Jet-installation noise reduction with flow-permeable materials

Journal article (2021)

Authors

Leandro Rego Wind Energy - Aerospace Engineering
D. Ragni Wind Energy - Aerospace Engineering
F. Avallone Wind Energy - Aerospace Engineering
D. Casalino Wind Energy - Aerospace Engineering
R. Zamponi Wind Energy - Aerospace Engineering , von Karman Institute for Fluid Dynamics, Novel Aerospace Materials - Aerospace Engineering
C Schram von Karman Institute for Fluid Dynamics
Research Group
Wind Energy (Aerospace Engineering) (TU Delft)
Copyright: © 2021 Leandro Rego, D. Ragni, F. Avallone, D. Casalino, R. Zamponi, Christophe Schram
DOI: https://doi.org/10.1016/j.jsv.2021.115959
More Info
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Published Date

2021

Language

English

Faculty

Aerospace Engineering

Department

Flow Physics and Technology

Research Group

Wind Energy

Abstract

This paper investigates the application of flow-permeable materials as a solution for reducing jet-installation noise. Experiments are carried out with a flat plate placed in the near field of a single-stream subsonic jet. The flat plate is modular and the solid surface near the trailing edge can be replaced with different flow-permeable inserts, such as a metal foam and a perforated plate structure. The time-averaged jet flow field is characterized through planar PIV measurements at three different velocities (Ma=0.3, Ma=0.5 and Ma=0.8, where Ma is the acoustic Mach number), whereas the acoustic far-field is measured with a microphone arc-array. Acoustic measurements confirm that installation effects cause significant noise increase, up to 17 dB for the lowest jet velocity, particularly at low and mid frequencies (i.e. St<0.7, with the Strouhal number based on the jet diameter and velocity), and mostly in the upstream direction of the jet. By replacing the solid trailing edge with the metal foam, noise abatement of up to 9 dB is achieved at the spectral peak for Ma=0.3 and a polar angle θ=40∘, with an overall reduction in the entire frequency range where jet-installation noise is dominant. The perforated plate provides lower noise reduction than the metal foam (7 dB at the spectral peak for Ma=0.3 and θ=40∘), and it is less effective at low frequencies. This is related to the values of permeability and form coefficient of the materials, which are the major parameters controlling the pressure balance across the trailing edge and, consequently, the noise generated by the plate. However, despite having a high permeability, the plate with the metal-foam trailing edge still has a distinct noise production at mid frequencies (St≈0.43 for Ma=0.3). Based on the analyses of different treated surface lengths, it is conjectured that the solid-permeable junction in the plate acts as a new scattering region, and thus its position also affects the far-field noise, which is in line with analytical predictions in the literature. Nonetheless, both types of inserts provide significant noise reduction and are potential solutions for the problem of jet-installation noise.