Toleranced Designs of Cooled Turbine Blades Through Probabilistic Thermal Analysis of Manufacturing Variability

Abstract

Manufacturing variability is likely the primary cause of a large scatter in the life of gas turbine hot section components. This paper investigates manufacturing variability and its effect on first-stage turbine blades through the use of a parametric CAD model, automated CAD regeneration software, and a parametric finite element thermal model. The probabilistic approach used is substantiated due to differences that arise when input parameters vary at different levels, for example the engine-to-engine and blade-to-blade level. Schemes are proposed to improve robustness through tolerancing out input parameters in ranges of the distributions that make nonconformances more likely. A frame-work is presented for calculating the potential number of prevented non-conformances and the corresponding cost savings associated with various tolerancing schemes. Blade-to-blade cooling flow variability, especially as a result of film-hole diameter variability in critical locations, is identified as the most likely candidate for parameter tolerancing. More effective is a combined two-factor tolerancing scheme which additionally tolerances gas path temperature.