Quantitative Infrared Thermography in Short-duration Facilities

Department High Speed Configurations

Background

Aerodynamic heating during re-entry of space vehicles at hypersonic speeds is one of the key problems of space transportation as the knowledge of the heating rates is very important for the dimensioning of the thermal protection systems. For quantitative heat transfer measurements in short-duration facilities a high-speed infrared camera is applied by the DLR Institute of Aerodynamics and Flow Technology..

Measurement Technique

Infrarot Schülein
Some examples of heat-flux measurements on spherically-blunted spiked bodies obtained in the Ludwieg Tube Facility at DLR Göttingen and described in detail in Schülein (2010). The measured heat flux density is presented as Stanton-number distribution.
Within the scope of the thick-wall transient measurement technique a solid or thick walled model made of material of low thermal conductivity is used. The history of the surface temperature is recorded during the wind tunnel run and used to determine the heat transfer rate by consideration of the semi-infinite wall thickness. The IR-camera is based on a highly sensitive 640x512 FPA-sensor, which requires only an exposure time of 10-100 µs for temperature measurements. Access to the test section is given by a special IR-window (Germanium), optimized by a both side anti-reflex coating for use in the range of wave lengths required.

The evaluation of the measured temperature pictures is analyzed by the self developed software tool HeatFIT that allows a fast calculation and visualization of heat flux distributions directly after the test run. The automatic marker-based 3D-reconstruction of the thermal images and the mapping of the data values onto the 3D grid of the model surface, implemented in this tool, enables some precise heat-flux calculations also at vibrating or moving (e.g. rotating) test objects. The analysis of the data on the node points of these surface grids facilitates the comparison with results of complementary CFD-calculations.

Typical results of heat-flux measurements on a body of revolution, evaluated by HeatFIT and visualized via TECPLOT, are presented on the picture right.

This technique is not limited only to short-duration wind tunnels and can be used in continuous working facilities for qualitative heat-flux measurements (transition-detection, etc.).

Publications on this topic

  • Schülein E., “Skin Friction and Heat Flux Measurements in Shock Boundary Layer Interaction Flows”, /AIAA-Journal/, Vol.44, No.8, Aug. 2006, pp.1732-1741
  • Kovar A. and Schülein E. (2008) “Visualisation and Prediction of Heat Flux Measured on the Example of Side Jet Control,” 13th International Symposium on Flow Visualisation, 01.-04.07.2008, Nizza, Frankreich
  • Schülein E. (2008) “Experimental Investigation of Laminar Flow Control on a Supersonic Swept Wing by Suction”, AIAA Paper 2008-4208, 4th AIAA Flow Control Conference, Seattle, Washington (USA), 23. – 26.06.2008, 14p
  • Schülein E. (2010) “Shock-wave control by permeable wake generators”, AIAA 2010-4977, 5th AIAA Flow Control Conference, Chicago, Illinois (USA), 28. Jun. - 01. Jul.2010


 


Contact
Dr.rer.nat. Erich Schülein
German Aerospace Center

Institute of Aerodynamics and Flow Technology
, High Speed Configurations
Tel: +49 551 709-2803

Fax: +49 551 709-2811

E-Mail: Erich.Schuelein@dlr.de
URL for this article
http://www.dlr.de/as/en/desktopdefault.aspx/tabid-333/378_read-2937/
Texte zu diesem Artikel
Department High Speed Configurations (AS-HGK) (http://www.dlr.de/as/en/desktopdefault.aspx/tabid-333/378_read-559/usetemplate-print/)