Characteristics of acoustic and hydrodynamic waves in under-expanded supersonic impinging jets

Karami, Shahram; Edgington-Mitchell, Daniel; Theofilis, Vassilios; Soria, Julio

doi:10.1017/jfm.2020.740

Cited by 20 publications

(6 citation statements)

References 111 publications

(250 reference statements)

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“…The assumption of laminar inlet flow is considered to be valid as the nozzle of the under-expanded supersonic jet has a high contraction ratio similar to previous experimental studies ( Edgington-Mitchell, Honnery & Soria 2014;Amili et al 2015a,b;Soria & Amili 2015); hence, the inlet turbulence is considered to be negligible. The Reynolds number based on inlet velocity and jet diameter is 50 000, which is similar to our previous studies (Karami et al 2018a(Karami et al , 2020aSikroria et al 2020), to maintain the LES resolution requirement under acceptable computational cost (Kawai & Lele 2010). Region…”

Section: Configurations and Numerical Methodssupporting

confidence: 71%

Influence of nozzle external geometry on wavepackets in under-expanded supersonic impinging jets

Karami

Soria

2021

J. Fluid Mech.

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In this study, large-eddy simulations are utilised to unravel the influence of the nozzle's external geometry on upstream-travelling waves in under-expanded supersonic impinging jets. Three configurations, a thin-lipped, a thin-lipped with a sponge and an infinite-lipped nozzle are considered with the other non-dimensionalised geometrical and flow variables identical for the three cases. Spectral proper orthogonal decomposition is applied to the Mack norm, i.e. the energy norm based on the stagnation energy, to obtain the spatial modes at their corresponding frequency. The spectral decomposition of the spatial modes at optimal and suboptimal frequencies is used to isolate the wavepackets into upstream- and downstream-propagating waves based on their phase velocity. It is found that the external geometry of the nozzle has a significant influence on the first-order statistics even though the governing non-dimensional parameters are the same for all three cases. Multiple peaks emerge in the energy spectra at distinct frequencies corresponding to axisymmetric azimuthal modes for each case. The downstream-propagating wavepackets have a high amplitude at the shear layer of the three jets with the mode shapes resembling Kelvin–Helmholtz instability waves, while the upstream-travelling wavepackets exist in the three regions of the near field, shear layer and inside of the jet. The barrel shock at the nozzle exit appears as a flexible shield, which prevents upstream-travelling waves from reaching the internal region of the nozzle, where the upstream-travelling waves travel obliquely with one side of the wavefront is crawling on the reflected shock while the other side is guided by the shear layer. These latter waves can reach the nozzle lip via inside of the jet. The spectral decomposition of the spatial modes at optimal and suboptimal frequencies show that all three forms of the near field, shear layer and inside jet upstream-travelling wavepackets contribute to the receptivity process while their contributions and strength are altered by the change of the external geometry of the nozzle.

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Section: Configurations and Numerical Methodssupporting

confidence: 71%

Influence of nozzle external geometry on wavepackets in under-expanded supersonic impinging jets

Karami

Soria

2021

J. Fluid Mech.

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“…Then the most unstable frequencies decrease with the axial distance due to the shear-layer thickening. 56,58 They are reduced down to St = 0.5 at z = 2r 0 and they reach Strouhal numbers lower than 0.2 near the plate. Therefore, at high frequencies, the instability waves grow over a very short distance to the nozzle exit whereas at low frequencies, they are amplified all over the nozzle-to-plate distance.…”

Section: Shear-layer Velocity Spectramentioning

confidence: 98%

Acoustic tones generated by impinging jets: Differences between laminar and highly-disturbed nozzle-exit boundary layers

Varé,

Bogey

2024

International Journal of Aeroacoustics

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The differences between the acoustic tones generated by impinging jets with laminar and highly-disturbed nozzle-exit boundary layers are investigated. For that, jets at Mach numbers between 0.6 and 1.3 impinging on a flat plate at a distance of 8 nozzle radii from the nozzle exit are computed using large-eddy simulations. The amplitudes of the tones generated by the jets through feedback loops establishing between the nozzle and the plate are found to be significantly affected by the exit turbulent disturbances. In the present study, overall, they are lower for the initially laminar jets than for the initially disturbed ones. The level decrease varies from a few dB up to 15 dB, depending on the tones, which can change the frequencies of the dominant tones and the numbers and azimuthal structures of their associated feedback modes. For Mach numbers 0.75 and 0.8, for instance, the dominant tone frequencies are approximately two times lower for the initially laminar jets than for the other ones, yielding a better agreement with experiments of the literature in the former case. For a Mach number of 1.1, as a second example, the dominant tone is associated with the axisymmetric third feedback mode in the laminar case but with the helical fifth feedback mode in the disturbed case. The differences in the tone amplitude are finally discussed by estimating the power gains of the shear-layer instability waves between the nozzle and the plate using linear stability analysis for the axisymmetric mode. In most cases, at the frequency of a specific tone, the higher the gain, the stronger the acoustic tone.

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“…They are confined in the jets when the jets are subsonic, but lie outside when the jets are supersonic and are characterized by a negative group velocity. In order to check whether these waves called neutral sound waves are occurring in the present configuration, the characteristics of the wavepackets at the jet shear layer can be analyzed as proposed by Karami et al [43] whose used this approach to identify neutral waves in supersonic under-expanded impinging jets. To do so, a spatio-temporal decomposition of the time history of pressure at the jet shear-layer has been performed and is shown in Fig.…”

Section: Jetl55-90d Casementioning

confidence: 99%

Spectral proper orthogonal decomposition of coupled hydrodynamic and acoustic fields: Application to impinging jet configurations (draft)

Fiore¹,

Parisot-Dupuis²,

Etchebarne³

et al. 2022

Computers & Fluids

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Characteristics of acoustic and hydrodynamic waves in under-expanded supersonic impinging jets

Abstract: Abstract

Cited by 20 publications

References 111 publications

Influence of nozzle external geometry on wavepackets in under-expanded supersonic impinging jets

Influence of nozzle external geometry on wavepackets in under-expanded supersonic impinging jets

Acoustic tones generated by impinging jets: Differences between laminar and highly-disturbed nozzle-exit boundary layers

Spectral proper orthogonal decomposition of coupled hydrodynamic and acoustic fields: Application to impinging jet configurations (draft)

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