Effects of non-axisymmetric endwall contouring on aerothermal performance of a gas turbine blade endwall with a purge flow

In view of the ever-increasing thermal load being placed on gas turbine blade endwalls, there is an urgent need to develop advanced endwall thermal management techniques. This paper proposes a non-axisymmetric endwall contouring method based on two parameterized control curves. The method is then applied to a blade endwall with an upstream purge flow. The effects of contoured endwalls with different maximum amplitudes on endwall aero-thermal performance are numerically investigated under three different mass flow ratios (MFR). The results indicate that, with endwall contouring, the strength of the horseshoe vortex and turbulent mixing of the mainstream and coolant can be both diminished, leading to a slightly lower aerodynamic loss. A contoured endwall significantly enhances the endwall film cooling effectiveness when MFR>1.0%, while having little impact when MFR = 0.5%, when compared to a flat endwall. More importantly, a contoured endwall significantly enlarges the film-cooling coverage near a blade leading edge, where the thermal load is extremely high. A contoured endwall with a maximum amplitude of 1.5% can substantially enhance the area-averaged film-cooling effectiveness by 41% when MFR = 1.0%. Furthermore, the contoured endwall also shows a considerable reduction in endwall heat transfer rates for all the MFRs investigated. It should be noted that the contouring amplitude for the lowest heat transfer rate also obtains the highest film cooling effectiveness when MFR>1.0%. The optimal contouring amplitude is found to be H/S = 1.5% and H/S = 1.0% for MFR = 1.0% and MFR = 1.5%, respectively. Overall, a contoured endwall with an appropriate contouring amplitude can significantly reduce the thermal load on endwalls, without any serious aerodynamic impact.