Experimental study on aerodynamic performance of turbine blade squealer tip with different trailing edge designs under high-speed relative casing motion

Over-tip leakage (OTL) flow leads to great aerodynamic performance reduction in high-pressure turbine, reasonable blade tip design can effectively control the loss caused by OTL flow. The relative casing motion is one of the key boundary conditions that can significantly influence OTL flow. In this study, aerodynamical tests were conducted for a high-pressure squealer tip with different trailing edge designs of full cavity squealer tip, pressure-side cutback and suction-side cutback at both stationary and rotating conditions. Loss distribution and blade near tip loading of different trailing edge structures at high-speed rotating condition are firstly reported and evaluated. The result indicates that pressure-side cutback design significantly increases the aerodynamic loss compared with full cavity tip, while suction-side cutback design has close overall loss to full cavity tip. This conclusion was consistent with numerical simulation based on Reynolds-averaged Navier–Stokes computational fluid dynamics (CFD) analysis, which reveals that pressure-side cutback design causes the cavity vortex leaks earlier compared with full cavity tip, a small vortex formed at cut region forms and results in higher total pressure loss. The effect of relative motion between blade tip and shroud reinforces this trend. The total pressure loss difference can reach 42 % compared with 8 % in stationary condition, which indicates that relative casing motion needs to be take into consideration when ranking different tip sealing designs.