Thermography as a tool in wind tunnel testing

Abstract

The term “thermography” in general means the graphical visualization of temperature fields, or to give a more sophisticated definition: Thermography denotes the visualization and quantitative evaluation of the temperature on a body’s surface with the help of cameras (thermographic imaging). This is a widening of the method of thermometry, which in general denotes the measurement of temperatures using point sensors like thermo couples or resistance temperature detectors, for example. The most well known technique for thermographic imaging is the method of infrared thermography (IRT). In principle, IRT works by detecting the heat radiation emitted from a body surface with the help of suited sensors and calculating the corresponding temperature. In addition to IRT, several different techniques exist to visualize surface temperature variations. They are based on the temperature sensitivity of certain physical properties of molecules which are embedded in a binder matrix, i.e. they have to be applied to the surface as paint or as some kind of foil which can be bonded to the surface of interest. In the following sections the different methods for thermographic imaging will be described and their pros and cons with respect to their application in large wind tunnel testing will be highlighted. Special attention will be given to their usability as a tool for transition detection, i.e. the visualization of the laminar-turbulent transition of the boundary layer.