Bypass Duct Acoustic Liner Design With and Without Bifurcation Effects
The growth in air traffic and the commitment to sustainable aviation continue to provide new challenges to reducing aircraft noise levels. Acoustic liner design methodologies must therefore provide the capability to efficiently predict the acoustic benefits of novel liner configurations within complex aircraft nacelle geometries. With these observations in mind, a broadband acoustic liner optimization process has been developed and assessed through a series of design and experimental studies at increasing technology readiness levels. This work applies the design process to the aft-fan noise component and explores the effects of bypass duct bifurcations (e.g., the pylon and lower bifurcation). In addition to this new application, the design study is expanded to include the use of a commercially available duct propagation code. Despite the different general workflow for the two propagation codes, consistent optimized impedance spectra and in-duct attenuation predictions were obtained for several acoustic treatment options. The preliminary results are promising, and this work increases confidence in the enhanced broadband liner design methodology and lays the groundwork for complimentary use of the codes in future studies. The potential benefits of acoustic treatment on the upper and lower bifurcations are also demonstrated. The knowledge gained through this preliminary stage of the liner design process will be used to guide the identification of candidate liner designs for a proposed static engine test within the next year.