Vortex dynamics and sound emission in excited high-speed jets

Crawley, Michael; Gefen, Lior; Kuo, Ching-Wen; Samimy, Mo; Camussi, Roberto

doi:10.1017/jfm.2017.906

Cited by 15 publications

(14 citation statements)

References 67 publications

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“…This is readily seen in irrotational near-field pressure spectra (Fig. 7) collected from an excited Mach 0.9 jet [107,165]. The high-amplitude nature of the LAFPA-produced perturbations ensures that at least one of the several harmonics has sufficient amplitude to excite natural instabilities.…”

Section: Actuatorsmentioning

confidence: 89%

“…Therefore, either multiple pairings must take place after the structure roll-up and before the end of potential core or the shear layer must grow sufficiently fast for f n θ to approach f p D. Consequently, the initial instability wave development and roll-up, and the potential pairing events, must occur (if at all) between the nozzle exit and the end of the potential core. The structures normally observed in experiments are those with passage frequency of f p , unless special effort is used to visualize the early part of the shear-layer development [107]. It has been shown experimentally that the pairing processes that take place in FSL [14,54] occur in jets as well and are responsible for decreasing the passage frequency of the LSS from the initial shear-layer value of St n f n θ 0 ∕U J ∼ 0.016 to the passage frequency at the end of the potential core, St p f p D∕U J ∼ 0.3 [25].…”

Section: A Shear Layer and Jet Column Modesmentioning

confidence: 99%

“…Further insight into the initial development of LSS in an excited jet is provided by the results of Crawley et al [107,165]. In this work, the development of axisymmetric ring vortices within the jet shear layer over the jet core region of a Mach 0.9 jet with a Reynolds number of 6.2 × 10 5 was investigated using time-resolved, near-field pressure measurements and simultaneously acquired synchronized non-time-resolved, instantaneous velocity measurements provided by streamwise planar PIV.…”

Section: B Development Of Large-scale Structures In Excited Jetsmentioning

confidence: 99%

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Excitation of Free Shear-Layer Instabilities for High-Speed Flow Control

2018

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Free shear layers are building blocks of many flows of interest in applications, including jets, cavity flows, and separated flows. It was found several decades ago that free shear layers are unstable to small perturbations over a wide range of frequencies, that they are dominated by coherent large-scale structures (even at high Reynolds numbers), and that the dynamics of these structures dominate important processes: entrainment, mixing, momentum transport, and noise generation. These findings motivated extensive research activities to actively control their development using excitation of instabilities, but early experimental research focused primarily on the control of low-speed, low-Reynolds-number free shear layers. This extensive body of the literature is briefly reviewed. The authors' recent work using localized arc filament plasma actuators in jets shows that free shear layers respond to the excitation over a large range of conditions that have been explored: jet Mach number (up to 1.65), convective Mach number (up to 1), and Reynolds number (up to 1.65 × 10 6). However, the nature of large-scale structures, shear-layer growth rate, and generation of Mach waves all depend on the jet Mach number and compressibility level. The results clearly demonstrate the similarity of instability processes and development of large-scale structures in free shear layers, regardless of the Mach or Reynolds numbers. Nomenclature

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Section: Actuatorsmentioning

confidence: 89%

Section: A Shear Layer and Jet Column Modesmentioning

confidence: 99%

Section: B Development Of Large-scale Structures In Excited Jetsmentioning

confidence: 99%

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Excitation of Free Shear-Layer Instabilities for High-Speed Flow Control

2018

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“…Perhaps the most promising frequency-domain active control is the use of plasma actuators, the most successful example of which is arguably the Localized Arc-Filament Plasma Actuators developed at the Ohio State University. [141][142][143][144][145][146][147] These actuators are capable of forcing the flow across a range of frequencies and azimuthal modes. There have been some other novel attempts at forcing the jet away from its natural frequency using spinning valves and plugs, 148,149 though this technology is still in its relative infancy.…”

Section: Active Flow Controlmentioning

confidence: 99%

Aeroacoustic resonance and self-excitation in screeching and impinging supersonic jets – A review

Edgington-Mitchell

2019

International Journal of Aeroacoustics

172

104

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Supersonic jets, particularly shock-containing jets, often exhibit high-intensity, discrete-frequency acoustic tones. These tones are the signature of an aeroacoustic resonance loop established by the flow. This paper considers two of the classical forms of supersonic jet resonance: screech in shock-containing free jets and tones generated by the impingement of a jet against a surface. The first half of the paper provides a historical perspective on research into both forms of resonance, ranging from the seminal works of Alan Powell to recent contributions from high-fidelity numerical simulation, experiment, and stability theory. The second half of the paper provides a critical assessment of current understanding around the four processes that characterize jet resonance: a downstream propagation of energy, an acoustic generation mechanism, an upstream propagation of energy, and a receptivity mechanism.

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“…Our focus will be on the progress made in developing an integrated approach, in which nonlinear evolution of instability modes as a physical entity, and their acoustic radiation are both described on the basis of first principles. Experiments reveal that noise is emitted primarily as the wavepackets undergo growth and attenuation [36][37][38]. The emission is significantly enhanced by the jittering or intermittency of the wavepackets.…”

Section: Acoustic Radiation Of Instability Waves In Free Shear Flowsmentioning

confidence: 99%

First-principle description of acoustic radiation of shear flows

Zhang

2019

Phil. Trans. R. Soc. A.

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As a methodology complementary to acoustic analogy, the asymptotic approach to aeroacoustics seeks to predict aerodynamical noise on the basis of first principles by probing into the physical processes of acoustic radiation. The present paper highlights the principal ideas and recent developments of this approach, which have shed light on some of the fundamental issues in sound generation in shear flows. The theoretical work on sound wave emission by nonlinearly modulated wavepackets of supersonic and subsonic instability modes in free shear flows identifies the respective physical sources or emitters. A wavepacket of supersonic modes is itself an efficient emitter, radiating directly intensive sound in the form of a Mach wave beam, the frequencies of which are in the same band as those of the modes in the packet. By contrast, a wavepacket of subsonic modes radiates very weak sound directly. However, the nonlinear self-interaction of such a wavepacket generates a slowly modulated mean-flow distortion, which then emits sound waves with low frequencies and long wavelengths on the scale of the wavepacket envelope. In both cases, the acoustic waves emitted to the far field are explicitly expressed in terms of the amplitude function of the wavepacket. The asymptotic approach has also been applied to analyse generation of sound waves in wall-bounded shear flows on the triple-deck scale. Several subtleties have been found. The near-field approximation has to be worked out to a sufficiently higher order in order just to calculate the far-field sound at leading order. The back action of the radiated sound on the flow in the viscous sublayer and the main shear layer is accounted for by an impedance coefficient. This effect is of higher order in the subsonic regime, but becomes a leading order in the transonic and supersonic regimes. This article is part of the theme issue ‘Frontiers of aeroacoustics research: theory, computation and experiment’.

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Vortex dynamics and sound emission in excited high-speed jets

Cited by 15 publications

References 67 publications

Excitation of Free Shear-Layer Instabilities for High-Speed Flow Control

Excitation of Free Shear-Layer Instabilities for High-Speed Flow Control

Aeroacoustic resonance and self-excitation in screeching and impinging supersonic jets – A review

First-principle description of acoustic radiation of shear flows

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