Acoustic wall treatments for wind tunnel aeroacoustic measurements

Mourão Bento, H.F.; Ragni, D.; Avallone, F.; Simons, D.G.; Snellen, M.

doi:10.1016/j.apacoust.2022.108989

Acoustic wall treatments for wind tunnel aeroacoustic measurements

Title

Acoustic wall treatments for wind tunnel aeroacoustic measurements

Author

Mourão Bento, H.F. (TU Delft Wind Energy)
Ragni, D. (TU Delft Wind Energy)
Avallone, F. (TU Delft Wind Energy)
Simons, D.G. (TU Delft Aircraft Noise and Climate Effects)
Snellen, M. (TU Delft Control & Operations)

Department

Control & Operations

Date

2022

Abstract

Sound absorbing porous materials are used to line a wind tunnel wall, in order to reduce reflections. However, the lining can have a detrimental effect on the acoustic measurements due to an increase in the noise radiated from the walls. In addition, the aerodynamic fidelity of the tunnel can be affected. In the present study, the influence of the porous materials on the boundary layer aerodynamic characteristics is assessed. The consequent aerodynamic noise scattering is also studied, and compared against the acoustic benefit from absorbing reflections in the test section. Geometric modelling is used to understand the influence of varying absorbing materials in reducing the acoustic interference caused by the reflections. The aerodynamic and acoustic results are related to the roughness, and to the viscous and inertial resistivities of the three porous materials studied. The material with highest roughness (polyester wool) is found to result in the strongest turbulent fluctuations in the boundary layer. However, it is the material with the thickest fibre diameter (PU foam), and consequent highest inertial resistivity, which generates the strongest surface noise scattering. Materials with high viscous resistivity, together with low inertial resistivity, are found to provide good sound absorbing capabilities. The results therefore indicate that the best choice of sound absorbing wall treatment for wind tunnel applications results from minimizing roughness and inertial resistivity, while maximizing viscous resistivity.

Subject

Aerodynamic noise
Beamforming
Boundary layer
Geometric modelling
Sound absorbing materials

To reference this document use:

http://resolver.tudelft.nl/uuid:917dcadd-4e45-4a3a-b671-74444a51153d

DOI

https://doi.org/10.1016/j.apacoust.2022.108989

ISSN

0003-682X

Source

Applied Acoustics, 199

Part of collection

Institutional Repository