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The University of Southampton
Engineering

Measurement

An open jet wind tunnel has been designed and built at the ISVR for the measurement of aerodynamic noise. A photograph of the nozzle situated in the ISVR’s 8 m × 8 m anechoic chamber is shown.

The facility has low noise and turbulence, as indicated in the figures below.

Variation of turbulence intensity through the jet.

Comparison of background noise levels of the rig with other open jet wind tunnel. Results normalised to the same nozzle area.

Excellent comparison between the measured and predicted sound pressure level spectrum for a NACA12 airfoil in a uniform flow and that obtained using the Brookes predictions scheme is presented here for various jet velocities. Jet mixing noise is seen to dominate at low frequencies.

Measurements of the sound pressure level self-noise spectrum from a NACA0012 airfoil obtained versus jet velocity, at a microphone at 90 degrees to the trailing edge. The lines show the variation of the tonal frequencies due to TS waves and its classical ‘ladder’ behaviour.

Airfoil Noise Control

A study is underway (FLOCON) aimed at the investigation of low noise technologies for reducing airfoil self noise. One of these technologies is serrations, a number of which are shown opposite.

The measured sound pressure level reduction versus frequency and jet velocity for serrated trailing edge noise geometry is shown. As well as significant reductions in trailing edge noise (in this low Reynolds number example), there is also significant noise increases due to vortex shedding caused by bluntness.




 

ISVR’s open jet wind tunnel.
Different trailing edge serration geometries tested in a study of low noise trailing edge geometries.
Trailing edge serration geometries
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