PhD - Inverse modal identification of free-field radiated noise from unducted rotor-stator stages: from laboratory arrays to Open Fan flight tests

Context:

This postdoctoral position is part of the European project TAKE-OFF (Clean Aviation programme), which is preparing the full-scale flight demonstration of Safran Aircraft Engines’ RISE Open Fan engine on the Airbus A380 flying testbed, with the aim of reducing fuel consumption by 30 % and entering service around 2035. Without a nacelle, the engine noise sources radiate directly into free field. LMFA (École Centrale de Lyon), in collaboration with LVA (INSA Lyon), is in charge of analysing the near-field pressure data acquired in flight by microphones installed on the fuselage, in order to reconstruct the engine noise sources.

Objective:

To extend the modal analysis methods developed at LMFA for ducted engines [1] to unducted fans. For the first time, modal analysis will be applied to microphones located in an unconfined medium and to modes radiating under free-field conditions, and design criteria specific to this configuration will be established (spatial sampling, resolution, array-to-rotor distance relative to the array size).

Description:

Task 1 – Model and inverse problem. Build a set of eigenfunctions describing the radiation of an unducted rotor-stator stage (spinning modes weighted by Bessel functions [2], spherical harmonics, etc.) and embed it in a Bayesian inverse approach [1] to estimate the modal amplitudes of tonal and broadband components. Flow and fuselage effects may be accounted for through CAA computations.

Task 2 – Validation on the MAMBO database. The developments will be tested on an unducted propeller + stator configuration recently studied at LMFA (MAMBO project), instrumented with three arrays: a half-cylindrical array, a planar array on the side (representative of fuselage instrumentation) and a motorised arc array measuring directivity, which will serve as an independent reference. This study will assess the robustness of the method and define array design criteria.

Task 3 – Application to flight tests. The methodology will be applied to the near-field pressure data acquired on the fuselage during the TAKE-OFF flight test campaigns, in order to identify the modal content of the noise radiated by the Open Fan engine and to infer information on its generation mechanisms.

Starting date : 01/01/2027

Profile and application:

PhD in acoustics, aeroacoustics or signal processing; skills in array methods, inverse problems and/or modal analysis; scientific programming (Python/Matlab).

References:

[1] Pereira, A. & Jacob, M.C., 2022, Modal analysis of in-duct fan broadband noise via an iterative Bayesian inverse approach, J. Sound Vib., doi:10.1016/j.jsv.2021.116633.

[2] Roger, M. & Kucukcoskun, K., 2019, Near-and-far field modeling of advanced tail-rotor noise using source-mode expansions, J. Sound Vib., 453, 328-354.

LMFA contacts: Antonio Pereira, Marc Jacob

LVA contact: Quentin Leclère (LVA, INSA Lyon)

Funding: European project TAKE-OFF (Technology and Knowledge for European Open Fan Flight)

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