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Investigation of wave phenomena on a blunt airfoil with straight and serrated trailing edges

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Abstract

An investigation of pressure waves in compressible subsonic and transonic flow around a generic airfoil is performed in a modified shock tube. New comprehensive results are presented on pressure waves in compressible flow. For the first time, the influence of trailing edge serration will be examined in terms of the reduction in pressure wave amplitude. A generic airfoil is tested in two main configurations, one with blunt trailing edges and the other one with serrated trailing edges in a Mach number range from 0.6 to 0.8 and at chord Reynolds numbers of 1 × 106 < Re c < 5 ×106. The flow of the blunt trailing edge is characterized by a regular vortex street in the wake creating a regular pattern of upstream-moving pressure waves along the airfoil. The observed pressure waves lead to strong pressure fluctuations within the local flow field. A reduction in the trailing edge thickness leads to a proportional increase in the frequency of the vortex street in the wake as well as the frequency of the waves deduced from constant Strouhal number. By serrating the trailing edge, the formation of vortices in the wake is disturbed. Therefore, also the upstream-moving waves are influenced and reduced in their strength resulting in a steadier flow. An increasing length of the saw tooth enhances the three dimensionality of the structures in the wake and causes a strong decrease in the wave amplitude.

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Abbreviations

a,b :

Semi-axis of ellipse (mm)

c :

Chord length (mm)

d :

Trailing edge thickness (mm)

f :

Frequency (kHz)

2h :

Length of saw tooth (mm)

\(M_\infty\) :

Free stream Mach number

\(M_W\) :

Absolute Mach number of a wave

p :

Pressure (bar)

\(p_\infty\) :

Free stream pressure (bar)

\(\Delta p\) :

Pressure amplitude (bar)

\(Re_c\) :

Chord Reynolds number

\(Re_d\) :

Reynolds number based on trailing edge thickness

SPA :

Scaled pressure amplitude

\(St_d\) :

Strouhal number based on trailing edge thickness

\(St^*_d\) :

Modified Strouhal number based on trailing edge thickness

t :

Time (ms)

\(U_\infty\) :

Free stream velocity (m/s)

x :

Coordinate of x-axis (m)

y :

Coordinate of y-axis (m)

\(\alpha\) :

Angle of attack (1°)

\(\beta\) :

Deflection angle (1°)

\(\delta\) :

Boundary layer thickness (mm)

\(\delta ^*\) :

Displacement thickness (mm)

\(\varphi\) :

Sawtooth angle (1°)

\(\varphi\) :

Phase angle (rad)

\(\sigma\) :

Standard deviation (bar)

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Acknowledgments

This research was funded by the German Research Foundation within the project “Numerische und experimentelle Untersuchung zur Abschwächung stromauf laufender Druckwellen bei transsonischer Profilumströmung” (DFG OL 107/22). The use of computer resources provided by the Jülich Supercomputing Centre (JSC) is also gratefully acknowledged.

Conflict of interest

The authors declare that they have no conflict of interest.

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Authors and Affiliations

  1. Shock Wave Laboratory, RWTH Aachen University, 52056, Aachen, Germany

    Juliane M. Nies, Manuel A. Gageik, Igor Klioutchnikov & Herbert Olivier

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  1. Juliane M. Nies
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  2. Manuel A. Gageik
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  3. Igor Klioutchnikov
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  4. Herbert Olivier
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Correspondence to Juliane M. Nies.

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Nies, J.M., Gageik, M.A., Klioutchnikov, I. et al. Investigation of wave phenomena on a blunt airfoil with straight and serrated trailing edges. Exp Fluids 56, 136 (2015). https://doi.org/10.1007/s00348-015-2009-4

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