Development and validation of a single degree of freedom perforate impedance model under high SPL and grazing flow

Leonardo I4N research program – design of novel acoustic liners for aero engine nacelles

“…The studies have led to the development of a number of low weight novel liner configurations of varying complexity which are predicted to show improved broadband attenuation when compared to that realised for traditional designs. Work has included the development and validation of acoustic liner impedance models [1], liners with porous cell walls and cells which are considerably wider than traditional designs [2], and the design and manufacture of novel liners with complex cavities (replacing traditional straight cavities) [3,4]. The attenuation potential of the novel designs is improved further by increasing the integrity of duct liner attenuation modelling Materials Research Proceedings 37 (2023) 6-9 https://doi.org/10.21741/9781644902813-2 7 significantly, in particular by using a more representative source content and by including the influence of boundary layer refraction at the duct walls [5].…”

“…Development and validation of a single degree of freedom perforate impedance model under high SPL and grazing flow Normal incidence impedance, grazing flow in-situ impedance, and insertion loss testing of a range of Single Degree-Of-Freedom (SDOF) perforates was performed, along with insertion loss tests on a complex cavity panel with varying cell widths and path lengths [1]. Grazing flow measurements, performed in the Santa Catarina grazing flow facility in Brazil, acquired liner impedance and attenuation data at Mach numbers up to 0.6, and at SPLs up to 155dB.…”