Design and Test of Novel Aero Engine Inlet Liners at the AneCom AeroTest Facility – Part I, Predictions

This paper presents validated predictions of hard-walled and lined in-duct propagation and far-field radiation, for a set of traditional and innovative acoustic panels, tested at AneCom AeroTest Acoustic Facility within the scope of the Leonardo "I4N - Innovation for Nacelles" research programme. In particular, the paper investigates the impact of the distribution of the fan noise SPLs across upstream propagating circumferential and radial modes, along with the influence of turbulence-induced acoustic losses along the duct walls. A linear partition scheme for the distribution of sound pressure levels across the propagating radial modes is proposed, and it is validated against measurements at subsonic fan RPMs of 60% N1 and 80% N1. The inclusion of a radial distribution of amplitudes leads to significantly improved predictions of liner attenuation, while having a relatively small influence on the optimum impedance. The study also demonstrates that the turbulence-induced acoustic losses can be neglected for a fan RPM of 60% N1, while they should be included in the prediction of upstream sound propagation for a fan RPM of 80% N1. This paper complements previous work which included the impact of the measured fan source circumferential mode amplitudes and boundary layer refraction during the optimisation of the AneCom inlet liners.