Experimental and numerical assessment of novel acoustic liners for aero-engine applications

Abstract

In this paper the performance of two novel broadband liners for aero-engine applications is assessed in the presence of both high sound pressure level and grazing flow. The novel liner configurations include a slanted porous septum concept with varying percentage open areas, and a MultiFOCAL (MULTIple FOlded CAvity Liner) concept. In-duct liner insertion loss predictions and measurements for both downstream and upstream sound propagation are presented, with the results compared to an optimised conventional single-degree-of-freedom perforate liner. Both the novel liners are predicted and measured to provide improved broadband attenuation for downstream propagation, with excellent agreement seen between the measurement and prediction. For downstream sound propagation, a uniform flow model (Convected Wave Equation) with the standard Ingard–Myers boundary condition is shown to predict the liner attenuation accurately, indicating that the boundary effects can be neglected for the downstream case. For upstream sound propagation, the insertion loss predictions and measurements highlight the importance of accounting for boundary-layer refraction in the numerical modelling. Thus, the Linearised Euler equations are used to model the effect of the boundary layer on the predicted liner attenuation for upstream propagation.

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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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