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

Nguyen, Lap; Golubev, Vladimir V.; Mankbadi, Reda R.; Yakhina, Gyuzel; Roger, Michel

doi:10.3390/app11052257

Cited by 13 publications

(15 citation statements)

References 33 publications

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“…Tonal noise emission has been extensively reported for flow conditions with the chord-based Reynolds number 5 × 10 4 < Re < 2 × 10 6 and the angle of attack |α| < 10 • on symmetric aerofoils, e.g. NACA 0006, NACA 0008 (Sandberg et al 2009), NACA 0012 (Paterson et al 1973;Desquesnes et al 2007;Jones & Sandberg 2011;Stalnov, Chaitanya & Joseph 2016;Golubev 2021;Nguyen et al 2021) and NACA 0018 (Paterson et al 1973;Nakano, Fujisawa & Lee 2006). Cambered aerofoils designed for small wind turbines and fan blades were also reported to generate tonal noise in the Reynolds number range of 5 × 10 4 -6 × 10 5 and light loading conditions (Longhouse 1977;Oerlemans 2003;Wang et al 2009;Sanjose et al 2019;Yakhina et al 2020).…”

Section: Introductionmentioning

confidence: 99%

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A secondary modulation mechanism for aerofoil tonal self-noise generation

Yang

Pröbsting

et al. 2022

J. Fluid Mech.

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Acoustic emission of a NACA 0012 aerofoil is investigated over a range of free-stream velocities. Acoustic spectra show a dominant tone and two sets of weaker side tones characterised by different frequency intervals. The frequency of the dominant tones in the acoustic spectra varies with velocity in a ladder-type structure. With increasing Reynolds number, the spectrum becomes progressively more broadband in nature. Through synchronised particle image velocimetry and acoustic measurements, the aeroacoustic noise generation mechanisms, resulting in different spectral characteristics and modulation types, are further investigated. A separation bubble and related significant velocity fluctuations are observed on the pressure side. Pressure side velocity spectra show characteristics similar to the acoustic ones, whereas velocity spectra on the suction side feature broadband characteristics. These findings confirm that noise emission is dominated by pressure side events for the Reynolds number range of this study, i.e. $2 \times 10^{5}$ – $7 \times 10^{5}$ . As the acoustic emission is defined by coherent flow structures, the proper orthogonal decomposition method is adopted to facilitate the understanding of the relation between the complex flow field and acoustic emission. Side tones in the acoustic spectra are attributed to two different modulation mechanisms in the aeroacoustic source region near the trailing edge. By aligning the sound pressure time history and the time coefficients of the dominant modes, the primary modulation of the dominant tone is found to be related to the amplitude modulation of the high-frequency velocity fluctuations associated with the acoustic feedback loop. A secondary modulation is attributed to periodic variation of the separation bubble and, therefore, variation in the roll-up of the shear layer, which results in a modulation of the amplitude of the velocity fluctuations associated with the convecting vortices at the trailing edge.

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Section: Introductionmentioning

confidence: 99%

“…2015; Stalnov, Chaitanya & Joseph 2016; Golubev 2021; Nguyen et al. 2021) and NACA 0018 (Paterson et al. 1973; Nakano, Fujisawa & Lee 2006).…”

Section: Introductionmentioning

confidence: 99%

A secondary modulation mechanism for aerofoil tonal self-noise generation

Yang

Pröbsting

et al. 2022

J. Fluid Mech.

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“…These simulations provided valuable insights on the noise sources but could not account for intrinsic threedimensional (3D) effects, such as vortex stretching and transition to turbulence. To over-come this limitation, 3D simulations have been recently employed to investigate such effects in the context of airfoil secondary tones and the feedback loop mechanisms [9,10,[12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Switch of tonal noise generation mechanisms in airfoil transitional flows

