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Manipulation of mid- and high-frequency wall-pressure sources by streamwise finlets

Published online by Cambridge University Press:  21 February 2025

Zhihang Pan  and
Qingqing Ye Open the ORCID record for Qingqing Ye [Opens in a new window]
Zhihang Pan
Affiliation:
State Key Laboratory of Fluid Power and Mechatronic Systems, Department of Mechanics, Zhejiang University, Hangzhou 310027, PR China
Qingqing Ye*
Affiliation:
State Key Laboratory of Fluid Power and Mechatronic Systems, Department of Mechanics, Zhejiang University, Hangzhou 310027, PR China
*
†Email address for correspondence: [email protected]
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Abstract

In the present research, the effect of streamwise finlets on the coherent structures of a turbulent boundary layer and their relation with pressure fluctuations and trailing-edge noise is investigated experimentally over a NACA0018 airfoil. A synthetic measurement is performed using time-resolved particle image velocimetry, wall-pressure transducers and a far-field microphone. The finlets induce strong momentum transport within the boundary layer, leading to the formation of a detached shear layer and backward flow separation. A strong velocity deficit is produced close to the wall. The instantaneous flow organisation reveals the formation of hairpin-like vortices on top of the finlets and spanwise rollers in the near-wall separation bubble. The newly generated vortices disrupt the turbulent coherent structures of the untreated case remarkably. An overall lift-up process of the unsteady turbulent structures is produced, bringing the most energetic turbulent structures away from the wall and reducing the near-wall shear stress. The spatial and temporal relation between instantaneous unsteady flow features and wall-pressure fluctuations is analysed quantitatively. A notable reduction of the correlation and coherence intensity in the mid- and high-frequency bands is achieved due to the modification of the turbulent structures. The former frequency ranges agree with that of the pressure fluctuations and far-field noise suppression, revealing the noise-reduction mechanisms.

JFM classification

Acoustics: Aeroacoustics Boundary Layers: Boundary layer structure Boundary Layers: Boundary layer control
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 1005 , 25 February 2025 , A8
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Copyright
© The Author(s), 2025. Published by Cambridge University Press

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Supplementary material: File

Pan and Ye supplementary movie 1

Normalized instantaneous streamwise velocity (u/U∞) for the untreated case.
Download Pan and Ye supplementary movie 1(File)
File 7.8 MB
Supplementary material: File

Pan and Ye supplementary movie 2

Normalized instantaneous streamwise velocity fluctuations (u′/U∞) for the untreated case.
Download Pan and Ye supplementary movie 2(File)
File 7 MB
Supplementary material: File

Pan and Ye supplementary movie 3

Normalized instantaneous streamwise velocity (u/U∞) for the S3-F case.
Download Pan and Ye supplementary movie 3(File)
File 7.3 MB
Supplementary material: File

Pan and Ye supplementary movie 4

Normalized instantaneous streamwise velocity fluctuations (u′/U∞) for the S3-F case.
Download Pan and Ye supplementary movie 4(File)
File 6.8 MB
Supplementary material: File

Pan and Ye supplementary movie 5

Normalized instantaneous streamwise velocity (u/U∞) for the S3-M case.
Download Pan and Ye supplementary movie 5(File)
File 7.9 MB
Supplementary material: File

Pan and Ye supplementary movie 6

Normalized instantaneous streamwise velocity fluctuations (u′/U∞) for the S3-M case.
Download Pan and Ye supplementary movie 6(File)
File 6.6 MB