Thermal Performance of Different Cooled Tips in A High-Pressure Turbine Cascade

Abstract

The thermal performance of the three turbine tips was investigated. The results are presented in terms of heattransfer coefficient (h), cooling effectiveness (), 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.

Thermal Performance of Transonic Cooled Tips in a Turbine Cascade

“…Computational fluid dynamics (CFD) tools were found to be able to produce good predictions of the thermal performance of the tip leakage flow in a number of studies, both at subsonic conditions (e.g., Zhou et al [9]) and at transonic conditions (e.g., Zhang et al [18]). In the current study, the commercial code ANSYS FLUENT is used to solve steady Reynolds-averaged Navier-Stokes (RANS) equations.…”

“…The mesh of the flat tip used later in this paper has a tip Y of 3.7. The grid dependency study carried out at low speed (Zhou et al [9]) showed that the average heat transfer coefficient on the blade tip changes less than 4% when varying the tip Y from 2.8 to 7. This suggests that the prediction of the tip heat transfer coefficient is more sensitive to tip Y at highspeed conditions.…”

“…Grid dependency studies were carried out at both transonic (Table 1) and low-speed conditions (Zhou et al [9]). The mesh dependency study showed that there was little change in the thermal performance when decreasing the growth factor from less than 1.3 to less than 1.2 for both high-speed and low-speed cases.…”

“…Similar results were obtained by Kwak and Han [13,14] in a subsonic turbine cascade. The thermal performance of cooled tips was also studied by Hohlfeld et al [15] and Zhou et al [9] in low-speed turbine cascades. However, few publications provide detailed investigations of the thermal performance of transonic cooled tips.…”

“…To reduce the heat load of the tip, the thermal performance of different parts, such as the squealer surfaces of the cavity tip, should be considered. Zhou et al [9] showed that the heat load of an uncooled cavity tip is higher than that of an uncooled flat tip due to the increased surface area in a low-speed cascade.…”