Viability of Fiber Optic Temperature Sensors Embedded Within Engine-Scale Turbine Blades

Abstract

Abstract Small variations in temperature across a gas turbine blade can have significant impacts on engine fuel efficiency, power output, and blade life. Therefore, an improved understanding of the temperature distribution on the surface of and within a gas turbine blade supports optimization of cooling systems and blade structures. While established methods exist for external blade surfaces, limited methods exist to capture the temperature distribution within the internal structure. Due to the small sizes of blades and the complex cooling configurations they contain, optical access is limited, and sufficient spatial resolution is difficult to obtain. This paper explores the viability of embedding fiber optic temperature sensors within engine-scale turbine blades. Given their minimally invasive nature, potential for multiplexing, and ability to operate in harsh conditions, fiber optic sensors present an opportunity to capture detailed temperature data for research and development or in-situ health monitoring. Specifically, fiber Bragg gratings (FBGs), or narrow band filters which reflect certain wavelengths of light, can be used to sense physical parameters such as strain and temperature. A single optical fiber with a diameter of less than 0.2 mm can contain many FBGs along its length, allowing for measurements with high spatial resolution. Additionally, the high temperature capabilities of FBGs create sensors well-suited for the harsh conditions present in turbine blades. This paper identifies and explores obstacles to the embedding of FBG sensors within engine-scale blades. Three primary challenges include routing through complex configurations, achieving thermal contact between the sensor and blade, and decoupling strain and temperature for embedded measurements. This study evaluates how routing and embedding fiber optic sensors within a blade impact the measurements acquired. Following this study, instrumentation of a cooled, engine-scale blade with fiber optic temperature sensors will be undertaken in a linear cascade at the Oxford Thermofluids Institute.