Hight Resolution Infrared Thermography for Airfoils Boundary Layer Inspection in Passive Mode

In thermo-fluid-dynamics, the important role played by the boundary layer phenomena is well known. In order to set up an experimental tool, able to measure fluid dynamic magnitudes in the boundary layer, many efforts have been made and some advanced measurements have been developed. Since the mid-sixties, infrared thermography has been applied as a measurement technique. Primarily, this technique was used in space missions where the protection of space vehicles in the reentry phase was of prime importance. Nowadays, thermography is one of the most advanced non-intrusive measurement techniques and presents many advantages such as no-needs for particular settings of system under analysis. Therefore, considering that boundary layer continues to be a fundamental aspect in fluid-dynamics studies, the present work wants to dwell on the possibility to enlarge the application of the infrared measurement technique, in particular for subsonic flows in passive mode. These conditions point out important problems of measurement for the low energy content and for the type of thermal exchange that can not be simplified as it is traditionally made in supersonic flows. Either the possibility to operate with modern infrared cameras or the improvements of new theoretical models in the data reduction process will be described in this paper and an application to an airfoil will be presented. The measurement technique used in this paper can be applied to any aerodynamic profile and can be easily used as a non intrusive technique to characterize the flow fields of blade cascades for gas tubrines and turbomachinery in general