Active Acoustic Metamaterial Based on Helmholtz Resonators to Absorb Broadband Low-Frequency Noise

The aim of the present work is to design active acoustic metamaterial consisting of an array of Helmholtz resonators and fabricating them using an additive manufacturing technique in order to assist in a reduction in noise levels in aerospace applications. To this aim, initially, a passive metamaterial consisting of an array of 64 Helmholtz...

Designing a resonant panel based on Helmholtz resonators with reduced geometrical complexity

Acoustics combined with digital fabrication has been investigated for multiple years. Most research in this area has focused on the combination of acoustics and additive manufacturing. This is mainly due to the ability of this technique to create any geometry, which allows for very high absorption. However, it has the downside that additive...

Inner-Scaled Helmholtz-Resonators for Turbulent Boundary Layer Flow Control

An experimental study is presented towards inner-scaled Helmholtz-Resonators (HRs) as a passive turbulent boundary layer (TBL) flow control method. Using acoustic pressure-velocity coupling at the orifice of the HR, it is aimed to attenuate the kinetic energy of the grazing turbulence to reduce the mean skin friction. The HRs are tuned towards...

Acoustic liners for jet-installation noise reduction

A Helmholtz resonator with a curved cavity is studied for reducing jet-installation noise in a configuration comprised by a subsonic jet and a nearby flat plate. The face-sheet and cavity are designed with the Guess method and the impedance is verified through an experiment and a simulation of an impedance tube. Both single and double degree...

Numerical Study on the Occurrence and Sensitivity of a High-Frequency Instability in an Advanced Can-Annular Combustion System

Gas turbines for power generation use lean premixed flames to adhere to the strict pollutant emissions regulations. Unfortunately, this often leads to thermoacoustic instabilities. These instabilities can lead to failure of system components, flame blow-off or flashback and a reduction in efficiency. Especially the high frequency transverse...

Application of Acoustic Metamaterials in Boundary Layer Instability Control

To achieve delay of laminar-to-turbulent transition of boundary layers, the application of acoustic metamaterial concepts is investigated. This is done analytically, numerically and experimentally by studying the interaction between a Helmholtz resonator and a TS wave. A Helmholtz resonator can serve as a meta-atom in a metamaterial. The desired...

Pneumatically-actuated acoustic metamaterials based on helmholtz resonators

Metamaterials are periodic structures which offer physical properties not found in nature. Particularly, acoustic metamaterials can manipulate sound and elastic waves both spatially and spectrally in unpreceded ways. Acoustic metamaterials can generate arbitrary acoustic bandgaps by scattering sound waves, which is a superior property for...

Resistance in Helmholtz Resonators: Exploring the potential of sound absorption created by additive manufacturing

This research aims at improving the performance of Helmholtz resonators by adding resistance using additive manufacturing. Current use of Helmholtz resonators is focused on tonal applications and modal issues, because of the frequency specific behaviour. A normal Helmholtz resonator curve has a decreasing bandwidth when the peak increases. The...

Evaluation of the applicability of Helmholtz resonators for low frequency acoustic liners

A literature study has been carried out on the acoustic behaviour of those Helmholtz resonator type liners which are most promising for low frequency sound absorption in aero-engine applications. The equations for the acoustic impedance of various types of Helmholtz resonators have been analyzed as well as the conditions for the validity of...