Abstract
An experimental campaign was carried out to assess recent acoustic modifications to the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel. This effort was undertaken in preparation for future rotorcraft, Advanced Air Mobility, and airframe noise acoustic tests. The tunnel is a closed circuit and typically operates in an open-jet configuration for acoustic studies. A vertical linear array of microphones and a phased array were placed on traverses outside of the core flow. Pole-mounted acoustic sources with known waveforms were used to identify sources of reflection under static conditions. A similar process was replicated with more compact sources in an aerodynamic fairing for flow speeds up to Mach 0.16. This allowed for acoustic characterizations of the test section core flow and bounding shear layer. Periodic averaging was investigated as a method for isolating acoustic sources and was shown to be capable of isolating periodic acoustic signals even for poor signal-to-noise ratio conditions. Benefits and limitations of single-microphone processing methods are identified. A companion paper utilizes a phased array in an effort to address the identified limitations to more traditional single-microphone data collection.
Published Version
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