Optimization of differential infrared thermography for unsteady boundary layer transition measurement

Journal article (2019)

Authors

C. Christian Wolf Deutsches Zentrum für Luft- und Raumfahrt (DLR)

C. Mertens Aerodynamics - Aerospace Engineering

Anthony Gardner Deutsches Zentrum für Luft- und Raumfahrt (DLR)

Christoph Dollinger University of Bremen

Andreas Fischer University of Bremen

Research Group

Aerodynamics (Aerospace Engineering) (TU Delft)

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Published Date

2019-1

Language

English

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Faculty

Aerospace Engineering

Department

Flow Physics and Technology

Research Group

Aerodynamics

Abstract

Abstract: Differential infrared thermography (DIT) is a method of analyzing infrared images to measure the unsteady motion of the laminar–turbulent transition of a boundary layer. It uses the subtraction of two infrared images taken with a short-time delay. DIT is a new technique which already demonstrated its validity in applications related to the unsteady aerodynamics of helicopter rotors in forward flight. The current study investigates a pitch-oscillating airfoil and proposes several optimizations of the original concept. These include the extension of DIT to steady test cases, a temperature compensation for long-term measurements, and a discussion of the proper infrared image separation distance. The current results also provide a deeper insight into the working principles of the technique. The results compare well to reference data acquired by unsteady pressure transducers, but at least for the current setup DIT results in an additional measurement-related lag for relevant pitching frequencies. Graphical abstract: [Figure not available: see fulltext.]

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