Effects of Cutback Tip Trailing Edge Squealer on Turbine Blade Tip Thermal Behaviour Under High-Speed Relative Casing Motion

Abstract In extreme operating conditions, over-tip-leakage (OTL) flow introduces high thermal load to high-pressure turbine blade tips, which can cause severe material damage and consequently affect the performance and reliability of the entire device. Tip trailing edge region is usually the initial and most susceptible area to thermal damage. The cutback tip trailing edge squealer design is a practical engineering option to facilitate the cooling of the trailing edge. This study examined the tip aerothermal behaviour of full cavity, pressure- and suction-side cutback tip squealers. For the first time, the thermal performance of cutback tip squealer designs under high-speed relative casing motion was experimentally revealed. By Computational Fluid Dynamics (CFD) method, the results indicate that the suction-side cutback tip squealer significantly enhances the heat transfer inside the cavity due to the prolongated stay of the cavity vortex. This effect is more evident when more of the suction-side trailing edge rim is removed. The experimental results suggest that the averaged tip heat transfer coefficient of the 75% axial chord (Cx) suction-side cutback squealer is 18% higher than that of full squealer tip in the cavity floor region, and 8.44% higher in the whole blade tip region. On the other hand, the pressure-side cutback squealer exhibits close overall tip aerothermal performance to that of the full cavity tip, making it a recommended design in engineering practice. Furthermore, as the tip clearance size increases, the effects of cutback tip squealers become more insignificant.