Farfield filtering and source imaging of subsonic jet noise

Koenig, Maxime; Cavalieri, André V. G.; Jordan, Peter; Delville, J.; Gervais, Yves; Papamoschou, Dimitri

doi:10.1016/j.jsv.2013.02.040

Cited by 48 publications

(36 citation statements)

References 31 publications

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“…This wave-packet behavior (Figure 9) is correlated with temporally localized bursts of sound in the far field (Cavalieri et al 2011a, Guj et al 2003, Hileman et al 2005, Juvé et al 1980, Kerhervé et al 2012b, Koenig et al 2012). Recent optimal-control studies provide further confirmation.…”

Section: Intermittency: Loud and Quiet Flowsmentioning

confidence: 79%

“…A final important characteristic of the far field is its temporal intermittency. Noise is observed to recur at St ≈ 0.2 in temporally localized bursts, a behavior that can be detected using time-local analysis (Cavalieri et al 2011a, Guj et al 2003, Hileman et al 2005, Juvé et al 1980 or characterized with a wavelet basis (Koenig et al 2012).…”

Section: Jet-noise Sensitivity To Upstream Conditionsmentioning

confidence: 99%

“…The traditional methods use monopole sources but can be extended to multipoles (see Suzuki 2010). When a wave-packet ansatz is used (Koenig et al 2012, Morris 2009, Papamoschou 2011, one can obtain parameters such as envelope amplitude, wavelength, position, and convection velocity using far-field measurements. Cavalieri et al (2012a) recently imposed radial structure on the wave-packet ansatz using eigenfunctions from linear stability analysis and used azimuthally decomposed far-field measurements to determine envelope parameters for higher-order azimuthal modes (m = 1 and m = 2).…”

Section: Jet-noise Sensitivity To Upstream Conditionsmentioning

confidence: 99%

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Wave Packets and Turbulent Jet Noise

Jordan

Colonius

2013

Annu. Rev. Fluid Mech.

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525

299

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Turbulent jet noise is a controversial fluid mechanical puzzle that has amused and bewildered researchers for more than half a century. Whereas numerical simulations are now capable of simultaneously predicting turbulence and its radiated sound, the theoretical framework that would guide noise-control efforts is incomplete. Wave packets are intermittent, advecting disturbances that are correlated over distances far exceeding the integral scales of turbulence. Their signatures are readily distinguished in vortical turbulence; the irrotational, evanescent near field; and the propagating far field. We review evidence of the existence, energetics, dynamics, and acoustic efficiency of wave packets. We highlight how extensive data available from simulations and modern measurement techniques can be used to distill acoustically relevant turbulent motions. The evidence supports theories that seek to represent wave packets as instability waves, or more general modal solutions of the governing equations, and confirms the acoustic importance of these structures in the aft-angle radiation of high subsonic and supersonic jets. The resulting unified view of wave packets provides insights that can help guide control strategies.

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Section: Intermittency: Loud and Quiet Flowsmentioning

confidence: 79%

Section: Jet-noise Sensitivity To Upstream Conditionsmentioning

confidence: 99%

Section: Jet-noise Sensitivity To Upstream Conditionsmentioning

confidence: 99%

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Wave Packets and Turbulent Jet Noise

Jordan

Colonius

2013

Annu. Rev. Fluid Mech.

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525

299

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“…Our idea is to permit these additional degrees of freedom by incorporating some low-frequency unsteadiness in the base flow. This low-frequency is suggested by the time-scale of the arrival of intermittent high-amplitude bursts of sound observed in farfield measurements (St ≈ 0.02 13 ), and by the slow time-scale used in the jittering wavepackets of Cavalieri et al 10 and which led to quantitatively accurate calculations of sound radiation.…”

Section: Introductionmentioning

confidence: 91%

Just enough jitter for jet noise?

Zhang

Jordan

Lehnasch

et al. 2014

20th AIAA/CEAS Aeroacoustics Conference

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We use model problems to explore the mechanisms that underpin jitter and coherence decay-related phenomena, both of which are important for wavepacket sound generation from subsonic jets. The inquiry is motivated by the incapacity of linear models to capture these important dynamic traits explicitly, and the need to understand how to distill a non-linear system down to some simplified form in which they are preserved.We first consider solutions of the non-linear Burgers' equation subject to periodic and stochastic upstream forcing; from these we obtain time-invariant and time-varying base flows about which linearisation is performed. The linearised systems are driven with upstream conditions similar to the non-linear case and the solutions analysed in terms of jitter and coherence decay; both can be preserved when linearisation is performed about a time-varying base flow.A similar investigation is then undertaken using the Linearised Euler Equations (LEE). Solutions are obtained using a previously studied, experimentally obtained, base flow, on which low-frequency, deterministic and stochastic, time variations are imposed. This introduction of time variations in the base flow amounts to a constrained permission of non-linear dynamics and additional, associated, degrees of freedom in what remains a linear model. The axial and radial hydrodynamic structures and radiated sound fields of the resulting wavepackets are compared with those obtained using a steady base flow. It is shown that many of the discrepancies observed between classical linear models (stability theory or LEE for instance) and experiment can be reduced: the wavepackets jitter, their axial coherence decays, the axial evolution of their fluctuation energy downstream of the end of the potential core shows qualitative agreement with experiment; and, most importantly, sound levels are boosted by many orders of magnitude.

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“…The same track was followed by Fleury et al 18 on a cylindrical Kirchhoff surface in the context of round jet noise. The acoustic energy radiated by a pressure distribution is triggered by its modes in the wavenumber spectrum lower than the acoustic wavenumber (supersonic phase speed 9,15,19,20 ). The localized spatial envelope yields an amplitude modulation in the wavenumber spectrum, instead of a single pic at the hydrodynamic wavenumber in the case of a wave without space modulation.…”

Section: Introductionmentioning

confidence: 99%

The influence of a pressure wavepacket's characteristics on its acoustic radiation

Serré

Robinet

Margnat

2015

The Journal of the Acoustical Society of America

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Noise generation by flows is modeled using a pressure wavepacket to excite the acoustic medium via a boundary condition of the homogeneous wave equation. The pressure wavepacket is a generic representation of the flow unsteadiness, and is characterized by a space envelope of pseudo-Gaussian shape and by a subsonic phase velocity. The space modulation yields energy in the supersonic range of the wavenumber spectrum, which is directly responsible for sound radiation and directivity. The influence of the envelope's shape on the noise emission is studied analytically and numerically, using an acoustic efficiency defined as the ratio of the acoustic power generated by the wavepacket to that involved in the modeled flow. The methodology is also extended to the case of acoustic propagation in a uniformly moving medium, broadening possibilities toward practical flows where organized structures play a major role, such as co-flow around cruising jet, cavity, and turbulent boundary layer flows. The results of the acoustic efficiency show significant sound pressure levels, especially for asymmetric wavepackets radiating in a moving medium.

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Farfield filtering and source imaging of subsonic jet noise

Cited by 48 publications

References 31 publications

Wave Packets and Turbulent Jet Noise

Wave Packets and Turbulent Jet Noise

Just enough jitter for jet noise?

The influence of a pressure wavepacket's characteristics on its acoustic radiation

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