Detailed showerhead cooling effectiveness measurements on the notched leading-edge surface: Effect of freestream turbulence and density ratio

The leading-edge cooling configuration with the notch design on the stagnation line proposed in the preliminary work may become a promising structure to reduce further the thermal load on the leading-edge of the high-pressure turbine vane. In the current study, steady-state pressure-sensitive paint technology is adopted as a measurement method to evaluate further the effect of freestream turbulence and the freestream-to-coolant density ratio on the spatially resolved film cooling effectiveness of this leading-edge configuration. Three freestream turbulence levels were obtained by changing the grid position. Regardless of whether the leading-edge configuration had a groove, the effect of freestream turbulence on film coverage was consistent when the coolant flow rate was low. An increase in the turbulence worsened the leading-edge film cooling effect. The enhancement of the turbulence within a certain range weakened the transmission of the film flow direction and drove the film to spread laterally, weakening the superimposition effect of the film in the flow direction. As the momentum ratio changed in a high freestream turbulence situation, the turning point for the second increase in film cooling effectiveness occurred even earlier. As the momentum ratio increased, the effect of turbulence on the leading-edge film cooling effectiveness gradually weakened. The density ratios of 1.4 and 2.5 were simulated by using varying gases. When the momentum ratio was constant, the showerhead cooling effectiveness increased with the density ratio, and the core region of film coverage for the downstream rows of holes was broader and longer. Furthermore, scaling analysis was performed for the experimental data. With a small coolant flow rate, the scaling with blowing ratio was capable of matching the showerhead cooling effectiveness; when scaling with momentum flux ratio can obtain a consistent change with only a difference in the numerical value.