Optimisation of slanted septum core and multiple folded cavity acoustic liners for aero-engines

Abstract

This paper reports an assessment of the performance of two novel broadband liners for aero-engine applications, under both high sound pressure level and grazing flow. Duct insertion loss predictions are made for the novel liners for downstream sound propagation, with the results compared with that of optimised conventional Single Degree-of-Freedom (SDOF) perforate liners. The novel liner configurations include a slanted porous septum concept with varying open area, and a MultiFOCAL (Multiple FOlded CAvity Liner) concept. A numerical model of the flow duct test facility is developed using the commercial finite element code, COMSOL Multiphysics. This model is used to predict the liner insertion loss in the flow duct test facility. A multi-modal sound source is used, employing the assumption of uncorrelated modes with equal energy per mode. For downstream sound propagation, a simple convected wave equation model with the standard Ingard–Myers boundary condition is shown to be sufficient to predict the liner attenuation accurately. For upstream sound propagation, predictions and measurements for a SDOF linear liner highlight the need to account for boundary-layer refraction in the numerical modelling. The refraction effect due to the mean flow boundary layer will be modelled in a follow-up paper.

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Identifiers

ORCID for Suresh Palani: orcid.org/0000-0003-0123-7635

ORCID for Alan McAlpine: orcid.org/0000-0003-4189-2167

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