Symmetric airfoil geometry effects on leading edge noise

Gill, James; Xin, Zhang; Joseph, Phillip

doi:10.1121/1.4818769

Cited by 93 publications

(112 citation statements)

References 28 publications

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“…The noise generated by aerodynamic bodies in fluid flow has motivated significant research for decades, ranging from simple analytical models for flat plates in uniform flow with unsteady perturbations (Amiet 1975) to high-fidelity numerical models that predict the noise generated by turbulent interactions with realistic thick aerofoils (Gill et al 2013;Allampalli et al 2009;Lockard & Morris 1998;Kim & Haeri 2015). A particularly important and unavoidable source of aerofoil noise is so-called trailing-edge noise which is generated by turbulence in the boundary layer scattering off the sharp trailing edge of an aerofoil.…”

Section: Introductionmentioning

confidence: 99%

Aerodynamic noise from rigid trailing edges with finite porous extensions

Kisil

Ayton

2017

J. Fluid Mech.

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This paper investigates the effects of finite flat porous extensions to semi-infinite impermeable flat plates in an attempt to control trailing-edge noise through bio-inspired adaptations. Specifically the problem of sound generated by a gust convecting in uniform mean steady flow scattering off the trailing edge and permeable-impermeable junction is considered. This setup supposes that any realistic trailing-edge adaptation to a blade would be sufficiently small so that the turbulent boundary layer encapsulates both the porous edge and the permeable-impermeable junction, and therefore the interaction of acoustics generated at these two discontinuous boundaries is important. The acoustic problem is tackled analytically through use of the Wiener-Hopf method. A two-dimensional matrix Wiener-Hopf problem arises due to the two interaction points (the trailing edge and the permeable-impermeable junction). This paper discusses a new iterative method for solving this matrix Wiener-Hopf equation which extends to further two-dimensional problems in particular those involving analytic terms that exponentially grow in the upper or lower half planes. This method is an extension of the commonly used "pole removal" technique and avoids the needs for full matrix factorisation. Convergence of this iterative method to an exact solution is shown to be particularly fast when terms neglected in the second step are formally smaller than all other terms retained. The new method is validated by comparing the iterative solutions for acoustic scattering by a finite impermeable plate against a known solution (obtained in terms of Mathieu functions). The final acoustic solution highlights the effects of the permeable-impermeable junction on the generated noise, in particular how this junction affects the far-field noise generated by high-frequency gusts by creating an interference to typical trailing-edge scattering. This effect results in partially porous plates predicting a lower noise reduction than fully porous plates when compared to fully impermeable plates.

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Section: Introductionmentioning

confidence: 99%

Aerodynamic noise from rigid trailing edges with finite porous extensions

Kisil

Ayton

2017

J. Fluid Mech.

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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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“…The effects of variations in aerofoil geometry such as angle of attack, aerofoil thickness, camber, etc, on ATI noise have been studied by Atassi et al (1990), Lockard & Morris (1998), Evers & Peake (2002), Devenport et al (2010), Roger & Moreau (2010), Roger & Carazo (2010), Gill et al (2013), Ayton & Peake (2013) and . Most of this work has been based on two-dimensional turbulence or harmonic vortical gusts at low freestream Mach numbers.…”

Section: Introductionmentioning

confidence: 99%

On the reduction of aerofoil–turbulence interaction noise associated with wavy leading edges

2016

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An aerofoil leading-edge profile based on wavy (sinusoidal) protuberances/tubercles is investigated to understand the mechanisms by which they are able to reduce the noise produced through the interaction with turbulent mean flow. Numerical simulations are performed for non-lifting flat-plate aerofoils with straight and wavy leading edges (denoted by SLE and WLE, respectively) subjected to impinging turbulence that is synthetically generated in the upstream zone (freestream Mach number of 0.24). Full threedimensional Euler (inviscid) solutions are computed for this study thereby eliminating self-noise components. A high-order accurate finite-difference method and artefact-free boundary conditions are used in the current simulations. Various statistical analysis methods, including frequency spectra, are implemented to aid the understanding of the noise-reduction mechanisms. It is found with WLEs, unlike the SLE, that the surface pressure fluctuations along the leading edge exhibit a significant source cut-off effect due to geometric obliqueness which leads to reduced levels of radiated sound pressure. It is also found that there exists a phase interference effect particularly prevalent between the peak and the hill centre of the WLE geometry, which contributes to the noise reduction in the mid-to high-frequency range.

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Symmetric airfoil geometry effects on leading edge noise

Cited by 93 publications

References 28 publications

Aerodynamic noise from rigid trailing edges with finite porous extensions

Aerodynamic noise from rigid trailing edges with finite porous extensions

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

On the reduction of aerofoil–turbulence interaction noise associated with wavy leading edges

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