Dissecting Tones Radiating from Aircraft Engine Inlet and Exhaust Ducts
Hear an annoying tone from your turbofan engine? Engineers might prescribe an advanced liner or specially tuned active noise control system to quiet it down.
To get it right, though, more information about the modal content of the tone is needed. This kind of data can’t be measured with a stationary microphone, which is why NASA Glenn engineers pioneered procedures using rotating microphones in the 1990s.
Rotating Microphone Rakes have been used by NASA Glenn researchers in a wide variety of tests ranging from low-speed proof of concept tests in the Advanced Noise Control Fan Rig and 9’ x 15’ Low Noise Wind Tunnel, to full-scale turbofan engine tests.
- “Interaction and scattered mode measurement in a mixed bypass/core duct with multiple rotating sources”, International Journal of Aeroacoustics, Vol 16, Issue 7-8, 2017, D.L. Sutliff.
- “Techniques for analyzing rotating rake mode measurements over passive treatment”, International Journal of Aeroacoustics, Vol 15, Issue 4-5, 2016, D.L. Sutliff and M.D. Dahl.
- “Turbofan Duct Mode Measurements Using a Continuously Rotating Microphone Rake”, International Journal of Aeroacoustics, Vol 6, Issue 2, 2007, D.L. Sutliff.