Broadband and Low-Frequency Acoustic Liner Investigations at NASA and ONERA
Michael G. Jones, Frank Simon, Rémi Roncen
Abstract
NASA and ONERA have explored a number of acoustic liner concepts over the last few decades. This paper begins with a brief review regarding conventional liners as well as the recent implementation of multi-degree-of-freedom liners enabled by embedded mesh caps. Six novel liner concepts are presented, along with the accompanying impedance prediction models used in their design. Each of the NASA concepts is designed to vary the impedance over the surface of the liner in a controlled manner, whereas the ONERA concepts make use of long neck acoustic resonators. Selected results are presented for each of these liners evaluated in the NASA and ONERA test rigs. Finally, a set of aeroacoustic metrics is defined for comparison standardization between conventional and innovative acoustic liners and all the concepts are compared on this basis.