Aeroacoustic Characteristics of a NACA 0012 Airfoil for Attached and Stalled Flow Conditions

Mayer, Yannick D; Zang, Bin; Azarpeyvand, Mahdi

doi:10.2514/6.2019-2530

Cited by 25 publications

(24 citation statements)

References 24 publications

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“…This resulted in an unreasonably large prediction for the final 30% of the chord, which indicated that the radiated noise may be generated further upstream from the TE. Similarly, Mayer et al [9] have demonstrated an increase in low frequency energy and coherence along the full aerofoil chord as the angle of attack is increased into the stall regime.…”

Section: Introductionmentioning

confidence: 72%

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Aerofoil dipole noise due to flow separation and stall at a low Reynolds number

Turner

Kim

2020

International Journal of Heat and Fluid Flow

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Aerofoil self-noise produced by flow separation and stall is relatively little understood regarding the underlying generation mechanisms. The focus of this work is to provide an improved level of understanding particularly with regard to the dipole noise sources utilising a high-fidelity direct numerical simulation. A NACA0012 aerofoil is considered under three different flow conditions at a Reynolds number Re ∞ = 50, 000 and a Mach number M ∞ = 0.4. These include: a pre-stall condition with a laminar separation bubble (α = 5 •), near-stall (α = 10 •), and fully stalled (α = 15 •). The noise radiation in the far-field is significantly increased at low frequencies for the full-stall case for all observer directions which is consistent with previous experimental observations. The dominant source regions for each configuration are identified for low, medium and high frequencies, separately. A number of key findings are made concerning the source characteristics in full-stall case which differ considerably from the lower angle of attack cases. It is found that the location of the dominant sources changes more significantly with frequency for the full-stall case. Additionally, for medium to high frequencies the maximum acoustic source amplitude is weaker for the full-stall case, despite comparable levels observed in the far-field. This seemingly contradictory observation highlights the importance of phase variations in the wall pressure fluctuations. For the frequencies considered in this paper it is shown that the full-stall case usually produces a relatively more in-phase source distribution, resulting in a more efficient radiation despite the lower amplitude levels. The important flow structures which are responsible for the dipole sources are also identified through analysis of the pressure field at isolated frequencies. It is found that for low frequencies coherent structures in the shear layer are responsible for the scattering of the wall pressure fluctuations at the TE, which agrees with previous findings in the literature. However, at medium and high frequencies the shear layer structures are found to be relatively weak in the proximity of the TE. This indicates that the noise may be generated through other means, for example scattering of fluctuating pressure induced by vortices shed from the TE.

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Section: Introductionmentioning

confidence: 72%

“…The most prominent observation in the literature is that the stall is characterised by a high level of low frequency sound [2][3][4][5][6][7][8][9]. More specifically, in the light stall regime increased low frequency broadband levels are observed, while in deep stall low frequency tones are also exhibited [5].…”

Section: Introductionmentioning

confidence: 99%

Aerofoil dipole noise due to flow separation and stall at a low Reynolds number

Turner

Kim

2020

International Journal of Heat and Fluid Flow

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“…To determine the lateral correlation length of turbulence structures, an array of seven microphones, distributed along the airfoil span at 0.99c, was used. A full description of the airfoil and its instrumentation can be found in [35] and [36].…”

Section: B Airfoil and Instrumentationmentioning

confidence: 99%

Application of Finlets for Trailing Edge Noise Reduction of a NACA 0012 Airfoil

Gstrein¹,

Zang²,

Azarpeyvand³

2020

Aiaa Aviation 2020 Forum

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The present experiments investigate the reduction of trailing edge noise of a symmetric NACA 0012 airfoil using surface treatments, known as finlets. Treatment effectiveness is measured with observations from far-field data. Moreover, the highly instrumented airfoil model allows measurements of both static and dynamic surface pressure at various chord-and spanwise locations. In particular, measurements were carried out in between of the finlets, in order to elucidate clearly the near-field dynamics. With this, key parameters associated with trailing edge noise reduction could be identified. Relevant factors are, for instance, the spacing and the height of the finlets, as well as their relative positions with reference to the trailing edge. The results suggest that there possibly exists a strong correlation between the finlet height and the boundary layer thickness at the trailing edge. Attempting to identify different noise reduction mechanisms described in the previous studies, it was concluded that the prevailing one for airfoils is likely to be the detachment of small-scale turbulence structures from the airfoil surface. From the results of a position study it was inferred that shifting a treatment upstream from the airfoil trailing edge leads to beneficial effects in terms of trailing edge noise reduction compared to the configuration with the treatment applied flush with the trailing edge.

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“…In what follows, we will explain each setup and provide the far-field noise data to show the performance of the new facility. Further experimental results for airfoils, high-lift devices and bluff bodies can be found elsewhere[36][37][38][39][40].…”

mentioning

confidence: 99%

Design and performance of an aeroacoustic wind tunnel facility at the University of Bristol

Mayer¹,

Jawahar²,

Szoke

et al. 2019

Applied Acoustics

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107

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This paper provides an overview of the design and performance of the new aeroacoustic wind tunnel facility at the University of Bristol. The purpose of the facility is to enable near-and far-field acoustic and aerodynamic studies on a variety of different aerodynamic components and to examine diverse noise control techniques. The facility comprises a large acoustic chamber, anechoic down to 160 Hz, and a temperature controlled closed-circuit wind tunnel with an open test section. The wind tunnel features two interchangeable rectangular nozzles with a partially shared contraction. Both nozzles are shown to possess a high flow quality with high flow uniformity and low turbulence intensity of 0.09% and 0.12% for the smaller and larger nozzle, respectively. The maximum attainable flow speeds are 40 m/s for the larger nozzle and 120 m/s for the smaller nozzle corresponding to Reynolds numbers of 2.7 million and 8.1 million per meter, respectively. In this paper, we will present various aerodynamic and acoustic results to characterize the performance of the facility. The background noise levels are found to be sufficiently low and the far-field noise measurements from a flat plate, a round cylinder and a NACA 0012 airfoil compare favorably to existing experimental observations.

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Aeroacoustic Characteristics of a NACA 0012 Airfoil for Attached and Stalled Flow Conditions

Cited by 25 publications

References 24 publications

Aerofoil dipole noise due to flow separation and stall at a low Reynolds number

Aerofoil dipole noise due to flow separation and stall at a low Reynolds number

Application of Finlets for Trailing Edge Noise Reduction of a NACA 0012 Airfoil

Design and performance of an aeroacoustic wind tunnel facility at the University of Bristol

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