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SPOD analysis of noise-generating Rossiter modes in a slat with and without a bulb seal

Published online by Cambridge University Press:  18 March 2021

Fernando H.T. Himeno Open the ORCID record for Fernando H.T. Himeno [Opens in a new window] ,
Daniel S. Souza Open the ORCID record for Daniel S. Souza [Opens in a new window] ,
Filipe R. Amaral Open the ORCID record for Filipe R. Amaral [Opens in a new window] ,
Daniel Rodríguez Open the ORCID record for Daniel Rodríguez [Opens in a new window]  and
Marcello A.F. Medeiros Open the ORCID record for Marcello A.F. Medeiros [Opens in a new window]
Fernando H.T. Himeno*
Affiliation:
Department of Aeronautical Engineering, University of São Paulo, Av. Trabalhador São Carlense, 400, São Carlos, SP 13566-590, Brazil
Daniel S. Souza
Affiliation:
UNESP – São Paulo State University, Av. Profa. Isette Correa Fontão 505, São João da Boa Vista, São Paulo, 13876-750, Brazil
Filipe R. Amaral
Affiliation:
Department of Aeronautical Engineering, University of São Paulo, Av. Trabalhador São Carlense, 400, São Carlos, SP 13566-590, Brazil Aeronautics Institute of Technology, Praça Marechal Eduardo Gomes 50, São José dos Campos, São Paulo, 12228-900, Brazil
Daniel Rodríguez
Affiliation:
ETSIAE-UPM (School of Aeronautics), Universidad Politécnica de Madrid, Plaza del Cardenal Cisneros 3, 28040Madrid, Spain
Marcello A.F. Medeiros
Affiliation:
Department of Aeronautical Engineering, University of São Paulo, Av. Trabalhador São Carlense, 400, São Carlos, SP 13566-590, Brazil
*
†Email address for correspondence: fernando.himeno@usp.br
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Abstract

The slat represents an important airframe noise source as it extends over almost the entire aircraft wingspan. Most studies of slat noise consider idealized geometries. However, for practical applications, several elements are installed on its cove, such as bulb seals to avoid direct contact with the main wing surface. Previous investigations of an unswept and untapered MD30P30N airfoil reported that the flow dynamics and the corresponding acoustic noise are very sensitive to the presence and location of the bulb seal. For certain locations a second recirculation bubble is created inside the slat cove and the acoustic narrowband peaks are intensified. The present paper shows that the two-bubble topology promotes the recirculation of turbulence within the slat cove. Spectral proper orthogonal decomposition analysis based on the radiated pressure intensity is used to identify the flow structures responsible for sound generation. Even though the recirculating turbulence is mostly incoherent, it interacts with the coherent Kelvin–Helmholtz vortices in the initial part of the mixing layer. Then, vortex merging and straining lead to the formation of complex vortex clusters. Our results show that the origin and evolution of these clusters are consistent with Rossiter's mechanism responsible for the narrowband peaks. The enhanced recirculation accelerates the cluster evolution leading to wider clusters and lower-frequency Rossiter modes.

JFM classification

Acoustics: Aeroacoustics Nonlinear Dynamical Systems: Low-dimensional models Vortex Flows: Vortex interactions
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 915 , 25 May 2021 , A67
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Copyright
© The Author(s), 2021. Published by Cambridge University Press

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References

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