Experiments in Fluids

, Volume 48, Issue 2, pp 291–308

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

Research Article
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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.

List of symbols

c

speed of sound

cl

chord length

d

specimen thickness

D

nozzle diameter

f

frequency

Fd

drag force

Fl

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

xjet

length of the core jet

α

geometric angle of attack

αeff

effective angle of attack

Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  1. 1.Aeroacoustics GroupBrandenburg Technical University of CottbusCottbusGermany

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