Investigations into heat transfer and film cooling effect on a squealer-winglet blade tip

Numerical investigations of heat transfer and film cooling effect on the conventional squealer tip, no P.S. rim squealer tip and P.S. winglet squealer tip have been performed at three different cooling-hole arrangements (i.e. no film cooling, only tip holes, and both tip and pressure side holes) and two tip clearances. The flow structures, as well as the total pressure loss, in the cascades with three tip configurations (i.e. conventional squealer tip, no P.S. rim tip and P.S. winglet tip) were obtained and compared to analyze the effect of tip pressure-side geometries on the aerodynamic performance near the tip gap. With the existed experimental data for the conventional squealer tip, the numerical methods were carefully validated with respect to the turbulence model and mesh independency. The results indicate that the total pressure loss in the cascade with P.S. winglet tip is lower than that with conventional squealer tip by 5.0-6.7%, and the no P.S. rim tip shows a very close aerodynamic performance with the P.S. winglet tip configuration. In no film cooling case, the area-averaged heat transfer coefficient on the P.S. winglet tip surface is lower than that on the conventional squealer tip by 14.1-15.6%. In the tip holes only case, the area-averaged heat transfer coefficient on the P.S. winglet tip can be reduced by about 10% compared with the conventional squealer tip. As the tip clearance increases, the area-averaged heat transfer coefficient on no P.S. rim tip is getting lower than that on the P.S. winglet tip. With both tip and pressure side holes, the no P.S. rim and P.S. winglet tips still exhibit better film coolant coverage on the cavity floor than on conventional squealer tip, especially near the cavity pressure side. As the clearance gap increases, the film cooling effects on no P.S. rim and P.S. winglet tips become even better than that on the conventional squealer tip. As the clearance gap increases from 1% to 2.5% of blade span, the area-averaged film cooling effectiveness on the P.S. winglet and no P.S. rim tips are higher than the conventional squealer tip by 7.1-57.8%.