A model problem for sound radiation by an installed jet

Nogueira, Petrônio A. S.; Cavalieri, André V. G.; Jordan, Peter

doi:10.1016/j.jsv.2016.12.015

Cited by 55 publications

(32 citation statements)

References 21 publications

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“…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. They found that the installed jet noise was not sensitive to the chevron geometries when the aircraft wing was close to the jet, though an overall slight noise reduction could be achieved when they were away from each other.…”

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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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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“…The content of the Green's functions in the wavenumber space are different 12,13 , which would permit source wavenumbers that are evanescent in the free-field case to generate farfield noise when the jet is close to a flat plate. Slight changes in wave-packet envelope or coherence decay may influence free-jet noise substantially 13 , and lead to little changes for installed jets 12 . That is possibly why the results with the plate were in good agreement with the reference data, despite of the problems observed in the free-jet case.…”

Section: A Two-dimensional Source Modelmentioning

confidence: 99%

“…Further studies are needed to evaluate the pertinence of the model, and it would be important to use data from jet turbulence to construct a source. Moreover the role of jitter/coherence decay is apparently weaker in installed jet noise according to Nogueira et al 12 , but the cited work dealt with a model problem. Again, the use of turbulence data may help addressing this question in a more definite way.…”

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confidence: 99%

“…Several experimental and theoretical studies highlighted the importance of such structures in jet noise [5][6][7][8] . Theoretical models based on wavepackets have been shown to capture many of the main characteristics of the far-field noise for isolated 8,9 and installed jet cases [10][11][12] . However, inconsistencies are present as the absolute noise levels are under predicted by linear dynamic models, such as the Parabolised Stability Equations.…”

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confidence: 99%

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On the modelling of wavepacket scattering noise with coherence effects

Silva

Jordan

Cavalieri

2019

The Journal of the Acoustical Society of America

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An investigation of a wavepacket model for free-jet and jet-surface interaction noise was conducted. The source term for the axisymmetric mode was extracted from a Mach 0.9 jet large eddy simulation and employed to adjust the parameters of a simple source model. Streamwise coherence decay, in particular, was considered. The source model was propagated with both the free-field and tailored Green's function for a semi-infinite flat plate positioned at a distance of r/D = 1 from the jet axis. Significant deviations were observed in the prediction of the low-angle directivity of the isolated jet as well as in the reproduction of the characteristics of the source field. However, the effects of trailing edge noise were well reproduced. The installed jet case, at the region dominated by trailing-edge scattering, showed very little sensitivity to the coherence decay, a crucial feature in the isolated jet case. In this sense, the modelling of the installed-jet case proved to be much simpler.

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“…It however remained to be shown how the model can capture the far-field sound at other frequencies and how the non-axisymmetric azimuthal modes of the wave-packets contribute to the far-field. The contribution of non-axisymmetric wavepackets to the far-field noise was studied in the recent work of Nogueira et al (2017) using a similar Green's function approach. It was shown that the non-axisymmetric wavepackets were less efficient in contributing to the far-field sound than the axisymmetric mode.…”

Section: Introductionmentioning

confidence: 99%

Modelling installed jet noise due to the scattering of jet instability waves by swept wings

Lyu

Dowling

2019

J. Fluid Mech.

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Jet noise is a significant contributor to aircraft noise, and on modern aircraft it is considerably enhanced at low frequencies by a closely installed wing. Recent research has shown that this noise increase is due to the scattering of jet instability waves by the trailing edge of the wing. Experimentalists have recently shown that noise can be reduced by using wings with swept trailing edges. To understand this mechanism, in this paper, we develop an analytical model to predict the installed jet noise due to the scattering of instability waves by a swept wing. The model is based on the Schwarzschild method and Amiet’s approach is used to obtain the far-field sound. The model can correctly predict both the reduction in installed jet noise and the change to directivity patterns observed in experiments due to the use of swept wings. The agreement between the model and experiment is very good, especially for the directivity at large azimuthal angles. It is found that the principal physical mechanism of sound reduction is due to destructive interference. It is concluded that in order to obtain an effective noise reduction, both the span and the sweep angle of the wing have to be large. Such a model can greatly aid in the design of quieter swept wings and the physical mechanism identified can provide significant insight into developing other innovative noise-reduction strategies.

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A model problem for sound radiation by an installed jet

Cited by 55 publications

References 21 publications

Experimental validation of the hybrid scattering model of installed jet noise

Experimental validation of the hybrid scattering model of installed jet noise

On the modelling of wavepacket scattering noise with coherence effects

Modelling installed jet noise due to the scattering of jet instability waves by swept wings

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