针对旋转叶轮叶顶间隙泄漏流试验测量和机理分析的难题, 该文提出一种基于全窗透明转轮室、等距弦长测量截面和旋转同步锁相的粒子图像测速(PIV)试验测量方法, 实现了混流泵叶顶间隙泄漏流的精细化试验测量。基于该方法, 搭建了水力机械综合性能试验台, 加工了一台比转速为484的混流泵, 系统测量了叶片头部到尾部6个测量截面上速度、涡量和涡结构分布。结果表明, 随着流量增加, 测量截面内相对速度逐渐增大, 额定流量下其方向与叶片型线基本一致, 验证了叶片水力设计的合理性。轴向速度随着流量增大而不断增大, 但受泄漏流影响分布逐渐不均匀, 叶片吸力面附近形成低速区, 并随泄漏涡向下游迁移逐渐偏离叶片。此外, 泄漏涡由泄漏流与主流剪切作用产生, 其面积和涡量从叶片头部到尾部均呈先增后减趋势, 面积峰值位置随流量增大依次迁移至30%、60%和80%弦长处, 涡量峰值则集中于40%~60%弦长区间。该研究揭示了叶顶间隙泄漏流的空间分布特征及其随流量的变化规律, 为混流泵优化设计与稳定运行提供了基础支撑。

Objective: This study addresses the challenges in experimental measurement and mechanism analysis of tip leakage flow (TLF) in rotating impellers by developing an advanced particle image velocimetry (PIV) methodology. The proposed methodology integrates a fully transparent shroud, equidistant chord-length measurement sections, and phase-locked rotational synchronization to achieve high-resolution visualization and quantification of TLF dynamics in a mixed flow pump. Methods: A comprehensive experimental platform was established at the State Key Laboratory of Hydroscience and Engineering, Tsinghua University; this included a closed-loop hydraulic test rig and a high-precision PIV system. The mixed flow pump used for testing featured a specific speed of 484, five-blade impeller, six-blade guide vane, and diameters of 150 mm at the inlet and 180 mm at the outlet. The PIV system features a 30-W laser with a 532-nm wavelength, a FASTCAM NOVA S12 high-speed camera, and SiO₂ tracer particles ranging in size from 10 to 50 μm. This setup achieved a spatial measurement resolution of 20 μm. Six equidistant chord-length sections (0, 0.2C, 0.4C, 0.6C, 0.8C, and 1.0C) along the blade chord direction were selected for analysis under three flow conditions: part-load (0.8Q_d), rated (1.0Q_d), and over-load (1.2Q_d), where Q_d = 34.5 kg/s. A phase-locked synchronization technique ensured repeatability for all measurements, maintaining a phase error of less than 1° and a temporal resolution of 0.115 ms. Post-processing of the datasets was conducted with SM-MICROVEC software, which utilized Gaussian filtering and AI-enhanced algorithms to calculate velocity and vorticity distributions. This approach enabled detailed measurement of the velocity fields, vorticity patterns, and vortex structures along the six sections. Results: The results show that relative velocity increased with higher flow rates, aligning with the blade profile direction at 1.0Q_d, validating the hydraulic design. Axial velocity rose with increasing flow rates but exhibited significant non-uniformity owing to the presence of low-velocity zones created by TLF near the suction surface. These zones migrated downstream, deviating from the blade's trailing edge. Absolute velocity reached its highest values at the mid-blade region but showed notable reductions near the tip, where interactions between tip leakage vortex (TLV) and wall shear forces dominated. TLV formed via shear interaction between TLF and mainstream flow. The area and vorticity intensity of the TLV exhibited a "rise-then-decline" trend along the blade chord, starting at the leading edge (0) and extending to the trailing edge (1.0C). TLV area peaks shifted downstream with increasing flow: 0.3C (0.8Q_d), 0.6C (1.0Q_d), and 0.8C (1.2Q_d). Vorticity peaks concentrated at 0.4C-0.6C across all conditions. At 1.0Q_d, the TLV occupies about 50% of the flow path at 0.6C and extends toward the hub at 1.0C. As the flow velocity increases, the separation vortex near the shroud inlet shrinks in the direction of increasing radius. The TLV interacts with these structures at 0.8Q_d but remains isolated at 1.0Q_d and 1.2Q_d. Ω standard analysis (Ω=0.52) shows structures associated with TLVs that vary in position with flow rate and string length, extending from the shroud to the midspan of the hub at 1.0Q_d. Conclusions: The proposed PIV methodology effectively resolves TLF characteristics in rotating machinery. The integration of a transparent shroud and phase-locked PIV system enables detailed quantification of TLF spatiotemporal evolution. TLF significantly disrupts axial velocity uniformity, forming downstream-propagating low-speed zones. TLV dynamics correlate strongly with flow rate, with peak intensity and spatial influence varying along the blade chord. These insights provide critical data for optimizing mixed-flow pump designs, aiming to mitigate energy losses and hydrodynamic instabilities induced by TLF.