详情

原文传递 Fundamental Study of Bifurcation Acoustic Treatment Effects on Aft-Fan Engine Noise.

题名：	Fundamental Study of Bifurcation Acoustic Treatment Effects on Aft-Fan Engine Noise.
作者：	Nark, D. M; Jones, M. G.
摘要：	Increasing air traffic and more stringent aircraft noise regulations continue to expand requirements on aircraft noise levels. A major component of the overall aircraft noise is the sound associated with the propulsion system mounted in the engine nacelle. Acoustic liners mounted in the aircraft engine nacelles provide a significant portion of the current fan noise reduction. However, they must be further optimized if challenging noise reduction goals are to be achieved. One location within the aft bypass duct that may be an excellent candidate for increased attention is the acoustic treatment on the engine bifurcations (i.e., engine pylon and lower bifurcation). This paper presents the continuation of a fundamental study of the effects of bifurcation treatment on simulated aft fan noise and the validation of numerical tools to predict such effects. Overall, five bifurcation configurations (two of which are the focus of this portion of the investigation) were fabricated and tested in the NASA Langley Curved Duct Test Rig. Impedance predictions for slotted core liner configurations were improved by using an “effective” depth in the liner models. Propagation predictions based on these impedances show that mode scattering may occur due to both the presence of the bifurcation, as well as variable impedance distributions on the bifurcation surface. One and two zone optimizations have been performed and results provide further evidence that the computation of an effective impedance is appropriate when the distinct chambers (chambers that provide a unique impedance) are confined within a spatial extent that is no larger than one-third of a wavelength for the highest frequency of interest. These initial results are promising and this work provides valuable information for further study and improvement of bifurcation acoustic treatments.
总页数：	12 pages