Experimental Investigation of Airfoil Self Noise and Turbulent Wake Reduction by the use of Trailing Edge Serrations

Gruber, Mathieu; Joseph, P.F.; Chong, Tze Pei

doi:10.2514/6.2010-3803

Cited by 88 publications

(79 citation statements)

References 10 publications

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“…This can be explained by the fact that the characteristic time scale of a vortex moving past the sharp leading edge is several orders of magnitude smaller than the integral time scale of the turbulence. This would need however to be re-examined for realistic airfoils where the leading edge has a finite radius of curvature, for instance using experimental data from Paterson & Amiet [35], Devenport et al [36] or Gruber & Joseph [37,38]. Note that although all the validation examples presented here are against analytical solutions, comparisons with experimental data have been presented in [20], but they were not sufficiently conclusive as far as the effect of the integral time scale is concerned, mainly because the numerical simulations were using a flat plate.…”

Section: Discussionmentioning

confidence: 99%

Random particle methods applied to broadband fan interaction noise

Dieste

Gabard

2012

Journal of Computational Physics

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Predicting broadband fan noise is key to reduce noise emissions from aircraft and wind turbines. Complete CFD simulations of broadband fan noise generation remain too expensive to be used routinely for engineering design. A more efficient approach consists in synthesizing a turbulent velocity field that captures the main features of the exact solution. This synthetic turbulence is then used in a noise source model. This paper concentrates on predicting broadband fan noise interaction (also called leading edge noise) and demonstrates that a Random Particle Mesh method (RPM) is well suited for simulating this source mechanism. The linearized Euler equations are used to describe sound generation and propagation. In this work, the definition of the filter kernel is generalized to include non-Gaussian filters that can directly follow more realistic energy spectra such as the ones developed by Liepmann and von Kármán. The velocity correlation and energy spectrum of the turbulence are found to be well captured by the RPM. The acoustic predictions are successfully validated against Amiet's analytical solution for a flat plate in a turbulent stream. A standard Langevin equation is used to model temporal decorrelation, but the presence of numerical issues leads to the introduction and validation of a second-order Langevin model.

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Section: Discussionmentioning

confidence: 99%

Random particle methods applied to broadband fan interaction noise

Dieste

Gabard

2012

Journal of Computational Physics

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“…Lyu et al 13 further developed a new semi-analytical model applying the Schwarzschild method of propagation of the pressure fluctuations. Although closer to reality, the final result does not allow yet to explain some of the physical features already at zero angle of attack such as the characteristic cross-over frequency St δ = fδ/V ∞ ≈ 1 (based on the free-stream velocity V ∞ and boundary-layer thickness δ, from XFOIL) 14 after which noise increases again. It was recently showed that one of the limitation of the theoretical model is the assumption of frozen turbulence along the serration length.…”

Section: Introductionmentioning

confidence: 99%

Near-wall pressure fluctuations over noise reduction add-ons

Avallone

Velden

Martinez

et al. 2017

23rd AIAA/CEAS Aeroacoustics Conference

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The hydrodynamic pressure fluctuations over the suction side of a NACA 0018 airfoil with trailing-edge add-ons are obtained from integration of time-resolved stereoscopic particle image velocimetry data and compared to ones computed with the Lattice Boltzmann method. The airfoil is retrofitted with solid and slitted serrated trailing edges. Analysis of the data confirms that the intensity of the pressure fluctuations along the edge of the serrations decreases from the root to the tip. Spectra of the pressure fluctuations vary in the stream-wise direction, which might be caused by the shear at the edge of the serration and by the flow seeping through the empty space in-between them. Results from slitted serrations show that they enhance the intensity of the pressure fluctuations at the root, with critical repercussion on their effectiveness in noise reduction.

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“…The model predicts an asymptotic noise reduction value at high frequency of 10log 10 [1 + (4h/b) 2 overestimates the magnitude of the noise reduction with serration add-ons. Moreover, the model is not suitable for predicting the characteristic frequency St δ = f δ/U ∞ ≈ 1 (based on the free-stream velocity U ∞ and boundary layer thickness δ estimated with XFOIL in the study of Gruber et al 26 ) after which noise increases again.…”

Section: Introductionmentioning

confidence: 99%

“…It may also clarify the discrepancies between measured and predicted noise reduction reported in previous studies. Until now, a link between flow measurements 13,26,36 and their aeroacoustics footprint is missing. Clemons and Wlezien 36 used hot-wire anemometry to measure the convective velocity and spanwise correlation length of the streamwise velocity turbulent fluctuations.…”

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confidence: 99%

Three-dimensional flow field over a trailing-edge serration and implications on broadband noise

2016

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The three-dimensional flow field over the suction side of a NACA 0018 airfoil with trailing-edge serrations was studied by means of time-resolved tomographic particle image velocimetry. Mean flow results show that the boundary layer thickness decreases along the streamwise direction with a corresponding reduction of the size of the turbulent structures developing over the suction side of the serrations. At a positive angle of attack, streamwise-oriented and counter-rotating vortices aligned with the edge of the serrations are found to be the main features of the mean flow field. Their formation is attributed to the pressure imbalance between the two sides of the airfoil and the mixing layer at the edge. They locally modify the effective angle seen by the turbulent flow approaching the serrated edge. This effect may contribute to the serration underperformance in terms of noise reduction reported in literature. The spatial distribution of the spectra of the source term of the Poisson equation, which relates the velocity field to pressure fluctuations, suggests that the contribution of the serrations to far-field broadband noise is a function of the streamwise location. This observation is congruent with the spectra of the wall-normal and spanwise velocity fluctuations, which typically show low intensity close to the tips of the individual serrations. It follows that analytical models must take into account the local contribution to the far-field noise induced by the streamwise variation of the hydrodynamic pressure on the serration surface.

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Experimental Investigation of Airfoil Self Noise and Turbulent Wake Reduction by the use of Trailing Edge Serrations

Cited by 88 publications

References 10 publications

Random particle methods applied to broadband fan interaction noise

Random particle methods applied to broadband fan interaction noise

Near-wall pressure fluctuations over noise reduction add-ons

Three-dimensional flow field over a trailing-edge serration and implications on broadband noise

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