Experiments in Fluids

, 60:19 | Cite as

Optimization of differential infrared thermography for unsteady boundary layer transition measurement

  • C. Christian WolfEmail author
  • Christoph Mertens
  • Anthony D. Gardner
  • Christoph Dollinger
  • Andreas Fischer
Research Article


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



One-meter wind-tunnel Göttingen


Differential infrared thermography


German Aerospace Center


Infrared thermography

List of symbols


Chord length, \(c={0.3\,\hbox {m}}\)


Skin-friction coefficient


Lift coefficient


Pressure coefficient


Fluid specific heat capacity, J/m\(^3\)/K


Pitching frequency, Hz


Reduced frequency, \(k = \pi f c/V_\infty\)


Freestream Mach number


Convective heat flux, W/m\(^3\)


Reynolds number


Time, s


Airfoil surface temperature, K or counts


Freestream temperature, K


Freestream velocity, m/s


Coordinate along the airfoil’s chord line, m


Transition position, m

Greek symbols


Geometric angle of attack, deg

\({\overline{\alpha }}\)

Mean value of the angle of attack, deg

\({\widehat{\alpha }}\)

Amplitude of the angle of attack, deg


Difference between two values

\(\varDelta T_\mathrm{p}\)

DIT peak height, counts


Density, kg/m\(^3\)

\(\sigma C_\mathrm{p}\)

Standard deviation of the pressure coefficient



The studies were conducted in the framework of the DLR project “FAST-Rescue”.


