Leading Edge Noise from Thick Foils in Turbulent Flows

Gershfeld, Jonathan

doi:10.21236/ada418125

Cited by 18 publications

(24 citation statements)

References 7 publications

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“…The effects of aerofoil geometry on turbulence-aerofoil interaction noise has been studied extensively (Gershfeld 2004;Roger 2010;Moriarty et al 2005;Lysak et al 2013;Gill et al 2013;Devenport et al 2010;Evers & Peake 2002;Chaitanya et al 2015a). It has been demonstrated by the authors of the current paper Haeri et al 2014;Narayanan et al 2015;Chaitanya et al 2015b;Kim et al 2016) and others that introducing leading edge serrations can be an effective method of reducing far field noise.…”

Section: Introductionmentioning

confidence: 99%

Performance and mechanism of sinusoidal leading edge serrations for the reduction of turbulence–aerofoil interaction noise

et al. 2017

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This paper presents the results of a detailed experimental investigation into the effectiveness of sinusoidal leading edge serrations on aerofoils for the reduction of the noise generated by the interaction with turbulent flow. A detailed parametric study is performed to investigate the sensitivity of the noise reductions to the serration amplitude and wavelength. The study is primarily performed on flat plates in an idealized turbulent flow, which we demonstrate captures the same behaviour as when identical serrations are introduced onto 3D aerofoils. The influence on the noise reduction of the turbulence integral length-scale is also studied. An optimum serration wavelength is identified whereby maximum noise reductions are obtained, corresponding to when the transverse integral length-scale is roughly one-forth the serration wavelength. This paper proves that, at the optimum serration wavelength, adjacent valley sources are excited incoherently. One of the most important findings of this paper is that, at the optimum serration wavelength, the sound power radiation from the serrated aerofoil varies inversely proportional to the Strouhal number St h = f h U , where f , h and U are frequency, serration amplitude and flow speed, respectively. A simple model is proposed to explain this behaviour. Noise reductions are observed to generally increase with increasing frequency until the frequency at which aerofoil self-noise dominates the interaction noise. Leading edge serrations are also shown to reduce trailing edge self-noise. The mechanism for this phenomenon is explored through PIV measurements. Finally, the lift and drag of the serrated aerofoil are obtained through direct measurement and compared against the straight edge baseline aerofoil. It is shown that aerodynamic performance is not substantially degraded by the introduction of the leading edge serrations on the aerofoil.

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Section: Introductionmentioning

confidence: 99%

Performance and mechanism of sinusoidal leading edge serrations for the reduction of turbulence–aerofoil interaction noise

et al. 2017

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“…This is exploited with the use of cross spectral measurements on opposite sides of the foil to reject the incident fields so that the scattered surface pressures can be measured at higher frequencies where the thickness effect is pronounced. The surface pressure cross spectra showed the thickness correction to Seats' fimction [Gershfeld (2003)] tiiat was also observed in the far field from the dipole sound measurements of Amiet (1976,1977) and Olsen and Wagaer (1982). The thickness dependence of the dipole sound is only weakly dependent on the leading edge radius of curvature at the apex of tiie edge and is mainly a fimction of the foil's maximum section thickness.…”

Section: Discussionmentioning

confidence: 57%

“…Figures (1.1) and (1.2) [Gershfeld (2003)] show respectively, a comparison of the measured dipole sound from Amiet (1976,1977) and the predicted dipole sound for a foil with thickness to chord, c, ratio of zero (h/c=0), and with a thickness to chord ratio of the NACA 0012 section, h/c=0.12. The thickness effect is incorporated in the near field portion of the Green fimction that determines, in part, the net dipole force associated with the acoustic radiation from the diffraction of turbulence by an edge of a given geometry [Howe (1998a, b)].…”

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confidence: 99%

“…Therefore, the diffracted pressures from the thick foil do not couple directly to the normalized wave number spectrum of the incident up-wash velocity, ^(k2), in the thickness direction (2) except indirectly at k2=0. Gershfeld (2003) has shown that the incident pressures depend on the integral length scale of the up-wash velocity component in the thickness direction, yn:=^(k2 =0). The diffracted pressures must also depend on ^(A:2=0) since they are proportional to the incident pressures.…”

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confidence: 99%

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Leading Edge Surface Pressures from Airfoils in a Turbulent Flow

Gershfeld¹,

Mathews²

2004

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“…However, there have been attempts at extending the theory to include real geometry effects. By using a modified Greens function to account for plate thickness, Gershfeld 11 showed that radiated sound due to turbulent flow at high frequencies could be reduced by increasing the finite thickness of a flat plate. Glegg and Devenport…”

Section: Iia Experimental Studiesmentioning

confidence: 99%

Reduced Dimension Modeling of Leading Edge Turbulent Interaction Noise

Gill

Zhang

Joseph

et al. 2014

20th AIAA/CEAS Aeroacoustics Conference

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A computational aeroacoustics approach is used to model the effects of real airfoil geometry on leading edge turbulent interaction noise for symmetric airfoils at zero angle of attack. For the first time, one-component (transverse), two-component (transverse and streamwise), and three-component (transverse, streamwise, and spanwise) synthesized turbulent disturbances are modeled instead of single frequency transverse gusts, which previous computational studies of leading edge noise have been confined to. The effects of the inclusion of streamwise and spanwise disturbances on the noise are assessed, and it is shown that accurate noise predictions for symmetric airfoils can be made by modeling only the transverse disturbances, which reduces the computational expense of simulations. Additionally, the two-component turbulent synthesis method is used to model the effects of airfoil thickness on the noise for thicknesses ranging from 2% to 12%. By using sufficient airfoil thicknesses to show trends, it is found that airfoil thickness will reduce the noise at high frequency, and that the sound power P will reduce linearly with increasing airfoil thickness. Keywords

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Leading Edge Noise from Thick Foils in Turbulent Flows

Cited by 18 publications

References 7 publications

Performance and mechanism of sinusoidal leading edge serrations for the reduction of turbulence–aerofoil interaction noise

Performance and mechanism of sinusoidal leading edge serrations for the reduction of turbulence–aerofoil interaction noise

Leading Edge Surface Pressures from Airfoils in a Turbulent Flow

Reduced Dimension Modeling of Leading Edge Turbulent Interaction Noise

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