Methods to Extract Underlying Boundary Conditions from Transient Metal Effectiveness Measurements

Abstract

Metal effectiveness measurements (or overall cooling effectiveness measurements) are becoming increasingly used to understand complex coupled systems in gas turbine experimental research. Unlike traditional techniques in which individual boundary conditions are measured in isolation and superposed using a thermal model, metal effectiveness measurements give the final result of a complex coupled system. In correctly scaled experiments this allows aerothermal performance at near-engine conditions to be evaluated directly, and is thus powerful both as a research technique and for derisking engine development programs. The technique is particularly useful for evaluating the thermal performance of internally cooled turbine components, because of the complexity and degree of interaction of the underlying boundary conditions. An intrinsic limitation of metal effectiveness measurement data is that the individual boundary conditions (e.g., the internal and external heat transfer coefficients) cannot be directly obtained from the final measurement. Decoupling of these boundary conditions would allow deeper understanding of the systems that are the subject of experiments. The objective of this paper is to present methods to extract the individual underlying boundary conditions from data available in typical metal effectiveness experimental measurements, and to assess the uncertainty associated with decoupling techniques. Although we reference experimental data from advanced facilities for metal effectiveness research throughout, much of the analysis is performed using a low-order heat transfer model to allow the impact of experiment design and measurement errors to be clearly separated at each stage of the analysis.