Modelling the suppression of rotor-alone fan noise with Over-Tip-Rotor liners and comparison with measurements from a high-bypass turbofan rig

Palleja Cabre, Sergi, Tester, Brian and Astley, Jeremy (2021) Modelling the suppression of rotor-alone fan noise with Over-Tip-Rotor liners and comparison with measurements from a high-bypass turbofan rig. In AIAA AVIATION 2021 FORUM. (doi:10.2514/6.2021-2242).

Abstract

Fan noise is one of the dominant sources of aircraft engine noise, both at approach and at take-off. Improved attenuation of fan noise with acoustic liners and the reduction of fan noise at source remain key technology challenges for the foreseeable future. Over-Tip-Rotor (OTR) acoustic treatments have been investigated experimentally during the last decade and significant fan noise reductions have been measured, most recently at NASA using a single rotor and multiple lined circumferential grooves. This paper describes an analytical OTR prediction model in which the fan noise is modelled with point or distributed, static or rotating monopole and dipole sources based on Green’s functions for infinite hard or lined cylindrical ducts containing uniform mean flow; these are combined with an anechoic or unflanged inlet termination and an embedded finite length lined section representing the ‘rotor-alone’ source with its OTR liner. OTR liner insertion loss predictions are obtained for comparison with data from the W-8 NASA experimental rig yielding peak broadband in-duct noise reductions of up to 4 dB, in line with the measurements.

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Contributors

Author: Sergi Palleja Cabre

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