Inlet Acoustic Treatment for Interior Noise Control

An investigation is made of interior noise in a medium size rear engine turbofan business jet attributable to multiple pure tone and blade passage frequency acoustic radiation from the inlet. The purpose is fourfold; to quantify interior noise levels and identify broadband noise and tonal noise sources, to identify the transmission path of inlet radiated noise, to construct an approximate technique to predict the effect of inlet acoustic treatment targeted to tonal noise on interior noise, and to demonstrate improvement in interior noise achievable by inlet acoustic treatment. The project includes ground and flight testing, design of acoustic treatment, a simplified development of a transfer function for prediction of transmission of inlet radiated noise to the interior, and predi ction of interior noise levels. Useful attenuation of tonal noise is shown to be achievable with improvement in one-third octave band levels above 1000 Hz and in Speech Interference Level. © 2007 by David R. Burd