The measurement of the surface heating is very important particularly for estimating the thermal load at large Mach numbers. However, heat transfer is also frequently estimated at small Mach numbers because it is possible to determine the laminar-to-turbulent transition location due to the different heat transfer present in both flow states. Today, digital infrared cameras are usually applied because they are easy to handle and instantaneous temperature measurements at thousand of points are possible with a sampling rate in the kHz range. Depending on the sensor technology, these cameras are working in different wavelength regimes, namely: the short wavelength regime between 0.4 and 2-3 micrometer, the intermediate between 2-3 to 5 micrometer and the long range between 8 and 12 micrometer. In fluid mechanics the range between 2 and 5 micrometer is usually recorded as high resolution indium antimonite (InSb) or mercury cadmium telluride sensors are available. These sensors have excellent signal to noise ratio and are available with 14 bit dynamic range.
The IR measurement technique still holds a lot potential for improvements. The Institute of Fluid Mechanics and Aerodynamics works on enhancements in the following fields:
- Data acquisition in various temperature ranges
- Calibration and noise reduction for accurate heat tranfer measurements
- Quantitative data evaluation and analysis
- Simultaneous application with other measurement techniques like PSP, deformation measurement technique, and PIV