Comparative SPIV Investigation of Leakage Flow in an Open Clearance at Different Spanwise Locations Under a Moving Endwall

Future commercial engines require higher bypass ratios and smaller cores, leading to open tip clearances exceeding 4% (s/H ≥ 4%) in rear stages. The resulting leakage flows show strong three-dimensional unsteady features that challenge numerical prediction, while experimental data inside open clearances with moving endwalls remain limited. In this study, a Stereo Particle Image Velocimetry (SPIV) system was applied to a high-speed moving-endwall cascade test rig. Measurements were conducted for a Controlled Diffusion Airfoil (CDA) cascade at Mach 0.3, an endwall speed of 900 r/min, and a relative clearance of 7.14%. Velocity fields were obtained on two spanwise planes, 2 mm (MP1) and 3.5 mm (MP2) from the endwall. Results show that the tip leakage vortex develops continuously along the span but differs between planes. In MP2, dominated by blade pressure difference, the leakage jet forms a broader high-velocity region and a more compact vortex, with higher blockage, shear gradient, and turbulent kinetic energy than in MP1. In MP1, endwall shear stretches the leakage flow pitchwise, reducing blockage and weakening mixing. This work demonstrates the feasibility of dual-camera SPIV measurements inside moving-endwall clearances and provides benchmark data for numerical validation.