Jittering wave-packet models for subsonic jet noise

Cavalieri, André V. G.; Jordan, Peter; Agarwal, Anurag; Gervais, Yves

doi:10.1016/j.jsv.2011.04.007

Cited by 168 publications

(81 citation statements)

References 42 publications

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“…The spatio-temporal modulations of this wavepacket are known to be central to the genesis of downstream propagated noise. Cavalieri et al (2011) induced temporal modulations in the amplitude and spatial extent ('jittering') of a model wavepacket to obtain a good match with sound levels predicted by LES in subsonic jets. Semeraro, Lesshafft & Sandberg (2015) optimally forced a linear wavepacket model in a subsonic jet at St = 0.6 to recreate downstream-direction response and compared it with the Fourier modes obtained from direct numerical simulation.…”

Section: Core Dynamics Of the Acoustic Modementioning

confidence: 94%

Acoustic, hydrodynamic and thermal modes in a supersonic cold jet

Nair

Gaitonde

2016

J. Fluid Mech.

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Large-eddy simulation data for a Mach 1.3 round jet are decomposed into acoustic, hydrodynamic and thermal components using Doak's momentum potential theory. The decomposed fields are then analysed to examine the properties of each mode and their dynamics based on the transport equation for the total fluctuating enthalpy. The solenoidal fluctuations highlight hydrodynamic components of the jet and capture the shear layer growth and breakdown process. The acoustic mode exhibits a jittering coherent wavepacket structure in the turbulent region and consequent highly directional downstream radiation. The expected radial decay rates, r for acoustic, are recovered and closely follow the universal radiation spectra in the sideline and downstream directions. The scalogram of the acoustic mode in the near-acoustic-field region is consistent with that of the pressure perturbation signal in the acoustic-frequency range, but effectively removes the hydrodynamic and thermal content. The time-resolved and mean behaviour of terms in the total fluctuating enthalpy equation is analysed in detail. A large-scale intermittent event in the near-acoustic field is shown to be associated with an intrusion of vortices from the shear layer into the core of the jet. Acoustic sources are created when the resulting negative fluctuations in the solenoidal component interact with positive fluctuations in the Coriolis acceleration term. The latter are associated with regions of high vorticity on the inner side of the shear layer. In contrast, sinks result from the interaction of solenoidal momentum fluctuations with positive entropy gradients along entrainment streaks.

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Section: Core Dynamics Of the Acoustic Modementioning

confidence: 94%

Acoustic, hydrodynamic and thermal modes in a supersonic cold jet

Nair

Gaitonde

2016

J. Fluid Mech.

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“…These streaks contain noticeable helical structures. Cavalieri et al (2011b) Resolution (%) FIGURE 9. Percentage resolution of linearly correlated noise by OID and POD modes, accumulated over the number N of used modes.…”

Section: Acoustically Optimized Oid Of Jet Flowmentioning

confidence: 99%

On least-order flow representations for aerodynamics and aeroacoustics

et al. 2012

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We propose a generalization of proper orthogonal decomposition (POD) for optimal flow resolution of linearly related observables. This Galerkin expansion, termed 'observable inferred decomposition' (OID), addresses a need in aerodynamic and aeroacoustic applications by identifying the modes contributing most to these observables. Thus, OID constitutes a building block for physical understanding, leastbiased conditional sampling, state estimation and control design. From a continuum of OID versions, two variants are tailored for purposes of observer and control design, respectively. Firstly, the most probable flow state consistent with the observable is constructed by a 'least-residual' variant. This version constitutes a simple, easily generalizable reconstruction of the most probable hydrodynamic state to preprocess efficient observer design. Secondly, the 'least-energetic' variant identifies modes with the largest gain for the observable. This version is a building block for Lyapunov control design. The efficient dimension reduction of OID as compared to POD is demonstrated for several shear flows. In particular, three aerodynamic and aeroacoustic goal functionals are studied: (i) lift and drag fluctuation of a two-dimensional cylinder wake flow; (ii) aeroacoustic density fluctuations measured by a sensor array and emitted from a two-dimensional compressible mixing layer; † Email address for correspondence: michael.schlegel@tu-berlin.de

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“…For low acoustic angles, consideration of azimuthal mode m and frequency ω of the T xx component of Lighthill's stress tensor leads to where k a is the acoustic wavenumber ω/c. The Bessel function of the first kind, J m , results from azimuthal integration, and leads to a lower efficiency of high azimuthal modes, as explored previously in the literature (Michalke 1970;Michalke & Fuchs 1975;Mankbadi & Liu 1984;Cavalieri et al 2011). This effect is illustrated in figure 9.…”

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confidence: 96%

Wavepackets in the velocity field of turbulent jets

et al. 2013

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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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Jittering wave-packet models for subsonic jet noise

Cited by 168 publications

References 42 publications

Acoustic, hydrodynamic and thermal modes in a supersonic cold jet

Acoustic, hydrodynamic and thermal modes in a supersonic cold jet

On least-order flow representations for aerodynamics and aeroacoustics

Wavepackets in the velocity field of turbulent jets

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