Aeroacoustic source mechanisms of a wavy leading edge undergoing vortical disturbances

Turner, Jacob; Kim, Jae Wook

doi:10.1017/jfm.2016.785

Cited by 68 publications

(39 citation statements)

References 42 publications

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“…Previous work on single-wavelength profiles indicate that the dominant sources are located at the root region Kim et al (2016);Chaitanya et al (2017);Gea-Aguilera et al (2017). The reason for this behaviour has been investigated by Turner and Kim (2017). They showed that the root of the serrated leading edge is the dominant noise source due to the presence of a secondary horseshoe-like vortex system generated by the serrated leading edge, which alters the upstream velocity field, thereby enhancing the source strength at the serration root.…”

Section: A Simple Analytical Model To Predict Noise Reductionsmentioning

confidence: 98%

Aerofoil geometry effects on turbulence interaction noise

Paruchuri

2015

21st AIAA/CEAS Aeroacoustics Conference

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Faculty of Engineering and the Environment Institute of Sound and Vibration Research Doctor of PhilosophyAerofoil geometry effects on turbulence interaction noise by Chaitanya PARUCHURI Fan broadband is one of the dominant noise sources on an aircraft engine, particularly at approach. The dominant noise generation mechanism is due to turbulent-aerofoil interaction noise (TAI). This thesis investigates the effect of changes in 2D aerofoil geometry on TAI noise. The main focus of this thesis is to attempt to reduce it through the development of innovative leading edge geometries. The first two chapters of the thesis deals with an experimental and numerical investigation into the effect of aerofoil geometry on interaction noise on single aerofoils and on cascades. Consistent with previous work, they show that variations in aerofoil parameters, such as aerofoil thickness, leading edge nose radius and camber, produce only a small changes in broadband interaction noise at approach conditions. Subsequent chapters deal with the development of innovative leading edge serration profiles aimed at reducing interaction noise. Chapter 4 is a detailed study into the limitations of single-wavelength serrations in reducing interaction noise. The optimum profile is identified. Chapters 5, 6 and 7 all deal with the development of innovative profiles that can provide up to 10dB of additional noise reductions compared to single-wavelength serrations. For each of the profiles investigated a simple model is developed to aid the understanding of their interaction mechanism. v

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Section: A Simple Analytical Model To Predict Noise Reductionsmentioning

confidence: 98%

Aerofoil geometry effects on turbulence interaction noise

Paruchuri

2015

21st AIAA/CEAS Aeroacoustics Conference

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“…However, most of these papers were focused on single-wavelength serrated leading edge profiles. The noise reduction mechanism of these profiles has been investigated in detail by [6,[10][11][12][18][19][20][21] and essentially involves a reduction in the source strength everywhere along the serrated leading edge except at the root location. At this location, it has been shown that the source strength per unit edge length is identical to that of a straight edge in [11].…”

Section: A Single-wavelengthmentioning

confidence: 99%

Leading-Edge Profiles for the Reduction of Airfoil Interaction Noise

2020

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Aerofoils operating in a turbulent flow are an efficient source of noise radiation by scattering vorticity into sound at the leading edge. Much work has been undertaken demonstrating the effectiveness by which serrations, or undulations, introduced onto the leading edge, can substantially reduce broadband leading edge interaction noise. However, most of this work is focused on sinusoidal leading edge serration profiles. In this paper, a family of serration profiles are proposed that are capable of providing significantly greater noise reductions than single-wavelength serrations at optimal conditions. This new family of profiles will be shown to reduce interaction noise through a fundamentally different noise reduction mechanism than conventional single-wavelength profiles. Unlike single-wavelength profiles, which produce a single compact dominant source region per serration wavelength, these new profiles are designed to produce two or more dominant compact sources per serration wavelength of roughly the same source strength, that are separated in the streamwise direction. Since these sources are arranged to be closer together than the turbulence length-scale, they are highly coherent and, at certain frequencies, radiate exactly 180 • out of phase leading to very high levels of noise reduction in the far field. The experimental noise reduction spectra are compared against an analytic model obtained as a solution of the acoustic wave equation using the Wiener-Hopf technique. This is shown to be unable to capture the main features of the noise reduction spectra as the source strength distribution for other profiles are not captured. A simple model has therefore been developed to explain the noise reduction mechanism for these new profiles, based on interference between sources distributed along the leading edge. Good qualitative agreement is obtained with the experimental results. * Research fellow, ccp1m17@soton.ac.uk † Professor, Senior member AIAA, pfj@soton.ac.uk ‡ EPSRC research fellow, member AIAA, lja30@cam.ac.uk

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“…The solution is found in Section 3 using separation of variables and the Wiener-Hopf technique. Section 4 contains results for the scattered acoustic far field which we compare to numerical simulations adapted from Turner & Kim (2017). A brief discussion of the adapted numerical method used is given in Section 4.5.…”

Section: Introductionmentioning

confidence: 99%

An analytic solution for the noise generated by gust–aerofoil interaction for plates with serrated leading edges

Ayton

Kim

2018

J. Fluid Mech.

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This paper presents an analytic solution for the sound generated by an unsteady gust interacting with a semi-infinite flat plate with a serrated leading edge in a background steady uniform flow. Viscous and nonlinear effects are neglected. The Wiener–Hopf method is used in conjunction with a non-orthogonal coordinate transformation and separation of variables to permit analytical progress. The solution is obtained in terms of a modal expansion in the spanwise coordinate; however, for low- and mid-range incident frequencies only the zeroth-order mode is seen to contribute to the far-field acoustics, therefore the far-field noise can be quickly evaluated. The solution gives insight into the potential mechanisms behind the reduction of noise for plates with serrated leading edges compared to those with straight edges, and predicts a logarithmic dependence between the tip-to-root serration height and the decrease of far-field noise. The two mechanisms behind the noise reduction are proposed to be an increased destructive interference in the far field, and a redistribution of acoustic energy from low cut-on modes to higher cut-off modes as the tip-to-root serration height is increased. The analytic results show good agreement in comparison with experimental measurements. The results are also compared against nonlinear numerical predictions where good agreement is also seen between the two results as frequency and tip-to-root ratio are varied.

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Aeroacoustic source mechanisms of a wavy leading edge undergoing vortical disturbances

Cited by 68 publications

References 42 publications

Aerofoil geometry effects on turbulence interaction noise

Aerofoil geometry effects on turbulence interaction noise

Leading-Edge Profiles for the Reduction of Airfoil Interaction Noise

An analytic solution for the noise generated by gust–aerofoil interaction for plates with serrated leading edges

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