High speed infrared thermography to investigate heat transfer of transonic turbine rotor blades

The role of infrared (IR) thermography has become increasingly predominant in aerothermal testing of gas turbine components in non-rotating engine representative experiments. However, efforts are ongoing to achieve accurate measurements in rotating experiments with target speeds in excess of ∼200 m/s and surfaces temperatures below 500 K. A novel measurement system employing IR thermography was developed for the Oxford Turbine Research Facility (OTRF), a UK national engine-representative high-pressure turbine test facility operating with rotational speed of 8,500 rpm and transonic flow. The infrared measurements focussed on estimating the temperatures of uncooled blade squealer tips with a target velocity of 263.5 ms⁻¹. The aerothermal design of this region is key for engine efficiency and blade life. Correction of all sources of errors are applied to the IR raw thermal data, obtaining results as two-dimensional maps of target temperature following procedures developed by Sisti et al. [1]. A range of camera integration times varying from 20 to 1 µs was tested to investigate the effect on image quality and measurement accuracy, allowing deeper understanding on the effects of noise, detector undersaturation and image blur. Results obtained with an integration time of 20, 10, 5, 2, and 1 µs are firstly compared as blackbody equivalent temperatures. Subsequently, data acquired with camera integration time of 10, 5, and 1 µs is processed to scalable heat transfer quantities (i.e. adiabatic wall temperature and Nusselt number) for the first time in literature for a turbine blade in rotating, transonic test facility. Finally, a detailed post-test uncertainty analysis is presented. This study demonstrates the capability of IR to capture temperature and heat transfer phenomena at high speed in gas turbine research and highlights the impact of the camera integration time on image quality and temperature measurement accuracy.