Quantitative heat transfer measurements in hypersonic wind tunnels by means of infrared thermography

A description of infrared (IR) thermography, as it is employed in a hypersonic blowdown wind tunnel for the acquisition of high quality two-dimensional heat transfer data over aerodynamic surfaces, is given. It is shown that the availability of an IR scanning radiometer and a standard digital image processing (DIP) system in the laboratory provides the means for highly efficient (in terms of time and cost) heat transfer measurement, with accuracy levels comparable to those achieved by classical discrete point gauges, such as thin-film surface resistance thermometers and thermocouples. The advantages of IR thermal mapping over the classical techniques, not only in measuring heat transfer distributions over complex three-dimensional configurations and in locating and quantifying highly localized hot spots, but also in interpreting puzzling results observed on simple configurations, are illustrated using a series of examples. A discussion of the limitations of the technique indicates that most of such limitations are common to classical `zero-dimensional´ instrumentation as well