HEAT TRANSFER COEFFICIENT AND ADIABATIC EFFECTIVENESS MEASUREMENTS ON A NOZZLE GUIDE VANE WITH A SINGLE ROW OF CYLINDRICAL HOLES

Film cooling injection significantly affects the thermal behaviour of turbine vane surfaces. In addition to the beneficial effect of the film shielding the vane from the hot gas flow, alteration of the thermal boundary layer should also be taken into account. The aim of the present work is to detail the film cooling performance in terms of adiabatic effectiveness and external heat transfer coefficient on a 2D nozzle guide vane. A single row of cylindrical holes was tested on both pressure and suction side of a literature vane, the VKI LS89, in a linear cascade. The employed measurement technique is a transient thermal method based on IR thermography, which was thoroughly described and validated in a previous work. The influence of inlet free stream turbulence and blowing ratio was evaluated, and two different injection angles were considered for both pressure and suction side. Spatially resolved distributions of adiabatic effectiveness and heat transfer coefficient on the vane surface allow to precisely quantify the above mentioned aspects and highlight qualitative differences between pressure and suction side behaviour. Details regarding the generated non-uniformities in the measured parameters could be also provided, to emphasize how average quantities are not always sufficient to characterize such complex phenomena. The impact of different reference conditions to scale HTC results was also investigated. Such effect was found not negligible on the overall performance of the film cooling system, especially on the suction side where transition plays a critial role. Ultimately, the collected results constitutes a wide and detailed experimental database for numerical modeling validation in a well-studied environment as the LS89 configuration.