Analytical, numerical and experimental investigation of trailing-edge noise reduction on a Controlled Diffusion airfoil with serrations

Moreau, Stéphane; Sanjosé, Marlène; Lyu, Benshuai; Ayton, Lorna J.

doi:10.2514/6.2019-2450

Cited by 17 publications

(18 citation statements)

References 35 publications

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“…The break-up of the large-scale vortices is also reported in other papers (Ji et al 2014;Sanjosé et al 2014). To provide more insights into the theoretical models developed recently, Moreau et al (2019) conducted an experimental and DNS investigation on the control diffusion airfoil with serrated add ons, which confirmed that the turbulent boundary layer statistics were not largely modified. It was also shown that Lyu et al's (2016) and Ayton's (2018) models agreed better with the computational results, while Howe's (1991) in fact overpredicted the noise reduction.…”

Section: Introductionsupporting

confidence: 70%

Noise reduction mechanisms for insert-type serrations of the NACA-0012 airfoil

Wan

et al. 2022

J. Fluid Mech.

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Trailing-edge serrations inspired by owls are capable of reducing broadband noise. In this study, the wall-resolved large-eddy simulations (LES) are carried out on the flow over NACA-0012 airfoil with additional serrated trailing edges. The computations are conducted with the high-order flux reconstruction method on unstructured meshes. Three kinds of serrations with different lengths are studied and compared with the straight trailing-edge case, and all three types of serration achieved a certain degree of noise reduction. Presently, the medium-length serration achieves the best noise reduction effect. The maximum decrease of overall sound pressure level is approximately 2.4 dB, implying that the length of serration has a substantial impact on the noise reduction effect. The serration has no significant effect on the upstream turbulence statistics, but it changes the flow structure near the serration, such as inducing side vortex pairs attached to the serration edges. Moreover, dynamic mode decomposition shows that the pressure structures vary with the serration length. For the most unstable hydrodynamic wave, the spanwise coherence of the mode structure of pressure in the upstream boundary layer is weakened. In addition, serrations can redistribute the dipole sources on the surfaces of airfoil and serrations. The destructive interference is enhanced to some extent, which is favourable for noise reduction. In contrast with LES simulations, the pure dipole analysis shows that the longest serration case seems to be the best. Furthermore, a recently developed noise theory is used to evaluate the influence of serrations on the flow noise sources qualitatively and quantitatively. It is found that the serrations can mitigate noise source intensity near the serration edges but increase the source intensity in the near wake. The combined effect of serration on the dipole source and flow noise source determines the overall noise reduction effect. To conclude, destructive interference plays a primary role in suppressing noise radiation by serrated trailing edges, and the dual effect of flow noise sources should be considered in future serration designs. As the influence of turbulence structure will make it more difficult to find the optimal serration parameters, the position of high-fidelity simulation will become increasingly important.

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Section: Introductionsupporting

confidence: 70%

Noise reduction mechanisms for insert-type serrations of the NACA-0012 airfoil

Wan

et al. 2022

J. Fluid Mech.

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“…In some configurations of angle of attack and flow velocity the sound obviously exhibits transient features such as intermittency or bifurcations from one of alternate states to the other. Firstly, this could explain discrepancies between measurements and numerical simulations because the simulated signals are generally very short, except in the recent LBM DNS [39,40]. Secondly, the usual Fourier transform could be misleading because of its inherent averaging procedure.…”

Section: Time-frequency Analysismentioning

confidence: 99%

Experimental and Analytical Investigation of the Tonal Trailing-Edge Noise Radiated by Low Reynolds Number Aerofoils

et al. 2020

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An experimental and analytical study of the tonal trailing-edge noise of a symmetric NACA-0012 aerofoil and of a cambered SD7003 aerofoil has been achieved. It provides a complete experimental database for both aerofoils and improves the understanding of the underlying mechanisms. The analysis stresses the high sensitivity of the tonal noise phenomenon to the flow velocity and the angle of attack. Several regimes of the noise emission are observed depending on the aforementioned parameters. The contributions of the pressure and the suction sides are found to vary with the flow parameters too. A special attention has been paid to the role of the separation bubble in the tonal noise generation. Hot-wire measurements and flow visualization prove that the separation bubble is a necessary condition for the tonal noise production. Moreover, the bubble must be located close enough to the trailing edge. Several tests with small-scale upstream turbulence confirm the existence of the feedback loop. Analytical predictions with a classical trailing-edge noise model show a good agreement with the experimental data; they confirm the cause-to-effect relationship between the wall-pressure fluctuations and the radiated sound. Finally, previously reported works on fans and propellers are shortly re-addressed to show that the tonal noise associated with laminar-boundary-layer instabilities can take place in rotating blade technology.

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“…This is also representative of the little influence of residual inlet turbulence (below 0.4%) observed in various wind-tunnels on the separation bubble size on the CD airfoil. 37 The initial condition for the simulation was taken from a preliminary simulation on a coarser grid with the first two finer VRs removed. The fully resolved simulation has been run for a total of 50 flow-through times, the first 10 flow-through times being a transient period to establish the flow field in the computational domain.…”

Section: Numerical Set-upmentioning

confidence: 99%

Modal analysis of the laminar boundary layer instability and tonal noise of an airfoil at Reynolds number 150,000

Sanjosé

Towne

Jaiswal

et al. 2018

International Journal of Aeroacoustics

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A direct numerical simulation of the flow field around a controlled-diffusion airfoil within an anechoic wind-tunnel at 5 • incidence and a high Reynolds number of 1.5 × 10 5 is performed for the first time using a Lattice Boltzmann Method. The simulation compares favorably with experimental measurements of wall-pressure, wake statistics, and far-field sound. The simulation noticeably captures experimentally observed high-amplitude acoustic tones that rise above a broadband hump. Both noise components are related to a breathing of a recirculation bubble formed around 65-70% of the chord, and to Kelvin-Helmholtz instabilities in the separated shear layer that yield rollers that break down into turbulent vortices whose diffraction at the trailing edge produces a strong dipole acoustic field. A wavelet analysis of the wall-pressure signals combined with some flow visualization has shown that the flow statistics are dominated by intense events caused by intermittent, large and intense bursting rollers. Several modal analyses of these events are performed on both the wall pressure fluctuations and the span averaged flow field in order to analyse the boundary layer instability which triggers the typical sharp tones over a broadband hump in airfoil noise. A suction side Kelvin-Helmholtz instability is observed to be coupled with a pressure side vortex shedding induced by the sudden transition to turbulence and the blunt trailing edge.

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Analytical, numerical and experimental investigation of trailing-edge noise reduction on a Controlled Diffusion airfoil with serrations

Cited by 17 publications

References 35 publications

Noise reduction mechanisms for insert-type serrations of the NACA-0012 airfoil

Noise reduction mechanisms for insert-type serrations of the NACA-0012 airfoil

Experimental and Analytical Investigation of the Tonal Trailing-Edge Noise Radiated by Low Reynolds Number Aerofoils

Modal analysis of the laminar boundary layer instability and tonal noise of an airfoil at Reynolds number 150,000

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