Ricciardi,

Wolf

2022

Preprint

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Large eddy simulations are performed to study tonal noise generation by a NACA0012 airfoil at an angle of attack α = 3 deg. and freestream Mach number of M ∞ = 0.3. Different Reynolds numbers are analyzed spanning 0.5 × 10 5 ≤ Re ≤ 4 × 10 5 . Results show that the flow patterns responsible for noise generation appear from different laminar separation bubbles, including one observed over the airfoil suction side and another near the trailing edge, on the pressure side. For lower Reynolds numbers, intermittent vortex dynamics on the suction side results in either coherent structures or turbulent packets advected towards the trailing edge. Such flow dynamics also affects the separation bubbles on the pressure side, which become intermittent. Despite the irregular occurrence of laminar-turbulent transition, the noise spectrum depicts a main tone with multiple equidistant secondary tones. Increasing the Reynolds number leads to a permanent turbulent regime on the suction side that reduces the coherence level causing only small scale turbulent eddies to be observed. Furthermore, the laminar separation bubble on the suction side almost vanishes while that on the pressure side becomes more pronounced and permanent. As a consequence, the dominant noise generation mechanism becomes the vortex shedding along the wake.

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“…Other TE noise sources exist, such as the vortex shedding entailed by a blunted trailing edge (which also generates a strong tonal, dipolar acoustic emission), or the flow separation occurring in the early stage of stall (as opposed to the deep stall one, which rather results in noise radiating from the entire airfoil). Given its multiple components and complex physics, the airfoil trailing edge (TE) noise is still only partly understood [1][2][3], despite half a century of investigations using either experimental [1,[4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], theoretical [15][16][17][18][19], or computational [20][21][22][23][24][25] means.…”

Section: Introductionmentioning

confidence: 99%

“…Last but not least, open jets are likely to alter the far-field noise radiation, due to both acoustic refraction (by the jet shear layers [28]) and acoustic diffusion (by the jet fine scale turbulence). Although these effects can be corrected a posteriori through analytical and/or semi-empirical means [29][30][31][32][33], such corrections imply some restrictive assumptions that make them partly conclusive only [25] (e.g., the plug flow model by Amiet [29,30]).…”

Section: Introductionmentioning

confidence: 99%

Theoretical Study of the Acoustic Installation Effects in Closed-Vein Wind Tunnels for the Experimental Characterization of Trailing Edge Noise

Redonnet

2021

Applied Sciences

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This study focuses on the acoustic installation effects that may occur during typical aeroacoustic experiments when the latter are conducted in a closed-vein wind tunnel. More precisely, in regard to the specific problem of airfoil trailing edge noise, an analytical model is derived, which allows predicting the wall-induced reverberation effects that such a noise shall be subjected to, when radiating within a closed-vein, hard-wall, wind tunnel. These effects are then assessed through a parametric investigation so as to characterize their impact on in situ acoustic measurements that would be performed using flush-mounted microphones located on the vein’s walls. From a phenomenological perspective, the study highlights how important the reverberation effects by the vein can be. In particular, results reveal how their impact on the noise measurements may greatly vary, depending on the trailing edge noise source location (i.e., the airfoil incidence) and, to a lesser extent, its frequency. The outcomes allow identifying these locations where the installation effects are least, i.e., where to better position a flush-mounted microphone, should in situ noise measurements be conducted. From a methodological viewpoint, the study showcases how the proposed formalism could constitute a simple albeit useful diagnosis tool for mitigating the experimental biases weighing on airfoil trailing edge noise tests to be conducted within closed-vein facilities, whether this would be done a priori by flush-mounting the microphone(s) where these biases are minimal or a posteriori by de-biasing the noise measurements accordingly.

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

Cited by 13 publications

References 33 publications

A secondary modulation mechanism for aerofoil tonal self-noise generation

A secondary modulation mechanism for aerofoil tonal self-noise generation

Switch of tonal noise generation mechanisms in airfoil transitional flows

Theoretical Study of the Acoustic Installation Effects in Closed-Vein Wind Tunnels for the Experimental Characterization of Trailing Edge Noise

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