Quadrupole noise generated from a low-speed aerofoil in near- and full-stall conditions
Quadrupole noise generated from a low-speed aerofoil in near- and full-stall conditions
In this paper, direct numerical simulations are performed for low-speed flows past a NACA0012 aerofoil at high incidence angles. The aim is to investigate the significance of quadrupole noise generated due to separated shear layers, in comparison to dipole noise emanating from the aerofoil surface. The two different noise components (dipole and quadrupole) are calculated by using the Ffowcs Williams & Hawkings method in two different approaches: One with a solid surface and another with a permeable surface. The quadrupole noise is then estimated approximately by taking the relative difference between the two. The current study provides detailed comparisons between the quadrupole and dipole noise components at various observer locations in a wide range of frequencies. The comparisons are also made in terms of Mach number scaling, which differs significantly from theoretical predictions and changes rapidly with frequency. Additionally, pre-, near- A nd full-stall conditions are cross-examined, which reveals significant differences in the quadrupole contributions, including changes in the major source locations and frequencies. It is found that the inclusion of the quadrupole sources gives rise to the predicted noise power level at all frequencies (varying between 2 and 10 dB for an observer above the aerofoil) compared to the dipole-only case. The quadrupole contribution is far from negligible even at the low subsonic speeds (Mach 0.3 and 0.4) when aerofoil stall occurs.
aeroacoustics, separated flows
Turner, Jacob
8618df92-3b0c-46e6-a482-dd12b261d9a7
Kim, Jae Wook
fedabfc6-312c-40fd-b0c1-7b4a3ca80987
15 February 2022
Turner, Jacob
8618df92-3b0c-46e6-a482-dd12b261d9a7
Kim, Jae Wook
fedabfc6-312c-40fd-b0c1-7b4a3ca80987
Turner, Jacob and Kim, Jae Wook
(2022)
Quadrupole noise generated from a low-speed aerofoil in near- and full-stall conditions.
Journal of Fluid Mechanics, 936, [A34].
(doi:10.1017/jfm.2022.75).
Abstract
In this paper, direct numerical simulations are performed for low-speed flows past a NACA0012 aerofoil at high incidence angles. The aim is to investigate the significance of quadrupole noise generated due to separated shear layers, in comparison to dipole noise emanating from the aerofoil surface. The two different noise components (dipole and quadrupole) are calculated by using the Ffowcs Williams & Hawkings method in two different approaches: One with a solid surface and another with a permeable surface. The quadrupole noise is then estimated approximately by taking the relative difference between the two. The current study provides detailed comparisons between the quadrupole and dipole noise components at various observer locations in a wide range of frequencies. The comparisons are also made in terms of Mach number scaling, which differs significantly from theoretical predictions and changes rapidly with frequency. Additionally, pre-, near- A nd full-stall conditions are cross-examined, which reveals significant differences in the quadrupole contributions, including changes in the major source locations and frequencies. It is found that the inclusion of the quadrupole sources gives rise to the predicted noise power level at all frequencies (varying between 2 and 10 dB for an observer above the aerofoil) compared to the dipole-only case. The quadrupole contribution is far from negligible even at the low subsonic speeds (Mach 0.3 and 0.4) when aerofoil stall occurs.
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Submitted date: 2 May 2021
Accepted/In Press date: 9 January 2022
Published date: 15 February 2022
Additional Information:
Funding Information:
We would like to thank EPSRC (Engineering and Physical Sciences Research Council) for the computational time made available on the UK supercomputing facility ARCHER via grants EP/R010900/1 and the UK Turbulence Consortium (EP/R029326/1). We also acknowledge the high-performance computing facilities and services offered by the local IRIDIS5 at the University of Southampton. All data supporting this study are openly available from the University of Southampton repository at http://dx.doi.org/10.5258/SOTON/D2095 .
Funding Information:
The authors gratefully acknowledge the support of the ESPRC (Engineering and Physical Sciences Research Council) under grant EP/R010900/1.
Publisher Copyright:
© 2022 The Author(s). Published by Cambridge University Press.
Keywords:
aeroacoustics, separated flows
Identifiers
Local EPrints ID: 448943
URI: http://eprints.soton.ac.uk/id/eprint/448943
ISSN: 0022-1120
PURE UUID: 7f46583e-88ee-4904-b242-72d2dd0df19e
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Date deposited: 11 May 2021 17:10
Last modified: 17 Mar 2024 06:32
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Jacob Turner
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