NASA Glenn Uses Rotating Microphones to Map Aircraft Noise

NASA Glenn Research Center teams use specialized instruments to measure airflow and sound in research experiments. Their toolkit includes particle image velocimetry, hot-wire anemometry, Raman spectroscopy, phased microphone arrays and rotating microphone rakes.

NASA Glenn developed rotating-microphone procedures in the 1990s to measure acoustic modes that stationary microphones cannot capture.

What has been confirmed

NASA Glenn engineers developed rotating-microphone procedures in the 1990s to measure acoustic modal content that stationary microphones cannot capture. Researchers have used rotating microphone rakes in the Advanced Noise Control Fan Rig, the 9- by 15-Foot Low Noise Wind Tunnel and full-scale turbofan engine ground tests. NASA Glenn’s Array48 phased microphone system has located sound sources in scale-model jet flows, a counter-rotating open-rotor fan model and a full-scale F404 military engine. A NASA-funded approach also places microphones inside an engine fan duct to locate sound sources on rotating blades.

Why it matters

Research teams use hot-wire probes and laser Doppler velocimeters to measure airflow before, after and between a propulsor’s rotor and stator. Those measurements help researchers examine airflow disturbances and check calculations used to predict turbofan noise. NASA Glenn experiment data also help the aviation noise-reduction community validate theories and noise-prediction software.

FlyMarshall context

For airline passengers, engine-noise research connects to the sound heard around airports and in aircraft cabins. Microphone arrays help researchers identify where sound originates, while airflow measurements show how moving air interacts with rotating engine components. These tools give engineers data to assess noise-reduction ideas before applying them to commercial aviation.

What happens next

NASA’s published information describes the instruments, test configurations and research uses; it does not identify a timeline for a specific commercial-aircraft application.