Low Profile, Low Frequency, Adaptively-Tuned Acoustic Liner

Conventional approaches to aircraft engine noise reduction via passive acoustic liners are limited in performance, particularly at lower frequencies, where improvements are gained through increased liner depth. Typical engine nacelle installation clearances, however, limit liner depth and prevent further improvements in low frequency noise reduction using these conventional approaches. The proposed innovation addresses these limitations via a low-profile, tunable acoustic liner for modern aircraft engines capable of significant noise attenuation at lower frequencies than currently achievable. The innovative approach lowers the resonant frequency and enables significant reductions in cavity size and volume. Significant net weight savings is achieved due to the large reductions in cavity volume (via corresponding decreases in cavity wall surface area). The end result is lower frequency noise attenuation with simultaneous reductions in liner depth and weight. The proposed innovations provide the following benefits for acoustic noise reduction: ? Optimum absorption of sound at frequencies half of those achievable with currently available technologies ? Decreased liner depth ? Decreased liner weight ? In-situ, automatic tunability for optimum absorption under different engines and engine conditions. ? Broadband operation through MDOF performance and individual impedance tuning