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Recent Advances in Acoustics of Transitional Airfoils with Feedback-Loop Interactions: A Review
Article

Numerical Investigation of Tonal Trailing-Edge Noise Radiated by Low Reynolds Number Airfoils

1
Department of Aerospace Engineering, Embry-Riddle Aeronautical University, Daytona Beach, FL 32114, USA
2
Laboratoire de Mecanique des Fluides et Acoustique, Ecole Centrale de Lyon, 69134 Ecully, France
*
Authors to whom correspondence should be addressed.
Academic Editor: Roberto Camussi
Appl. Sci. 2021, 11(5), 2257; https://doi.org/10.3390/app11052257
Received: 31 December 2020 / Revised: 30 January 2021 / Accepted: 27 February 2021 / Published: 4 March 2021
(This article belongs to the Special Issue Airframe Noise and Airframe/Propulsion Integration)
A high-fidelity computational analysis carefully validated against concurrently obtained experimental results is employed to examine self-noise radiation of airfoils at transitional flow regimes, with a focus on elucidating the connection between the unsteady behavior of the laminar separation bubble (LSB) and the acoustic feedback-loop (AFL) resonant interactions observed in the airfoil boundary layers. The employed parametric study examines AFL sensitivity to the changes in the upstream flow conditions and the airfoil loading. Implicit Large-Eddy Simulations are performed for a NACA-0012 airfoil in selected transitional-flow regimes for which experimental measurements recorded characteristic multiple-tone acoustic spectra with a dual ladder-type frequency structure. The switch between the tone-producing and no-tone-producing regimes is traced to the LSB size and position as a function of the flow Reynolds number and the airfoil angle of attack, and further substantiated by the linear stability analysis. The results indicate a strong multi-tonal airfoil noise radiation associated with the AFL and attributed to the switch from the slowly-growing Tollmien–Schlichting to the fast-growing Kelvin–Helmholtz instabilities occurring in thin LSB regions when those are localized near the trailing-edge (TE) on either side of the airfoil. Such a process eventually results in the nonlinearly saturated flapping vortical modes (“rollers”) that scatter into acoustic waves at the TE. View Full-Text
Keywords: airfoil trailing-edge (TE) noise; Implicit Large-Eddy Simulations (ILES); acoustic feedback loop (AFL); boundary-layer (BL); Tollmien–Schlichting (T-S); Kelvin–Helmholtz (K-H) instabilities airfoil trailing-edge (TE) noise; Implicit Large-Eddy Simulations (ILES); acoustic feedback loop (AFL); boundary-layer (BL); Tollmien–Schlichting (T-S); Kelvin–Helmholtz (K-H) instabilities
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MDPI and ACS Style

Nguyen, L.; Golubev, V.; Mankbadi, R.; Yakhina, G.; Roger, M. Numerical Investigation of Tonal Trailing-Edge Noise Radiated by Low Reynolds Number Airfoils. Appl. Sci. 2021, 11, 2257. https://doi.org/10.3390/app11052257

AMA Style

Nguyen L, Golubev V, Mankbadi R, Yakhina G, Roger M. Numerical Investigation of Tonal Trailing-Edge Noise Radiated by Low Reynolds Number Airfoils. Applied Sciences. 2021; 11(5):2257. https://doi.org/10.3390/app11052257

Chicago/Turabian Style

Nguyen, Lap, Vladimir Golubev, Reda Mankbadi, Gyuzel Yakhina, and Michel Roger. 2021. "Numerical Investigation of Tonal Trailing-Edge Noise Radiated by Low Reynolds Number Airfoils" Applied Sciences 11, no. 5: 2257. https://doi.org/10.3390/app11052257

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