Noise generated by airfoil profiles placed in a uniform laminar flow

Arbey, H.; Bataille, J.

doi:10.1017/s0022112083003201

Cited by 276 publications

(262 citation statements)

References 13 publications

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“…In this velocity range the spectrum is characterized by numerous and equally-spaced discrete frequencies (sometimes as many as 10 at a single velocity). Identical behaviour is found in the experimental and numerical works of [2,3,5,7,23]. For the S1, S2 and S3 serrations, there is no sudden jump in OASPL at 20 ms -1 < v j < 60 ms -1 and it is found that OASPL (S1, S2, and S3)  v j…”

Section: 4supporting

confidence: 69%

“…1). Based solely on Model A, the tonal frequencies can be predicted [2,3,5] from the frequencies, f n , at which the phase change around the loop 2F(f n ), given by…”

Section: Assessment Of Feedback Mechanism Based On Model Amentioning

confidence: 99%

“…Trailing edge noise radiated in high Reynolds number flow ( > 10 6 ), for example, is typically broadband in nature. By contrast, for low Reynolds number with minimal residue turbulence in the freestream, trailing edge noise has a distinctive narrowband character comprising a broadband hump superimposed with a number of high amplitude "tones" [2,3]. In this situation the boundary layer on the airfoil surface is mainly laminar but potentially unstable.…”

Section: Introductionmentioning

confidence: 98%

“…1. Model A [2,5] assumes that acoustic waves generated at the trailing edge will radiate upstream to disturb the boundary layer from which the T-S wave originated. Subsequently the T-S waves propagate to the trailing edge and radiate the broadband hump, and so on.…”

Section: Introductionmentioning

confidence: 99%

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An experimental study of airfoil instability tonal noise with trailing edge serrations

Chong¹,

Joseph²

2013

Journal of Sound and Vibration

102

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This paper presents an experimental study of the effect of trailing edge serrations on airfoil instability noise. Detailed aeroacoustic measurements are presented of the noise radiated by an NACA-0012 airfoil with trailing edge serrations in a low to moderate speed flow under acoustical free field conditions. The existence of a separated boundary layer near the trailing edge of the airfoil at an angle of attack of 4.2 degree has been experimentally identified by a surface mounted hot-film arrays technique. Hot-wire results have shown that the saw-tooth surface can trigger a bypass transition and prevent the boundary layer from becoming separated. Without the separated boundary layer to act as an amplifier for the incoming Tollmien-Schlichting waves, the intensity and spectral characteristic of the radiated tonal noise can be affected depending upon the serration geometry. Particle Imaging Velocimetry (PIV) measurements of the airfoil wakes for a straight and serrated trailing edge are also reported in this paper. These measurements show that localized normal-component velocity fluctuations that are present in a small region of the wake from the laminar airfoil become weakened once serrations are introduced. Owing to the above unique characteristics of the serrated trailing edges, we are able to further investigate the mechanisms of airfoil instability tonal noise with special emphasis on the assessment of the wake and non-wake based aeroacoustic feedback model. It has been shown that the instability tonal noise generated at an angle of attack below approximately one degree could involve several complex mechanisms. On the other hand, the non-wake based aeroacoustic feedback mechanism alone is sufficient to predict all discrete tone frequencies accurately when the airfoil is at a moderate angle of attack.

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Section: 4supporting

confidence: 69%

“…1). Based solely on Model A, the tonal frequencies can be predicted [2,3,5] from the frequencies, f n , at which the phase change around the loop 2F(f n ), given by…”

Section: Assessment Of Feedback Mechanism Based On Model Amentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

An experimental study of airfoil instability tonal noise with trailing edge serrations

Chong¹,

Joseph²

2013

Journal of Sound and Vibration

102

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“…This was followed by an identification of multiple frequency peaks (see, e.g. Arbey & Bataille, 1983) and a resulting ladder structure as the free-stream velocity is varied. The multi-peak structure has been confirmed in further experiments as well as in numerical simulations by, e.g., Desquesnes et al (2007); Jones & Sandberg (2011);Fosas de Pando et al (2014) and has been linked to feedback loops consisting of boundary layer instabilities and acoustic radiation.…”

Section: Introductionmentioning

confidence: 99%

On the receptivity of aerofoil tonal noise: an adjoint analysis

Pando

Schmid

Sipp³

2017

J. Fluid Mech.

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(Received ?; revised ?; accepted ?. -To be entered by editorial office)For moderate-to-high Reynolds numbers, aerofoils are known to produce substantial levels of acoustic radiation, known as tonal noise, which arises from a complex interplay between laminar boundary-layer instabilities, trailing-edge acoustic scattering and upstream receptivity of the boundary layers on both aerofoil surfaces. The resulting acoustic spectrum is commonly characterised by distinct equally-spaced peaks encompassing the frequency range of convectively-amplified instability waves in the pressuresurface boundary-layer. In this work, we assess the receptivity and sensitivity of the flow by means of global stability theory and adjoint methods which are discussed in light of the spatial structure of the adjoint global modes as well as the wave-maker region. It is found that for the frequency range corresponding to acoustic tones the direct global modes capture the growth of instability waves on the suction surface and the near wake together with acoustic radiation into the far field. Conversely, it is shown that the corresponding adjoint global modes, which capture the most receptive region in the flow to external perturbations, have compact spatial support in the pressure surface boundarylayer, upstream of the separated flow region. Furthermore, we find that the relative spatial amplitude of the adjoint modes is higher for those modes whose real frequencies correspond to the acoustic peaks. Finally, the analysis of the wave-maker region points at the pressure surface near 30% of chord as the preferred zone for the placement of actuators for flow control of tonal noise.

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Noise Generation

2017

Wind Farm Noise: Measurement, Assessment

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Noise generated by airfoil profiles placed in a uniform laminar flow

Cited by 276 publications

References 13 publications

An experimental study of airfoil instability tonal noise with trailing edge serrations

An experimental study of airfoil instability tonal noise with trailing edge serrations

On the receptivity of aerofoil tonal noise: an adjoint analysis

Noise Generation

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