Experimental and numerical investigations on film cooling performance of converging slot holes in plate and turbine conditions

•Converging slot holes were investigated by using PSP experiments and numerical simulations.•The cooling performance of a converging slot hole was strongly dependent on the width of the hole exit.•The case with Lw = 2.3d obtained the highest level of adiabatic effectiveness from spanwise and streamwise views.•Converging slot holes had better performance on film cooling effectiveness on the turbine endwall. Based on the heat-mass transfer analogy, the Pressure Sensitive Paint (PSP) technique was used to explore the film cooling characteristics of converging slot holes on the plate model and the actual turbine endwall model conditions. Meanwhile, the numerical calculation was also adopted to pursue the flow field details. The width of the converging slot hole exit is a key geometry affecting cooling performance. On the plate model condition, three widths of exit slot Lw (1.7d, 2.3d, 2.9d) were chosen to obtain the optimal exit width. The case with Lw = 2.3d obtained the highest level of adiabatic effectiveness from spanwise and streamwise views. This case operated as a two-dimensional slot and produced a more uniform cooling jet film relative to other cases. Nevertheless, the cooling performance decreased significantly as the converging slot hole width increased to Lw = 2.9d. Then the cooling performance of three patterns of film holes was further investigated in the turbine endwall. Laid-back fan-shaped holes and converging slot holes could improve the film cooling performance effectively compared to the cylindrical holes. Converging slot holes with Lw = 2.3d improved the uniformity of the cooling jet outflow through rows of upstream film holes, and also effectively avoided the phenomenon of coolant blowing away or high-temperature gas entering the film hole, resulting in high film cooling effectiveness performance. Compared to cylindrical holes, the area-averaged adiabatic effectiveness was increased by 216.5 % for the endwall with cylindrical holes with the momentum ratio I = 0.25. Overall, converging slot holes improved cooling performance among all studied film hole configurations.