MEASUREMENTS OF THE COOLING PERFORMANCES OF A REAL COMBUSTOR LINER WITH AIR AND CO2 INJECTION THROUGH A SLOT AND AN ARRAY OF EFFUSION COOLING HOLES

Due to the higher cooling requirements of novel gas turbine combustor liners a comprehensive understanding of the phenomena concerning the interaction of hot gases with different coolant flows plays a major role in the definition of a well performing liner. The aim of this study is the investigation of the effects of density ratio between coolant and mainflow on a real engine cooling scheme of a combustor liner; measurement of heat transfer coefficient, adiabatic effectiveness and Net Heat Flux Reduction were performed by means of a steady-state Thermochromic Liquid Crystals (TLC) technique, considering the combined effects of slot, effusion cooling and dilution holes. Experiments were carried out imposing values of effusion blowing ratio and velocity ratio typical of modern engine working conditions (VReff - BReff = 3) and keeping constant slot flow parameters (BRsl~1.5); tests were carried out feeding the cooling system both with air and carbon dioxide (CO2), while hot air was used in the main channel. The experimental analysis was performed on a test article replicating a slot injection and an effusion array with a central large dilution hole. Test section consists of a rectangular cross-section duct and a flat perforated plate with 272 holes arranged in 29 staggered rows (d=1.65mm, Sx/d=7.6, Sy/d=6, L/d=5.5, =30°); a dilution hole (D =18.75mm) is located at the 14th row. Both effusion and dilution holes are fed by a channel replicating combustor annulus, that allows to control cold gas side cross-flow parameters, especially in term of Reynolds of both annulus and effusion holes. Upstream the first effusion row, a 6.0mm high slot ensure the protection of the very first region of the liner. Results point out the influence of density ratio on film cooling performance, suggesting that blowing ratio is the right parameter to scale the adiabatic effectiveness, while velocity ratio is suitable for heat transfer coefficient and NHFR.