Reduction of acoustic and aerodynamic noise through sustainable micro-pore absorbers

Land transport and aeronautical industries are currently faced with the challenge of the design of lightweight and compact acoustic materials capable of reducing under flow the low and medium frequency components (< 1 kHz) of surrounding noise sources. Current treatments for reducing internal and external noise are based on the use of acoustic resonators and porous materials whose effectiveness covers the medium and high frequency ranges. The search for passive acoustic treatments with low embarked mass and capable of reducing low frequencies remains an open problem. The general objective of the i-LINK+ Programme funded by the Spanish National Research Council (CSIC) is to stimulate the collaboration between national research groups and international research groups of the highest relevance in these fields. The domains of expertise for the LMA partner (Laboratory of Mechanics and Acoustics, France) are vibro-acoustics, fluid-structure coupling, and sound field synthesis. From the side of the ITEFI (Spain), they are experts in the active control of noise and vibration, the design and optimisation of micro-perforated insulating partitions, the wave propagation in metaporous media and the development of novel experimental methods in acoustics. Taking advance of the complementary capacities of both institutions, the objective of this collaboration project is to develop an innovative experimental methodology for the characterization of the acoustic attenuation properties of test materials in a test bench (without flow) and in a subsonic wind tunnel (under turbulent boundary layer). Non-intrusive measurements will be performed by Laser Doppler Velocimetry (VLD) to estimate the attenuation of acoustic pressure and velocity near test materials. They will be compared with measurements by nosecones microphones, hot-wire anemometry and pressure-velocity probes in order to define the field of application of the VLD method. Additional information may be obtained by Particle Imaging Velocimetry on the modification by the material of the structures present in the turbulent boundary layer.