Instrumentation

NASA's Glenn Research Center is conducting preparations for upcoming moonwalk simulations, utilizing special instrumentation to measure airflow and sound. The research teams employ various tools such as particle image velocimetry, hot wire anemometry, Raman spectroscopy, and phased array microphones. These measurements are crucial for validating theory and noise prediction software used by the global aviation noise reduction community.

One such instrument is the Rotating Rake Mode Measurement System (RRMS), which employs rotating microphones to capture data for quieter turbofan engines. Engineers have pioneered this method due to its ability to provide more information about the modal content of engine tones, which stationary microphones cannot detect. RRMS has been utilized in a range of tests, from small-scale proof of concept experiments to full-scale turbofan engine ground tests.

Phased array microphone systems are another key component in NASA's noise measurement arsenal. These systems consist of microphones arranged in various 1D, 2D, or 3D configurations. When the sound measurements from these microphones are processed correctly, they can pinpoint noise sources. NASA Glenn has developed an Array48 system that has been extensively used to locate noise sources in scale-model jet flows, counter-rotating open rotor fan models, and even full-scale military engines.

Furthermore, NASA's research into air velocity is essential for identifying noise sources within experimental propulsors. Specialized instrumentation like hotwire probes and Laser Doppler Velocimeters (LDV) are used to measure the air velocity upstream, downstream, and between the rotor and stator of the propulsor. This data enables engineers to visualize the disturbances created by the rotor and work towards mitigating them.

The velocity measurements, in turn, help validate calculations used to estimate noise from turbofan engines.