Development of novel, light-weight and multifunctional acoustic metamaterials/metasurfaces for aeronautical applications using 3D Boundary Element Method (BEM3D)

Low cost airlines have significantly increased the air transport, thus increase in aviation noise [1]. Conventional noise attenuation techniques cannot mitigate civil aviation noise. The aim of this work is to design innovative configurations, which are capable of absorbing, dissipating and redirecting the aero-noise at the source. To achieve this, the light-weight multi-functional acoustic metamaterials and metasurfaces those have already been proven in room acoustics and noise attenuation are being studied to test their performance in flow and modify their design to be suitable for aeronautical applications [2], [3]. Sound propagation through aero-engines which involves moving sources in moving media provides a significant challenge in predicting as conventional methods are not applicable. The work presented here considers the development and re-formulation of existing techniques to incorporate the aeroacoustic environment and to validate results with experimental data. To achieve this, a 3D Boundary Element Method being developed, which is a standard colloction technique that can optionally use the Fast Multipole Method (FMM) library of Greengard and Zimbutas [4] to simulate aero-acoustic problems. The sound propagation in mean flow is solved using the Taylor Transformation [5]. In particular, scattering problems are solved by applying Taylor’s transformation to the solution for the total field in the zero-flow case, as in the work of Agarwal and Dowling [6]. Furthermore, the metamaterials are being implemented as an impedance patch, by extracting the characteristic parameters. Non-local boundary conditions are being implemented in 3DBEM, which hales a significant leap in development of simulation method. This will allow a complete implementation of metamaterial as a non-locally reacting impedance patch in aero-acoustic environment. Initial experiments have been carried out inside windtunnel, which show reasonable agreement with 3DBEM predictions. This work is being extended to a wider range of acoustic metamaterials and metasurfaces in order to enhance the controllability and tunability of sound propagation over wide frequency bands in aeroacoustic environments.