Optimisation of silencers for noise and pollution reduction

Supervisors

• Cédric Maury, Professor ECM, Laboratory of Mechanics and Acoustics, Marseille, France.
  cedric.maury@centrale-marseille.fr
  https://laboratoire-mecanique-acoustique.fr/membre/67-cedric-maury
• Teresa Bravo, CSIC Tenure Researcher, Consejo Superior de Investigaciones Cientificas, Madrid, Spain. teresa.bravo@csic.es
  https://www.itefi.csic.es/en/staff/bravo-maria-teresa

Funding: A*Midex Fundation (Aix-Marseille University - AMU)
Duration: 6 months as from February 2027 

Background
This internship is part of the AERMES (A*Midex, AMU) and AEROSMEET (CSIC) collaborative research projects between the LMA and CSIC laboratories. The M2 project aims to develop new generations of noise-reducing and depolluting silencers [Fig. 1a] able to achieve broadband noise attenuation with minimum embarked mass, and slow sound to agglomerate fine particles [1]. Potential applications include noise pollution reduction and clean air in ground transportation and aeronautics.

Figure 1: (Left) Example of a microperforated “rainbow” silencer [1]; (centre) sound-absorbing structure based on an “acoustic black hole” (ABH), with cavities of increasing depth; (right) topologically optimised ABH for perfect sound absorption [2].

Topology optimization is a powerful design approach that determines the optimal distribution of material within a given domain to maximize or minimize a specific physical quantity, such as the acoustic pressure level at the outlet of a silencer. Starting from a simple initial geometry, the algorithm identifies regions where material should be retained or removed, subject to constraints such as volume, mass, minimum feature size and manufacturing requirements. For instance, in room acoustics, topology optimization can be used to determine an optimized wall geometry [3] that reduces noise levels in a specific region of the room [Fig. 2].

Figure 2: (left) Acoustic mode in a rectangular room; (right) spatial redistribution of the acoustic mode following topology optimization of the upper wall, resulting in a reduction in sound pressure level within the circular region at the bottom right [3].

Objectives

The objective of this internship is to numerically investigate, using COMSOL Multiphysics, the topology optimization of an open acoustic black hole (ABH) silencer to maximize its visco-thermal energy dissipation over a frequency band and achieve slow sound effect. The robustness of the silencer's acoustic performance will be assessed under airflow velocities of up to 30 m/s. The resulting optimized configurations will be analysed and their underlying physical mechanisms interpreted. Additive manufacturing and wind-tunnel measurements of the silencers properties are also envisaged.

Work plan – Expected outcomes:

• Getting familiar with topology optimization tools: Use COMSOL tutorials to optimize the walls of an acoustic room [Fig. 2] through COMSOL Class Kit.
• Topology optimization of a 2D silencer geometry: (1) maximize dissipation and sound level reduction and (2) slow down sound propagation.
• Comparison of optimized geometries and analysis of the physical mechanisms.
• CAD model extraction and additive manufacturing by a technical service.
• Measurements of the aeroacoustic performance of the optimized silencers.

Prerequisites and required skills:

• Acoustics and fluid mechanics.
• Numerical methods in acoustics.
• Experience in computer-aided design (CAD) would be an advantage

Skills and expertise acquired:

• Numerical modelling of fluid flows and their coupling with acoustics.
• Training in topology optimization, a technique widely used in industrial applications.
• Experience with a complete end-to-end design workflow, from numerical modelling to 3D printing and experimental testing.
• Research experience in sound-slowing structures and slow-sound propagation.

[1] C. Maury, T. Bravo and F. Ali, Micro-perforated rainbow-trapping silencers with broadband sound dissipation and reduced drag under low-speed grazing flow, Journal of Sound and Vibration, 616, 119228 (2025).

[2] A. Mousavi, M. Berggren, L. Hägg, E. Wadbro, Topology optimization of a waveguide acoustic black hole for enhanced wave focusing. Journal of the Acoustical Society of America, 155, 742–756 (2024).

[3] COMSOL tutorial: Topology Optimization of an Acoustic Mode in a 2D Room.