Internal Temperature Measurements Using Fiber Optics in Engine-Scale Gas Turbine Blade

Further improvements in gas turbine performance can be achieved by increasing turbine entry temperatures. As current entry temperatures significantly exceed the melting temperatures of turbine blade materials, advanced cooling configurations, manufacturing techniques, and thermal barrier coatings are required to protect the blade. While surface temperatures can be measured to evaluate system effectiveness, limited techniques exist to capture internal metal temperatures due to the small sizes and complex geometries of blades. However, internal temperatures are critical to managing thermal gradients and ensuring blade life. This paper demonstrates the use of fiber Bragg gratings (FBGs) to measure internal temperature fields at high spatial resolution in difficult-to-access locations. Temperature changes are monitored through changes in the reflected wavelength of the gratings, which act as optical filters inscribed within a silica waveguide core. A single 0.15-mm-diameter fiber can contain many gratings capable of withstanding harsh turbine conditions. In this investigation, a turbine blade instrumented with 20 FBGs is tested in the Oxford Thermofluids Institute High Temperature Linear Cascade. The measurements are compared to thermocouple temperatures and surface temperatures from infrared thermography. To the authors’ knowledge, this is the first report of embedding FBGs in a cooled, engine-scale turbine blade to measure metal effectiveness.