Acoustic Upgrades to Wind Tunnels at the National Research Council Canada

Abstract

Airframe noise is growing a concern for aircraft manufacturers, operators and communities. The ability to determine the location and strength of noise sources on an aircraft or its components allows noise reduction strategies to be developed which can have signicant impact on the overall noise signature of the aircraft. Phased-microphone array measurement technologies have become an eective tool in noise source localization for aerospace congurations. With the growing national need to address airframe noise issues, the National Research Council Canada upgraded two of its wind tunnels to provide a better acoustic environment to make phased-array measurements. The rst facility to be upgraded in 2009 was the 0.9m 3/4-open jet low speed research tunnel in which the original metal turning vanes on the corners bounding the test section were replaced with vanes lined with acoustic foam. This reduced the background noise in the test section by 5 - 10dB depending upon the frequency with little reduction in maximum tunnel speed. The second facility to receive an acoustic treatment was the 2m x 3m closed circuit tunnel in 2011. For this facility, an acoustic liner was developed for the test section which allowed the microphones to be recessed out of the ow and decreased the reverberant nature of the hard-walled tunnel. All walls of the tunnel were covered with acoustic foam-lled boxes