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Measurement of the noise generation at the trailing edge of porous airfoils

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Abstract

Owls are commonly known for their quiet flight, enabled by three adaptions of their wings and plumage: leading edge serrations, trailing edge fringes and a soft and elastic downy upper surface of the feathers. In order to gain a better understanding of the aeroacoustic effects of the third property that is equivalent to an increased permeability of the plumage to air, an experimental survey on a set of airfoils made of different porous materials was carried out. Several airfoils with the same shape and size but made of different porous materials characterized by their flow resistivities and one non-porous reference airfoil were subject to the flow in an aeroacoustic open jet wind tunnel. The flow speed has been varied between approximately 25 and 50 m/s. The geometric angle of attack ranged from −16° to 20° in 4°-steps. The results of the aeroacoustic measurements, made with a 56-microphone array positioned out of flow, and of the measurements of lift and drag are given and discussed.

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Abbreviations

c :

speed of sound

c l :

chord length

d :

specimen thickness

D :

nozzle diameter

f :

frequency

F d :

drag force

F l :

lift force

Ma:

Mach number

OSPL:

overall sound pressure level

p :

sound pressure

PSD:

power spectral density

r :

flow resistivity

\(Re_{c_l}\) :

(chord based) Reynolds number

SPL:

sound pressure level

Sr:

(chord based) Strouhal number

Tu:

turbulence intensity

u :

turbulent velocity fluctuations

U :

free stream velocity

v :

flow velocity through porous sample

x jet :

length of the core jet

α:

geometric angle of attack

αeff :

effective angle of attack

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Acknowledgments

This research was sponsored by the Deutsche Forschungsgemeinschaft in the priority program 1207, “Strömungsbeeinflussung in der Natur und Technik”, under the grant numbers SA 1502/1-1 and SA 1502/1-2.

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Authors and Affiliations

  1. Aeroacoustics Group, Brandenburg Technical University of Cottbus, Siemens-Halske-Ring 14, 03046, Cottbus, Germany

    T. Geyer, E. Sarradj & C. Fritzsche

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  1. T. Geyer
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  2. E. Sarradj
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  3. C. Fritzsche
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Correspondence to T. Geyer.

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Geyer, T., Sarradj, E. & Fritzsche, C. Measurement of the noise generation at the trailing edge of porous airfoils. Exp Fluids 48, 291–308 (2010). https://doi.org/10.1007/s00348-009-0739-x

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  • DOI: https://doi.org/10.1007/s00348-009-0739-x

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