Scattering of turbulent-jet wavepackets by a swept trailing edge

Piantanida, Selene; Jaunet, Vincent; Jordan, Peter; Huber, Jérôme; Cavalieri, André V. G.; Wolf, William

doi:10.2514/6.2015-2998

Cited by 26 publications

(26 citation statements)

References 13 publications

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“…This is especially true when an aircraft is taking off. While the exact role played by jet instabilities in noise generation is still open to some debate for subsonic jets, recent studies (Cavalieri et al 2014;Piantanida et al 2016;Lyu & Dowling 2016;Lyu et al 2017) show that installed jet noise is dominated by the scattering of jet instability waves by the trailing edge of aircraft wings or flaps. To suppress or reduce installed jet noise, one can examine the possibility of controlling these instability waves.…”

Section: Introductionmentioning

confidence: 99%

Temporal stability analysis of jets of lobed geometry

Lyu

Dowling

2018

J. Fluid Mech.

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A 2D temporal incompressible stability analysis is carried out for lobed jets. The jet base flow is assumed to be parallel and of a vortex-sheet type. The eigenfunctions of this simplified stability problem are expanded using the eigenfunctions of a round jet.The original problem is then formulated as an innovative matrix eigenvalue problem, which can be solved in a very robust and efficient manner. The results show that the lobed geometry changes both the convection velocity and temporal growth rate of the instability waves. However, different modes are affected differently. In particular, mode 0 is not sensitive to the geometry changes, while modes of higher-orders can be changed significantly. The changes become more pronounced as the number of lobes N and the penetration ratio ǫ increase. Moreover, the lobed geometry can cause a previously degenerate eigenvalue (λ n = λ −n ) to become non-degenerate (λ n = λ −n ) and lead to opposite changes to the stability characteristics of the corresponding symmetric (n) and antisymmetric (−n) modes. It is also shown that each eigen-mode changes its shape in response to the lobes of the vortex sheet, and the degeneracy of an eigenvalue occurs when the vortex sheet has more symmetric planes than the corresponding mode shape (including both symmetric and antisymmetric planes). The new approach developed in this paper can be used to study the stability characteristics of jets of other arbitrary geometries in a robust and efficient manner.

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Section: Introductionmentioning

confidence: 99%

Temporal stability analysis of jets of lobed geometry

Lyu

Dowling

2018

J. Fluid Mech.

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“…Similar to the approach used by Papamoschou, 14 Cavalieri et al 15 proposed a wave-packet scattering model, and the far-field sound was calculated using a numerical Green's function integration and a Boundary Elemment Method (BEM). The same two modelling strategies were used by Piantanida et al 16 to model the installed jet noise from aircraft wings with swept trailing edges. In both studies, a good overall agreement for the noise directivity was observed at a few discrete frequencies.…”

Section: Introductionmentioning

confidence: 99%

“…Following Piantanida et al, 19 the idea of using swept aircraft wings to reduce installed jet noise was further explored by Nogueira, Cavalieri, and Jordan. 20 As an other attempt, Bastos, Deschamps, and da Silva 21 investigated the effects of chevron nozzles on installed jet noise.…”

Section: Introductionmentioning

confidence: 99%

Experimental validation of the hybrid scattering model of installed jet noise

Lyu

Dowling

2018

Physics of Fluids

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Jet installation causes jet noise to be amplified significantly at low frequencies and its physical mechanism must be understood to develop effective aircraft noise reduction strategies. A hybrid semi-empirical prediction model has recently been developed based on the instability-wave-scattering mechanism. However, its validity and accuracy remain to be tested. To do so, in this paper we carry out a systematic installed jet-noise experiment in the laboratory using a flat plate instead of an aircraft wing. We show that reducing H (the separation distance between the flat plate and jet centreline) causes stronger low-frequency noise enhancement while resulting in little change to the noise shielding and enhancement at high frequencies.Decreasing L (the axial distance between the jet exit plane and the trailing edge of the plate) results in reduced noise amplification at low frequencies and also weakens both the shielding and enhancement at high frequencies.Increasing the jet Mach number abates the installation effects. It is shown that the hybrid model developed in the earlier work agrees with experimental measurements and can capture the effects of varying H, L and jet Mach number extremely well. It is concluded that the model captures the correct physics and can serve as an accurate and robust prediction tool. This new physical understanding provides insights into innovative strategies for suppressing installed jet noise. a) bl362@cam.ac.uk 1 arXiv:1808.00086v1 [physics.flu-dyn] 31 Jul 2018

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“…Thus these models were inherently unable to capture detailed characteristics of installed jet noise correctly or to enhance physical understanding of the mechanisms. However, very recently some less-empirical models were proposed, including the work of Vera et al (2015) and Piantanida et al (2015). In Vera's work, for an assumed plane-wave-like incident field the scattered pressure on the surface of a semi-infinite flat plate is obtained by making use of Wiener-Hopf method and the far-field sound is obtained using Amiet's approach.…”

Section: Introductionmentioning

confidence: 99%

“…In addition the ambient flow (non-trivial in a real flight certification process) is neglected in their modelling. Piantanida et al (2015) adopted another approach in their work, where the half-plane scattering Green's function and an inferred near-field pressure source of the wave-packet form were used. The far-field sound is obtained by performing numerical integration.…”

Section: Introductionmentioning

confidence: 99%

Prediction of installed jet noise

2016

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A semi-analytical model for installed jet noise is proposed in this paper. We argue and conclude that there exist two distinct sound source mechanisms for installed jet noise and the model is therefore composed of two parts to account for these different sound source mechanisms. Lighthill's acoustic analogy and a fourth-order space-time correlation model for Lighthill stress tensor are used to model the sound induced by the equivalent turbulent quadrupole sources, while the trailing-edge scattering of near-field evanescent instability waves are modelled using Amiet's approach. A non-zero ambient mean flow is taken into account. It is found that, when the rigid surface is not so close to the jet as to affect the turbulent flow field, the trailing-edge scattering of near-field evanescent waves dominates the low frequency amplification of installed jet noise in the far-field. The high-frequency noise enhancement on the reflected side is due to the surface reflection effect. The model agrees well with experimental results at different observer angles apart from deviations caused by mean-flow refraction effect at high frequencies at low observer angles.

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Scattering of turbulent-jet wavepackets by a swept trailing edge

Cited by 26 publications

References 13 publications

Temporal stability analysis of jets of lobed geometry

Temporal stability analysis of jets of lobed geometry

Experimental validation of the hybrid scattering model of installed jet noise

Prediction of installed jet noise

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