Comparisons of Measured Blade Temperatures With Predictions Using Available Correlations

Abstract As turbine inlet temperatures have steadily increased over several decades, turbine blade designs have transformed to accommodate higher gas path temperatures through the addition of internal convective cooling, external film cooling, and protective thermal barrier coatings. First-order cooling effectiveness benefits of these different features can be predicted analytically through correlations presented throughout the literature and then validated experimentally. The challenge of recreating engine operating conditions in a laboratory environment means that experiments are typically conducted at scaled conditions, which necessitates the use of nondimensional parameters to relate the experimental results to the engine conditions. For this reason, experiments and corresponding correlations are often developed using scaling approaches with appropriate nondimensional parameters. This study compiles a first-order analysis using experimentally based correlations to predict cooling effectiveness for true-scale engine blades operated at scaled conditions in a one-stage turbine rig. To validate the correlations, turbine blade temperatures were measured using infrared imaging under rotating blade conditions for increasing levels of blade cooling flow and multiple cooling designs: internal convection only; blades with different thermal barrier coating thicknesses; and blades with internal convection and film cooling. For purposes of this study, a subset of shaped, compound-angle film holes was evaluated for overall cooling effectiveness and subsequently compared to results achieved from a one-dimensional analysis. Ultimately, this analysis showed the ability of available correlations to accurately predict cooling effectiveness changes within 3% of the experimentally measured values. Additionally, the validated heat transfer correlations were used to first infer the cooling benefit by further changing the designs and operating conditions and then investigate additional heat transfer effects of film cooling. Thermal barrier coatings and film cooling were observed to reduce heat flux substantially, but improved overall cooling effectiveness with distinct trends from each other when evaluating the heat load parameter.