Acoustic Research       

Recently, a series of wind tunnel tests were conducted using phased microphone arrays. A phased microphone array is composed of multiple microphones arranged in an optimized pattern. The signals from each microphone are sampled and then processed in the frequency domain. The relative phase differences seen at each microphone determine where noise sources are located. The amplification capability of the array allows detection of noise sources well below the background noise level. This makes microphone arrays particularly useful for wind tunnel evaluations of airframe noise since, in most cases, the noise produced by wings, flaps, struts and landing gear models will be lower than that of the wind tunnel environment.

A microphone array installed in the wall of the NASA Ames 7- by 10-Foot Wind Tunnel. The array can image the bottom of the installed wing/flap model.

An acoustic array image of a wind tunnel model of a DC-10 showing aerodynamic noise sources at the slats and flaps of the wing.

A 1000 Hz acoustic array image of a Corvette driving by at 30 mph. The lower source is from the engine. The source in the window is a test speaker.