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Boundary-layer transition measurements on hovering helicopter rotors by infrared thermography

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Abstract

High-speed infrared thermography was applied for boundary-layer transition measurements on the upper side of helicopter rotors. The transition detection is based on the analysis of a single instantaneous thermal image of the rotating blade and allows the determination of both the locations of the onset and of the end of the transition region. Measurements were performed on a Mach-scaled BO105 model rotor for different rotation frequencies. The transition characteristics are presented and compared to two-dimensional numerical simulations, and the measurement scatter is discussed. Additional transition measurements were performed on the main rotors of the DLR research helicopters Eurocopter BO105 and EC135. The transition behavior of the EC135 rotor blade is presented for different cases, and the effect of the contamination of the rotor blade leading edge on the laminar flow is discussed.

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Abbreviations

\(\alpha \) :

Angle of attack (°)

\(\rho _\infty \) :

Free stream density (kg/m\(^3\))

\(c\) :

Chord (m)

\(c_{\text {f}}\) :

Skin friction coefficient

c p :

Specific heat capacity (J/kg K)

c p :

Pressure coefficient

\(d\) :

Diameter (m)

\(f\) :

Rotation frequency (Hz)

\(h\) :

Heat transfer coefficient

\(I\) :

Intensity

\(I_{\text {max}}\) :

Maximum intensity

\(M\) :

Mach number

\(R\) :

Rotor radius (m)

\(r\) :

Radial coordinate (m)

\(R_{{\text {cam}}}\) :

Radial position of the camera (m)

\(Re\) :

Reynolds number

\(St\) :

Stanton number

\(t\) :

Thickness (m)

\(t_{\text {max}}\) :

Maximum airfoil thickness (m)

\(v_\infty \) :

Freestream velocity (m/s)

\(v_{\text {max}}\) :

Maximum velocity (m/s)

\(v_{{\text {min}}}\) :

Minimum velocity (m/s)

\(v_{{\text {tip}}}\) :

Rotor blade tip speed (m/s)

\(x\) :

Chordwise coordinate (m)

\(z\) :

Vertical coordinate (m)

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Acknowledgments

The authors would like to thank S. Kalow and J. Riemenschneider of the Institute of Composite Structures and Adaptive Systems of the DLR in Braunschweig for their support in performing the whirl tower test. For the conduction of the tests with the DLR helicopters, the authors would like to thank T. Wilmes and U. Göhmann of the DLR Facility for Flight Experiments in Braunschweig.

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  1. German Aerospace Center (DLR), Bunsenstr. 10, 37073 , Göttingen, Germany

    K. Richter & E. Schülein

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  1. K. Richter
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  2. E. Schülein
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Correspondence to K. Richter.

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Richter, K., Schülein, E. Boundary-layer transition measurements on hovering helicopter rotors by infrared thermography. Exp Fluids 55, 1755 (2014). https://doi.org/10.1007/s00348-014-1755-z

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