Numerical studies of rounded-dimple effect on unsteady film cooling and heat transfer performances for cutback surface at turbine vane trailing edge

Pressure-side cutback configurations have been widely applied to provide efficient thermal protection for the trailing edge of a turbine vane. Applying the rough cutback surface (e.g., dimpled surface) can enhance the convective heat transfer. However, the film cooling effectiveness may decay due to more sophisticated coolant/mainstream interactions. In this study, rounding the edges of dimples was proposed to resolve the conflict between high film cooling effectiveness and high heat transfer coefficient. The unsteadiness in momentum mixing and energy transport at dimpled surfaces and its influence on cooling performance were revealed by the transient scale adaptive simulation (SAS) method. The typical dimple structures decrease the film cooling effectiveness because the unsteady flow separation at the dimple edges amplifies turbulent fluctuations, which strengthen the energy transport between the mainstream and the coolant. In contrast, the rounded dimples can weaken the excessive turbulent mixing and maintain high film cooling effectiveness. In terms of heat transfer performance, dimples can increase the heat transfer coefficient by enhancing the turbulent heat diffusion in the near-wall region. While the diminished flow separation of the rounded dimples can reduce the low-speed reflux regions and expand the areas with high temperature convection, further improving heat transfer. The heat transfer coefficient of the rounded-dimpled surface reaches 1.35 times that of the smooth surface under the coolant-to-mainstream blowing ratio of 0.65. The results under different blowing ratios demonstrate that the rounded-dimpled cutback surface can achieve the twofold goal of high film cooling effectiveness and large heat transfer coefficient augmentation.