Film cooling is widely applied as an effective way to maintain the turbine blade temperature at an acceptable level. The present paper investigates the overall cooling effectiveness and flow structure by performing conjugate heat transfer simulations for the flat-plate baseline cylindrical and three cratered film-cooling holes. The flow and heat transfer in the fluid domain is obtained using the Shear Stress Transport turbulence model, and the solid conductivity is considered by solving the Laplace equation. Four blowing ratios ranging from 0.5 to 2.0 are studied. The numerical results show that the concentric elliptic cratered hole yields a slightly higher overall cooling effectiveness than the baseline cylindrical hole, but the two contoured cratered holes exhibit great improvements due to the generation of the anti-kidney-shaped vortex pair. The area-averaged overall cooling effectiveness has improved by 5.58–65.30% for the contoured cratered hole. The variation of Biot number results in small change in the area-averaged overall cooling effectiveness. However, the area-averaged overall cooling effectiveness uniformity coefficient depends on the Biot number.

The cratered film-cooling hole is regarded as one of the potential applications with high cooling performance and low cost. This study focuses on the influence of the protrusion shape for the contoured crater embedded in the cylindrical hole. Four protrusion shapes, i.e., arc, rectangle, trapezoid, and triangle, are considered. The cooling effectiveness, flow structure, and aerodynamic loss for the cratered holes at blowing ratios of 0.5-2.5 are obtained using the numerical method with the Shear Stress turbulence model. The numerical results indicate that the arc and triangle protrusion models provide better lateral coolant coverage and higher area-averaged cooling effectiveness at higher blowing ratios, attributed to the ascendant anti-kidney-shaped vortex pair. The rectangle protrusion model provides the lowest area-averaged cooling effectiveness because the kidney-shaped vortex pair dominates the downstream flow field. For the aerodynamic loss, the largest total pressure loss coefficient occurs for the rectangle protrusion model and nearly equivalent values for the other three protrusion models. The contoured cratered holes with arc and triangle protrusions are generally recommended.