The generation of screech tones by shock leakage

Edgington-Mitchell, Daniel; Weightman, Joel L.; Lock, Samuel; Kirby, Rhiannon; Nair, Vineeth; Soria, Julio; Honnery, Damon

doi:10.1017/jfm.2020.945

Cited by 29 publications

(21 citation statements)

References 70 publications

(154 reference statements)

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“…The model managed to reproduce characteristics of screech observed in experiments (Shariff & Manning 2013; Edgington-Mitchell et al. 2021 b ), even with strong simplifications of its underlying assumptions.…”

Section: Introductionmentioning

confidence: 97%

Absolute instability in shock-containing jets

et al. 2021

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We present an analysis of the linear stability characteristics of shock-containing jets. The flow is linearised around a spatially periodic mean, which acts as a surrogate for a mean flow with a shock-cell structure, leading to a set of partial differential equations with periodic coefficients in space. Disturbances are written using the Floquet ansatz and Fourier modes in the streamwise direction, leading to an eigenvalue problem for the Floquet exponent. The characteristics of the solution are directly compared with the locally parallel case, and some of the features are similar. The inclusion of periodicity induces minor changes in the growth rate and phase velocity of the relevant modes for small shock amplitudes. On the other hand, the eigenfunctions are now subject to modulation related to the periodicity of the flow. Analysis of the spatio-temporal growth rates led to the identification of a saddle point between the Kelvin–Helmholtz mode and the guided jet mode, characterising an absolute instability mechanism. Frequencies and mode shapes related to the saddle points for two conditions (associated with axisymmetric and helical modes) are compared with screech frequencies and the most energetic coherent structures of screeching jets, resulting in a good agreement for both. The analysis shows that a periodic shock-cell structure has an impulse response that grows upstream, leading to oscillator behaviour. The results suggest that screech can occur in the absence of a nozzle, and that the upstream reflection condition is not essential for screech frequency selection. Connections to previous models are also discussed.

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Section: Introductionmentioning

confidence: 97%

Absolute instability in shock-containing jets

et al. 2021

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“…Whilst sound emissions from multiple sources have been experimentally observed (see e.g. Edgington-Mitchell et al 2021b), this mechanism can in principle be directive without requiring a streamwise distribution of sources. It remains to be established whether the directive sound beam associated with BBSAN and screech is due to the phased-array (Mach-wave) source effect, or the shock-leakage mechanism or both.…”

Section: Introductionmentioning

confidence: 99%

A complex-valued resonance model for axisymmetric screech tones in supersonic jets

et al. 2021

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We model the resonance mechanism underpinning generation of A1 and A2 screech tones in an under-expanded supersonic jet. Starting from the resonance model recently proposed by Mancinelli et al. (Exp. Fluids, vol. 60, 2019, p. 22), where the upstream-travelling wave is a neutrally stable guided-jet mode, we here present a more complete linear-stability-based model for screech prediction. We study temperature and shear-layer thickness effects and show that, in order to accurately describe the experimental data, the effect of the finite thickness of the shear layer must be incorporated in the jet-dynamics model. We then present an improved resonance model for screech-frequency predictions in which both downstream- and upstream-travelling waves may have a complex wavenumber and frequency. This resonance model requires knowledge of the reflection coefficients at the upstream and downstream locations of the resonance loop. We explore the effect of the reflection coefficients on the resonance model and propose an approach for their identification. The complex-mode model identifies limited regions of frequency–flow parameter space for which the resonance loop is amplified in time, a necessary condition for the resonance to be sustained. This model provides an improved description of the experimental measurements.

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“…A part of the shock leaks out of the flow, which creates a circular sound wave visible around z % 13.5r 0 and r 0 r 3r 0 . This sound generation mechanism, also involved in the production of screech noise [45][46][47], is referred to as shock leakage. It is shown here to be an efficient acoustic source in high-supersonic impinging jets in certain cases, as suggested by previous works [18,41].…”

Section: Sound Generation Near the Platementioning

confidence: 99%

Presence and properties of acoustic peaks near the nozzle of impinging rocket jets

Varé

Bogey

2022

Acta Acust.

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The presence and properties of acoustic peaks near the nozzle of impinging rocket jets have been investigated. Four jets at a Mach number of 3.1 impinging on a plate at a distance L = 15r0, 20r0, 25r0 and 30r0 from the nozzle, where r0 is the nozzle radius, have been computed using large-eddy simulations. In all cases, upstream-travelling pressure waves are generated by the jet impingement on the plate, with amplitudes decreasing with the nozzle-to-plate distance. The near-nozzle pressure spectra contain peaks, at frequencies not varying much with this distance. For L ≥ 20r0, the spectra are dominated by a low-frequency peak, whereas two additional high-frequency peaks emerge for L = 15r0. The low-frequency peak is associated with the azimuthal mode nθ = 0, whereas the two other ones are due to strong components for modes nθ ≥ 1. As for near-nozzle tones for free and impinging jets at lower Mach numbers, the peak frequencies fall close to the frequency bands of the upstream-propagating guided jet waves, showing a link between the peaks and the latter waves. Regarding the peak levels, they do not change significantly with the nozzle-to-plate distance for the low-frequency peak, but they decrease by 1.5 to 18 dB as the distance increases for the other peaks. Finally, for L ≥ 20r0, the near-nozzle peak frequency is close to that of the strongest shear-layer structures, indicating a connexion between the upstream noise and these structures. For L = 15r0, a shock-leakage mechanism of a near-plate shock is found to generate the upstream noise.

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The generation of screech tones by shock leakage

Abstract: Abstract

Cited by 29 publications

References 70 publications

Absolute instability in shock-containing jets

Absolute instability in shock-containing jets

A complex-valued resonance model for axisymmetric screech tones in supersonic jets

Presence and properties of acoustic peaks near the nozzle of impinging rocket jets

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