flow visualization provided the corresponding boundary layer behavior on the bottom wall. Additionally, the computation of the transonic tip flow with respect to various sizes and pressure values demonstrated that the Reynolds number is the key parameter that controls the gap flow field. The flow similarity existed as long as the Reynolds number remained constant. An in-depth analysis of the simulation improved the model performance at predicting the inlet separation size, discharge coefficient, and friction coefficient based on the Reynolds number. The study results provide a reference for the design and testing of engine blade gaps in real-world conditions.

中文翻译：

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雷诺数对跨音速尖端流动的影响

在现实条件下，现代燃气轮机的叶尖流动主要是跨音速的，并且极大地影响了涡轮的整体推力性能和安全性。这项研究旨在更深入地了解和控制叶尖流动特性的机理。进行了颗粒图像测速（PIV）以及Schlieren和油流可视化，以揭示尖端流场的基本结构。建立了计算流体动力学模型，实验结果验证了其准确性。FLUENT 18.0用于应用Spalart-Allmaras湍流模型并进行二维计算以进一步研究。PIV和Schlieren的可视化结果表明，当间隙压力比超过2.0时，在间隙入口分离处，尖端流动迅速加速到跨音速。此外，当跨音速尖端流重新附着并在间隙内反射时，会产生倾斜冲击波。油流可视化在底壁上提供了相应的边界层行为。此外，跨音速叶尖流量相对于各种尺寸和压力值的计算表明，雷诺数是控制间隙流场的关键参数。只要雷诺数保持恒定，就存在流动相似性。对仿真的深入分析提高了模型在预测入口分离尺寸，排放系数，和摩擦系数基于雷诺数。研究结果为实际条件下发动机叶片间隙的设计和测试提供了参考。