Thermal Performance of Cooled Tips in a High-Pressure Turbine Cascade

The thermal performance of the three turbine tips was investigated. The results are presented in terms of heat-transfer coefficient (h), cooling effectiveness (eta) net heat-flux reduction (NHFR), and heat load. The calculations were performed using a cooled flat tip, a cooled cavity tip, and a cooled suction-side squealer tip in a cascade at a tip gap of 1.6%C. The results were validated using experimental data where possible. For an uncooled flat tip, the fluid dynamics are dominated by flow separation at the pressure-side edge. A significant benefit of ejecting coolant inside this separation bubble is shown. At the coolant mass-flow ratio M-c = 0.52%, both the cooled flat tip and the cooled cavity tip are well-protected by the coolant. For the cooled suction-side squealer tip, the coolant lifts off from the tip floor and leads to not only low cooling effectiveness, but also to high heat-transfer coefficients. The effects of the coolant mass-flow ratio on the thermal performance of the tip were presented. The effects of end-wall motion on the thermal performance of the blade tip are found to be small in the current study.