Near-field Wavepackets and the Far-field Sound of a Subsonic Jet

Breakey, David E. S.; Jordan, Peter; Cavalieri, André V. G.; Léon, Olivier

doi:10.2514/6.2013-2083

Cited by 43 publications

(45 citation statements)

References 25 publications

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“…The use of an axial POD is not feasible with the present experimental setup, since separate measurements were taken for each value of x/D. Moreover, preliminary comparisons of the measured near-field pressure of the present jets with linear PSE led to good agreement up to x/D = 8.9, which is well beyond the end of the potential core (Breakey et al 2013).…”

Section: Axial Development Of Wavepacketsmentioning

confidence: 93%

Wavepackets in the velocity field of turbulent jets

Cavalieri

Rodríguez

Jordan

et al. 2012

18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)

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173

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We study the velocity fields of unforced, high Reynolds number, subsonic jets, issuing from round nozzles with turbulent boundary layers. The objective of the study is to educe wavepackets in such flows and to explore their relationship with the radiated sound. The velocity field is measured using a hot-wire anemometer and a stereoscopic, time-resolved PIV system. The field can be decomposed into frequency and azimuthal Fourier modes. The low-angle sound radiation is measured synchronously with a microphone ring array. Consistent with previous observations, the azimuthal wavenumber spectra of the velocity and acoustic pressure fields are distinct. The velocity spectrum of the initial mixing layer exhibits a peak at azimuthal wavenumbers m ranging from 4 to 11, and the peak is found to scale with the local momentum thickness of the mixing layer. The acoustic pressure field is, on the other hand, predominantly axisymmetric, suggesting an increased relative acoustic efficiency of the axisymmetric mode of the velocity field, a characteristic that can be shown theoretically to be caused by the radial compactness of the sound source. This is confirmed by significant correlations, as high as 10 %, between the axisymmetric modes of the velocity and acoustic pressure fields, these values being significantly higher than those reported for two-point flow-acoustic correlations in subsonic jets. The axisymmetric and first helical modes of the velocity field are then compared with solutions of linear parabolized stability equations (PSE) to ascertain if these modes correspond to linear wavepackets. For all but the lowest frequencies close agreement is obtained for the spatial amplification, up to the end of the potential core. The radial shapes of the linear PSE solutions also agree with the experimental results over the same region. The results suggests that, despite the broadband character of the turbulence, the evolution of Strouhal numbers 0.3 St 0.9 and azimuthal modes 0 and 1 can be modelled as linear wavepackets, and these are associated with the sound radiated to low polar angles.

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Section: Axial Development Of Wavepacketsmentioning

confidence: 93%

Wavepackets in the velocity field of turbulent jets

Cavalieri

Rodríguez

Jordan

et al. 2012

18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)

Self Cite

173

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“…Only limited growth-rate results will therefore be presented in what follows, and these should be treated with caution, bearing in mind what we have said here. Phase velocities, on the other hand, are predicted with good accuracy over the entire spectrum of relevant frequencies (Gudmundsson & Colonius 2011;Breakey et al 2013). More solid conclusions that can thus be drawn when considering this wavepacket parameter, on which, as mentioned above, the sound field exhibits exponential dependence.…”

Section: Analysis and Interpretationmentioning

confidence: 99%

Jet-noise control by fluidic injection from a rotating plug: linear and nonlinear sound-source mechanisms

et al. 2016

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We present a study of the turbulent and acoustic fields of subsonic jets, controlled by means of a novel actuator that introduces perturbations via steady-fluidic actuation from a rotating centrebody. The actuation can produce louder or quieter jets, and these are analysed using time-resolved stereoscopic particle image velocimetry and a hot-wire anemometer. We place the analysis in the framework of wavepackets and linear stability theory, whence we show, using solutions of the linear parabolised stability equations, that the quieter flows can be understood to result from a mean-flow deformation that modifies wavepacket dynamics, and in particular their phase velocities, which are significantly reduced. The mean-flow deformation is shown, by a triple decomposition, to be due to the generation of Reynolds stresses associated with incoherent turbulence (rather than coherent structures) which arises when the actuation energises the flow with a frequency-azimuthal wavenumber (ω-m) combination to which the mean flow is stable. When the actuation excites the flow with an ω-m combination to which the mean flow is unstable, the response is dominated by coherent structures, whose rapid growth takes them beyond the linear limit, where they undergo quadratic wave interactions and lead, consequently, to a louder flow.

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“…Thus, the intermittency of the wavepackets (which broadens the wavenumber spectrum) has relatively little contribution to the peak acoustic radiation in the isothermal supersonic jet. In contrast, in the case of a subsonic (Mach 0.9) jet, Cavalieri et al (2011) used a different procedure to model the average wavepacket, and found it to under-predict the far-field PSD by 25 dB/St at the peak radiation aft angle (see also Baqui et al (2013) and Breakey et al (2013)). However, agreement was much improved when the intermittency of the wavepackets was modelled empirically by these authors, as well as by Reba, Narayanan & Colonius (2010) earlier.…”

Section: Comparisons Of the Acoustic Fieldmentioning

confidence: 99%

Wavepacket models for supersonic jet noise

et al. 2014

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Gudmundsson and Colonius (J. Fluid Mech., vol. 689, 2011, pp. 97-128) have recently shown that the average evolution of low-frequency, low-azimuthal modal large-scale structures in the near field of subsonic jets are remarkably well predicted as linear instability waves of the turbulent mean flow using parabolized stability equations. In this work, we extend this modelling technique to an isothermal and a moderately heated Mach 1.5 jet for which the mean flow fields are obtained from a high-fidelity large-eddy simulation database. The latter affords a rigourous and extensive validation of the model, which had only been pursued earlier with more limited experimental data. A filter based on proper orthogonal decomposition is applied to the data to extract the most energetic coherent components. These components display a distinct wavepacket character, and agree fairly well with the parabolized stability equations model predictions in terms of near-field pressure and flow velocity. We next apply a Kirchhoff surface acoustic propagation technique to the near-field pressure model and obtain an encouraging match for far-field noise levels in the peak aft direction. The results suggest that linear wavepackets in the turbulence are responsible for the loudest portion of the supersonic jet acoustic field.

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Near-field Wavepackets and the Far-field Sound of a Subsonic Jet

Cited by 43 publications

References 25 publications

Wavepackets in the velocity field of turbulent jets

Wavepackets in the velocity field of turbulent jets

Jet-noise control by fluidic injection from a rotating plug: linear and nonlinear sound-source mechanisms

Wavepacket models for supersonic jet noise

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