Inflow broadband noise from an isolated symmetric airfoil interacting with incident turbulence

Kim, Dae-Hwan; Lee, Gwang-Se; Cheong, Cheolung

doi:10.1016/j.jfluidstructs.2015.03.015

Cited by 30 publications

(15 citation statements)

References 36 publications

(79 reference statements)

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“…Although twodimensional turbulence was used in a number of works, 6,24 it cannot be employed to reproduce experimental results without applying some correction factors.…”

Section: Two-dimensional Advanced Digital Filter Methodsmentioning

confidence: 99%

Synthetic Turbulence Methods for Leading Edge Noise Predictions

Gea-Aguilera

Zhang

Chen

et al. 2015

21st AIAA/CEAS Aeroacoustics Conference

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An advanced digital filter method to generate synthetic turbulence is presented for efficient two-and three-dimensional leading edge noise predictions. The technique, which is based on the Random Particle-Mesh method, produces a turbulent inflow that matches a target isotropic energy spectrum. The discretized equations for the synthetic eddies, and the input parameters needed to recover the desired turbulence statistics, are presented. Moreover, a simple and fast implementation strategy, which does not require an additional boundary condition, is presented under the frozen turbulence assumption. The method is used in a linearized Euler solver to predict turbulence-airfoil interaction noise from a number of configurations, including variations in airfoil thickness, angle of attack and Mach number. For the first time, noise predictions from a digital filter method are directly compared to those provided by synthetic turbulence based on a summation of Fourier modes. The comparison indicates that the advanced digital filter method gives enhanced performance in terms of computational cost and simulation accuracy. In addition, initial tests show that this method is capable of reproducing experimental noise measurements within 3 dB accuracy.

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“…Although twodimensional turbulence was used in a number of works, 6,24 it cannot be employed to reproduce experimental results without applying some correction factors.…”

Section: Two-dimensional Advanced Digital Filter Methodsmentioning

confidence: 99%

Synthetic Turbulence Methods for Leading Edge Noise Predictions

Gea-Aguilera

Zhang

Chen

et al. 2015

21st AIAA/CEAS Aeroacoustics Conference

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“…The distortion of the turbulent structures in the leading edge region is believed to be responsible for the noise reduction of thick airfoils at high frequencies. Previous works examined the distortion of harmonic gusts 32,35 and isotropic turbulence 23,34 in two-dimensional CAA simulations of isolated airfoils. Additionally, experiments of airfoils with straight leading edge have also been performed to study the turbulent flow features in the leading edge region.…”

Section: Via Distortion Of Turbulent Structures and Velocity Spectramentioning

confidence: 99%

Wavy Leading Edge Airfoils Interacting with Anisotropic Turbulence

Aguilera

Gill

Angland

et al. 2017

23rd AIAA/CEAS Aeroacoustics Conference

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Leading edge noise reductions caused by serrations have been shown to be sensitive to the length scales of vortical disturbances. In order to improve the understanding of wavy leading edge airfoils as a noise reduction technology, this paper examines the effects of anisotropy on turbulence-airfoil interaction noise by means of computational aeroacoutic simulations. A synthetic turbulence method is used to generate fully three-dimensional, divergence-free, homogeneous anisotropic turbulence, which is injected in a linearized Euler equation solver to model the noise generation. Moderate variations in turbulence length scales, which are representative of the anisotropy in aero-engine fan wakes, are tested for a NACA 0012 airfoil with a wavy leading edge. This work focuses on the noise sources in the near-field by examining the distortion of the turbulent structures and velocity spectra in the vicinity of the noise sources, the unsteady pressure and its spectral density on the airfoil surface, the magnitude-squared coherence between velocity and pressure fluctuations on the noise sources, and the correlation between noise sources along the span for various degrees of anisotropy. Numerical results show that small variations in the turbulence length scales can produce significant changes in the spectral content of the noise sources at the peak and root regions. The loudest noise source is always located in the root region for the cases examined and this source is mainly affected by the transverse velocity fluctuations. To reduce the correlation between noise sources in the peak and root regions, the ratio between the chordwise length scale and the amplitude of the serrations, and the ratio between the spanwise length scale and the wavelength of the leading edge should satisfy lx/(2hw) < 1 and lz/λw ≤ 0.5, respectively.Recent experimental, numerical, and analytical studies 6,8,14,15 highlighted the importance of the length scales of the vortical disturbances or turbulence as a key parameter in the noise reduction of wavy leading edge airfoils. However, the majority of previous works were based on the flat plate assumption 8, 16 and used simplified representations for the turbulence, such as harmonic gusts 14 or isotropic turbulence. 8 Unlike previous works that focused on flat plates and isotropic turbulence, the present work studies the noise generation mechanisms of an airfoil with wavy leading edge in the presence of anisotropic turbulence. Although the effects of anisotropic turbulence have been shown to be limited in airfoils with straight leading edge, 17 wavy leading edge airfoils are expected to be more sensitive to anisotropic turbulence due to additional three-dimensional mechanisms caused by the amplitude and wavelength of the leading edge serrations. In this work, Computational AeroAcoustic (CAA) simulations are performed by means of a synthetic turbulence method to generate fully three-dimensional anisotropic turbulence and a linearized Euler equation (LEE) solver for the noise generation. The following top...

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“…angle of attack, aerofoil thickness, camber, etc.) on ATI noise have been studied in [4][5][6][7][8][9][10][11][12] predominantly in two-dimensional space and/or sinusoidal gust functions.…”

Section: Introductionmentioning

confidence: 99%

On the mechanisms of noise reduction in aerofoil-turbulence interaction by using wavy leading edges

Haeri

Kim

Joseph

2015

21st AIAA/CEAS Aeroacoustics Conference

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A novel aerofoil leading-edge profile based on wavy (sinusoidal) protuberances/tubercles is investigated numerically to understand its effectiveness for the reduction of aerofoilturbulence interaction noise. Non-lifting flat-plate aerofoils with straight and wavy leading edges (denoted by SLE and WLE, respectively) are employed and subjected to an impinging turbulence that is synthetically generated in the upstream zone. A full three-dimensional Euler (inviscid) simulations are performed for this study in order to avoid developing selfnoise due to viscosity. The free-stream Mach number is set to 0.24. A high-order accurate finite-difference based solver and artefact-free boundary conditions are used in the current simulations. Various frequency-spectra and statistical analysis are implemented in order to investigate and understand the noise reduction mechanisms.

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Inflow broadband noise from an isolated symmetric airfoil interacting with incident turbulence

Cited by 30 publications

References 36 publications

Synthetic Turbulence Methods for Leading Edge Noise Predictions

Synthetic Turbulence Methods for Leading Edge Noise Predictions

Wavy Leading Edge Airfoils Interacting with Anisotropic Turbulence

On the mechanisms of noise reduction in aerofoil-turbulence interaction by using wavy leading edges

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