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Unsteady surface pressures measured at a pitching Lambda wing with vortex dominated flow and transonic effects

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Abstract

In the Transonic Wind Tunnel Göttingen, pitch oscillations were performed with a Lambda wing to study unsteady pressure distributions of vortex dominated flow including transonic effects. The free stream Mach number was varied between 0.3 and 0.7. Small pitching amplitudes of \(0.08^{\circ }\)–\(0.4^{\circ }\) at excitation frequencies up to 40 Hz were used. In this paper, particularly the data of unsteady Pressure Sensitive Paint measurements and unsteady pressure sensors are analyzed. With increasing angle of attack, a suction peak and a shock occur near the leading edge. Then a shock-induced separation triggers the development of a vortex at the main wing. The unsteady pressures show: for lower angles of attack, the transonic influences are dominant. For higher angles of attack, the influence of the vortex becomes of similar magnitude and dominates the behavior of the pressure variations. The shock exhibits, with increasing angle of attack, an inverse motion. For angles of attack beyond the maximum lift, the unsteady pressure distributions and the lift show a significant phase lag, already at very low oscillation frequencies. Compared to subsonic cases, the supersonic region shifts the vortex induced pressures downstream.

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Abbreviations

\(\alpha\) :

Angle of attack

\(\Delta\) :

Difference, amplitude

\(\omega ^*\) :

Reduced frequency \(= 2\pi f c_{\mathrm{ref}}/U_\infty\)

\(\Phi\) :

Phase angle

c :

Chord length

\(c_\mathrm{l}\) :

Lift coefficient

\(c_\mathrm{m}\) :

Moment coefficient

\(c_\mathrm{p}\) :

Pressure coefficient

\(c_{\mathrm{p},\alpha }\) :

Unsteady pressure coefficient i.e. H(\(f_{\mathrm{ex}}(\alpha )\))

f :

Frequency

iPSP:

Unsteady Pressure Sensitive Paint

x, y, z :

Coordinates

CFD:

Computational fluid dynamics

FEM:

Finite element method

H :

Transfer function

Im:

Imaginary part

IWEX:

German: unsteady vortex experiment

Ma :

Mach number

PIV:

Particle Image Velocimetry

Re :

Reynolds number or real part

TWG:

Transonic wind tunnel Göttingen

\(_N\) :

Normal to leading edge sweep

\(_{\mathrm{ex}}\) :

Excitation

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Acknowledgements

The author would like to thank the team members of the Institute of Aeroelasticity, of the Institute of Aerodynamics and Flow Technology, SHT and the DNW-TWG contributing to the tests. Further acknowledgment goes to the German MoD and The Federal Office of Bundeswehr Equipment, Information Technology and In-Service Support (BAAINBw) for their support of the DLR project.

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Authors and Affiliations

  1. DLR, Institute of Aeroelasticity, Bunsenstrasse 10, 37073, Göttingen, Germany

    Stefan Wiggen & Johannes Nuhn

  2. DLR, Institute of Aerodynamics and Flow Technology, Göttingen, Germany

    Ulrich Henne, Christian Klein & Werner Sachs

Authors
  1. Stefan Wiggen
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  2. Ulrich Henne
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  3. Christian Klein
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  4. Johannes Nuhn
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  5. Werner Sachs
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Corresponding author

Correspondence to Stefan Wiggen.

Additional information

Paper based on presentation at CEAS 2015 conference, 7th–11th Sept., Delft, The Netherlands.

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Wiggen, S., Henne, U., Klein, C. et al. Unsteady surface pressures measured at a pitching Lambda wing with vortex dominated flow and transonic effects. CEAS Aeronaut J 9, 417–427 (2018). https://doi.org/10.1007/s13272-018-0293-4

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  • DOI: https://doi.org/10.1007/s13272-018-0293-4

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