Mechanisms of stripe-like heat transfer and shock-induced thermal loads on transonic turbine blade tips with varying clearances

This study investigates the influence of turbine blade tip clearance on thermal characteristics and flow structures through combined experimental and numerical methods. Three different tip clearance sizes (t = 0.50%, 0.83%, and 1.33% of the blade height) are analyzed in detail to reveal the underlying physical mechanisms of over-tip leakage (OTL) flow. The results demonstrate that enlarging the tip gap considerably increases the leakage mass flux, leading to a corresponding rise in the area-averaged heat transfer coefficient (HTC) on the tip by 8.2%. A distinctive stripe-like HTC pattern is observed in the midchord region of the tip, which is fundamentally attributed to the mixing of high-energy main leakage flow and low-energy near-wall fluid. As the clearance size increases, the scale of the leakage vortex expands, resulting in larger-scale heat transfer stripes. Furthermore, the study reveals that the heat transfer performance of transonic OTL flow is strongly influenced by complex shock wave structures. Flow separation and reattachment, induced by shock reflection and shock–boundary layer interaction, create alternating regions of high and low thermal load. In larger clearance cases, the emergence of normal shocks downstream further intensifies the heat load near the pressure side. The interaction between shock waves and the boundary layer, together with flow reattachment, increases heat load nonuniformity, and the high heat transfer region moves toward the midchord of the tip.