Laminar boundary layer instability noise produced by an aerofoil

Kingan, Michael J.; Pearse, John

doi:10.1016/j.jsv.2008.11.043

Cited by 87 publications

(61 citation statements)

References 22 publications

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“…This mechanism is supported by a number of studies in which the frequencies of the maximum T-S wave amplification occur at frequencies that closely coincide with the frequencies of the main broadband hump [3][4][5]. Tam [6] has proposed that the scattering process at the trailing edge will form part of a closed aeroacoustic feedback loop, which is responsible for the generation of the multiple, high amplitude "tones".…”

Section: Introductionmentioning

confidence: 91%

“…Disturbances in the laminar boundary layer are assumed to be spatially growing two-dimensional T-S waves with fixed frequency and slowly changing complex wavenumber [4,5]. The wavenumber of the disturbances, , can be represented by:…”

Section: Linear Stability Analysis For the Two-dimensional Boundary Lmentioning

confidence: 99%

“…In this study, the boundary layer velocity profiles were obtained using a numerical method, which was originally developed and successfully implemented by Kingan and Pearse [5]. Calculation of the velocity profiles was made using the public domain code, XFOIL [22] to determine the shape factors and boundary layer displacement thicknesses over the airfoil surface.…”

Section: Linear Stability Analysis For the Two-dimensional Boundary Lmentioning

confidence: 99%

“…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

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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: Introductionmentioning

confidence: 91%

Section: Linear Stability Analysis For the Two-dimensional Boundary Lmentioning

confidence: 99%

Section: Linear Stability Analysis For the Two-dimensional Boundary Lmentioning

confidence: 99%

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

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“…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. Simplified theoretical models -relying on a phase condition between local spatial growth, acoustic scattering on the trailing edge and a receptivity process at a prescribed location -have been proposed by Kingan & Pearse (2009), which reproduced well the observed frequencies for the tonal noise problem. A recent experimental study (Pröbst-ing et al, 2014) has presented detailed time-resolved particle-image-velocimetry (PIV) measurements of acoustic sources near the trailing edge of the aerofoil, reporting that vortical structures, emanating from boundary layer instabilities, pass the trailing edge at the frequency of the dominant tone.…”

Section: Introductionmentioning

confidence: 73%

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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Laminar boundary layer instability noise produced by an aerofoil

Cited by 87 publications

References 22 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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