Platform Film Cooling Investigation on an HP Nozzle Vane Cascade With Discrete Shaped Holes and Slot Film Cooling

The present paper reports on an experimental investigation carried out at Bergamo University in cooperation with Ansaldo Energia with the aim of assessing the aerodynamic and heat transfer performance of a high-pressure nozzle vane cascade with and without platform cooling. The results of the original cooling scheme based on cylindrical holes have been presented in a previous paper (Barigozzi et al. 2018. Aerodynamic and Heat Transfer Experimental Investigation of a Film Cooled HP Nozzle Vane Platform, GT2018-75038) and are considered as a reference. The present paper is a step forward in this investigation, presenting on the results obtained from testing two different cooling schemes: the first one based on shaped holes distributed over the passage and the second one featuring a slot located upstream of the leading edge plane simulating the combustor to stator interface gap. Tests were run on a 6-vane cascade reproducing the first nozzle vane profile with a 1:1 scaling. The wind tunnel was operated at an isentropic cascade exit Mach number of 0.7 and a significant inlet turbulence intensity level of about 9%.

The cooling schemes implemented in the cascade model were first aerodynamically tested to quantify their impact on secondary flows and related losses for variable injection conditions. Heat transfer performance was then assessed through the measurement of the adiabatic film cooling effectiveness and of the convective heat transfer coefficient. The first was measured either with binary Pressure Sensitive Paints (shaped holes) or with the TLC technique (slot), the second with the transient TLC technique. From this data, the Net Heat Flux Reduction (NHFR) parameter was computed to critically assess the cooling schemes. The collected results allowed to fully characterize the tested platform cooling schemes under variable injection conditions. In particular, when compared with the reference cylindrical scheme, shaped holes outperform for all tested injection rates, while the slot alone is able to thermally protect only the middle of the passage. Discrete holes would be required to cool the platform region along the whole pressure side and the suction side leading edge region.