  1. Coder JG (2017) OVERFLOW rotor simulations using advanced turbulence and transition modeling. In: 55th AIAA aerospace sciences meeting, AIAA SciTech Forum, Grapevine, TX, USA, Jan 9–13, 2017.
  2. Drela M (1990) Newton solution of coupled viscous/inviscid multielement airfoil flows. In: AIAA 21st fluid dynamics, plasma dynamics and lasers conference, Seattle, WA, USA, June 18–20, 1990.
  3. Gardner AD, Richter K (2015) Boundary layer transition determination for periodic and static flows using phase-averaged pressure data. Exp Fluids 56(6):119. CrossRefGoogle Scholar
  4. Gardner AD, Richter K (2016) New results in numerical and experimental fluid mechanics X, Springer International Publishing, chap transition determination on a periodic pitching airfoil using phase averaging of pressure data, pp 291–301.
  5. Gardner AD, Wolf CC, Raffel M (2016) A new method of dynamic and static stall detection using infrared thermography. Exp Fluids 57(9):149. CrossRefGoogle Scholar
  6. Gardner AD, Eder C, Wolf CC, Raffel M (2017) Analysis of differential infrared thermography for boundary layer transition detection. Exp Fluids 58(9):122. CrossRefGoogle Scholar
  7. Goerttler A, Gardner AD, Richter K (2017) New results in numerical and experimental fluid mechanics XI, Springer International Publishing, chap unsteady boundary layer transition detection by automated analysis of hot film data, pp 387–396.
  8. Lorber PF, Carta FO (1992) Unsteady transition measurements on a pitching three-dimensional wing. In: Fifth symposium on numerical and physical aspects of aerodynamic flows, Long Beach, CA, USA, Jan 13–15, 1992Google Scholar
  9. Merz CB, Wolf CC, Richter K, Kaufmann K, Mielke A, Raffel M (2017) Spanwise differences in static and dynamic stall on a pitching rotor blade tip model. J Am Helicopter Soc 62(1):1–11. CrossRefGoogle Scholar
  10. Overmeyer A, Heineck JT, Wolf CC (2018) Unsteady boundary layer transition measurements on a rotor in forward flight. In: 74th annual forum of the American Helicopter Society, Phoenix, AZ, USA, May 14–17, 2018Google Scholar
  11. Overmeyer AD, Martin PB (2017a) The effect of laminar flow on rotor hover performance. In: 73rd annual forum of the American Helicopter Society, Fort Worth, TX, USA, May 9–11, 2017Google Scholar
  12. Overmeyer AD, Martin PB (2017b) Measured boundary layer transition and rotor hover performance at model scale. In: 55th AIAA aerospace sciences meeting, AIAA SciTech Forum, Grapevine, TX, USA, Jan 9–13, 2017.
  13. Raffel M, Merz CB (2014) Differential infrared thermography for unsteady boundary-layer transition measurements. AIAA J 52(9):2090–2093. CrossRefGoogle Scholar
  14. Raffel M, de Gregorio F, de Groot K, Schneider O, Sheng W, Gibertini G, Seraudie A (2011) On the generation of a helicopter aerodynamic database. Aeronaut J 115(1164):103–112. CrossRefGoogle Scholar
  15. Raffel M, Merz CB, Schwermer T, Richter K (2015) Differential infrared thermography for boundary layer transition detection on pitching rotor blade models. Exp Fluids 56(2):30. CrossRefGoogle Scholar
  16. Raffel M, Gardner AD, Schwermer T, Merz CB, Weiss A, Braukmann J, Wolf CC (2017) Rotating blade stall maps measured by differential infrared thermography. AIAA J 55(5):1753–1756. CrossRefGoogle Scholar
  17. Richter K, Schülein E (2014) Boundary-layer transition measurements on hovering helicopter rotors by infrared thermography. Exp Fluids 55(7):1755. CrossRefGoogle Scholar
  18. Richter K, Schlein E, Ewers B, Raddatz J, Klein A (2016a) Boundary layer transition characteristics of a full-scale helicopter rotor in hover. In: 72nd annual forum of the American Helicopter Society, West Palm Beach, FL, USA, May 17–19, 2016Google Scholar
  19. Richter K, Wolf CC, Gardner AD, Merz CB (2016b) Detection of unsteady boundary layer transition using three experimental methods. In: 54th AIAA aerospace sciences meeting, San Diego, CA, USA, Jan 4–8, 2016Google Scholar
  20. Schreck SJ, Faller WE, Helin HE (1998) Pitch rate and reynolds number effects on unsteady boundary-layer transition and separation. J Aircr 35(1):46–52. CrossRefGoogle Scholar
  21. Schülein E (2008) Experimental investigation of laminar flow control on a supersonic swept wing by suction. In: 4th flow control conference, fluid dynamics and co-located conferences, Seattle, WA, USA, June 23–26, 2008.
  22. Schülein E (2014) Optical method for skin-friction measurements on fast-rotating blades. Exp Fluids 55(2):1672. CrossRefGoogle Scholar
  23. Tanner W, Yaggy P (1966) Experimental boundary layer study on hovering rotors. J Am Helicopter Soc 11(3):22–37. CrossRefGoogle Scholar
  24. Truckenbrodt EA (2008) Fluidmechanik Band 2: Elementare Strömungsvorgänge dichteveränderlicher Fluide sowie Potential- und Grenzschichtströmungen. Springer, BerlinzbMATHGoogle Scholar
  25. Vieira BA, Kinzel MP, Maughmer M (2017) CFD hover predictions including boundary-layer transition. In: 55th AIAA aerospace sciences meeting, AIAA SciTech Forum, Grapevine, TX, USA, Jan 9–13, 2017.
  26. Wadcock AJ, Yamauchi GK, Driver DM (1999) Skin friction measurements on a hovering full-scale tilt rotor. J Am Helicopter Soc 44(4):312–319. CrossRefGoogle Scholar
  27. Weiss A, Gardner AD, Klein C, Raffel M (2017) Boundary-layer transition measurements on mach-scaled helicopter rotor blades in climb. CEAS Aeronaut J 8(4):613–623. CrossRefGoogle Scholar

Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.German Aerospace Center (DLR)Institute of Aerodynamics and Flow TechnologyGöttingenGermany
  2. 2.Bremen Institute for Metrology, Automation and Quality Science (BIMAQ)University of BremenBremenGermany

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