Instrumentation

NASA Glenn Research Center researchers are diligently preparing for upcoming moonwalk simulations using advanced instrumentation. Specialized tools such as particle image velocimetry, hot wire anemometry, Raman spectroscopy, and phased array microphones are being employed to measure airflow and sound. These measurements are crucial for validating theories and noise prediction software relevant to global aviation noise reduction efforts.

One key piece of equipment is the Rotating Rake Mode Measurement System (RRMS). This system utilizes rotating microphones to capture data from tones emitted by turbofan engines. Traditional stationary microphones fall short in this regard, necessitating the pioneering techniques developed by NASA Glenn engineers in the 1990s. RRMS has been utilized in various tests, from low-speed proof of concept experiments to full-scale turbofan engine evaluations.

Another innovative approach involves phased array microphone systems. By arranging microphones in 1D, 2D, or 3D configurations, researchers can pinpoint noise sources with precision. NASA Glenn's Array48 system has been instrumental in identifying noise sources within scale-model jet flows, counter-rotating open rotor fan models, and even full-scale military engines.

Additionally, microphones embedded in an engine's fan duct enable the determination of noise source locations on rotating blades, a development funded by NASA.

To accurately measure the air velocity around experimental propulsors, NASA employs hotwire probes and Laser Doppler Velocimeters (LDV). These instruments provide detailed velocity measurements upstream, downstream, and between the rotor and stator. Analyzing the resulting plots allows researchers to visualize disturbances caused by the rotor, which in turn aids in identifying noise sources and developing strategies to mitigate them.

Such velocity data is routinely utilized to validate calculations estimating noise from turbofan engines.