Precise infrared thermometry with considering background radiation for gas turbine air cooling application

Abstract

The turbine inlet temperature keeps increasing as high-efficient gas turbines have been developed for the last decades. The increase of turbine inlet temperature makes the turbine blades being exposed in thermally severe conditions, leading to thermal damage. The thermal management with advanced cooling techniques is thus necessary to protect turbine blades from thermal deformations. For properly evaluating the air-cooling effects on turbine blades, the more accurate surface temperature measurement must be preceded. Infrared thermometry has often been employed for high-temperature turbine blades due to its convenience. However, background radiation must be carefully considered if the surrounding environment is at a higher temperature than the surface to be measured, as in the case of a gas turbine blade. In addition, the spectral emittance of an object should also be known a priori. In this study, we propose an accurate measurement scheme of infrared thermometry by properly considering the background radiation from the high-temperature environment as well as the spectral emittance of an object. The accuracy of infrared thermometry was examined for two exemplary surfaces with low and high emittance in a high-temperature wind tunnel. The proposed measurement scheme was found to be in good agreement with the thermocouple measurements within 5% for both surfaces.