Variation of shock-spacing during screech stage-jumps

Clem, Michelle M.; Zaman, K. B. M. Q.; Fagan, A. L.

doi:10.1177/1475472x16630888

Cited by 5 publications

(3 citation statements)

References 30 publications

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“…uncertainties are insignificant in comparison to the margin of error pointed out on k s . The modulation wavenumber is found to be larger than the shock cell wavenumber by a few per cent, except for the case M j = 1.15 that exhibits k sw 28 % larger than k sc because of the jump in frequency, whereas no change in aerodynamic characteristics of the jet is observed (Clem, Zaman & Fagan 2016). The second largest k − sw in comparison to k sc is found for case M j = 1.13: k − sw is 10 % larger than k sc .…”

Section: Wavenumber-frequency Spectrum Analysismentioning

confidence: 72%

Experimental characterisation of the screech feedback loop in underexpanded round jets

2017

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Near-field acoustic measurements and time-resolved schlieren visualisations are performed on 10 round jets with the aim of analysing the different parts of the feedback loop related to the screech phenomenon in a systematic fashion. The ideally expanded Mach number of the studied jets ranges from $M_{j}=1.07$ to $M_{j}=1.50$. The single source of screech acoustic waves is found at the fourth shock tip for A1 and A2 modes, and at either the third or the fourth shock tip for the B mode, depending on the Mach number. The phase of the screech cycle is measured throughout schlieren visualisations in the shear layer from the nozzle to the source. Estimates of the convective velocities are deduced for each case, and a trend for the convective velocity to grow with the axial distance is pointed out. These results are used together with source localisation deduced from a two-microphone survey to determine the number of screech periods contained in a screech loop. For the A1 and B modes, four periods are contained in a loop for cases in which the radiating shock is the fourth, and three periods when the radiating shock tip is the third, whereas the loop of the A2 mode contains five periods.

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Section: Wavenumber-frequency Spectrum Analysismentioning

confidence: 72%

Experimental characterisation of the screech feedback loop in underexpanded round jets

2017

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“…However, in Tam et al (1986) and the body of work that followed, it was typically assumed that higher-order shock cell modes could be neglected, thus returning to an equivalence in the application of the two models. Equation (1.1) can produce accurate predictions of screech frequency for some jet operating conditions; however, it is unable to account for the modal staging behaviour of jet screech, as neither the convection velocity nor the shock spacing has been observed to change in a discontinuous manner with changes in operating condition (Clem, Zaman & Fagan 2016;Mercier, Castelain & Bailly 2017).…”

Section: Introductionmentioning

confidence: 99%

“…Equation can produce accurate predictions of screech frequency for some jet operating conditions; however, it is unable to account for the modal staging behaviour of jet screech, as neither the convection velocity nor the shock spacing has been observed to change in a discontinuous manner with changes in operating condition (Clem, Zaman & Fagan 2016; Mercier, Castelain & Bailly 2017).…”

Section: Introductionmentioning

confidence: 99%

A unifying theory of jet screech

Edgington-Mitchell

Liu

et al. 2022

J. Fluid Mech.

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This paper describes the mechanism underpinning modal staging behaviour in screeching jets. An upstream-propagating subsonic guided-jet mode is shown to be active in all stages of screech. Axial variation of shock-cell spacing manifests in the spectral domain as a series of suboptimal peaks. It is demonstrated that the guided-jet mode may be energized by interactions of the Kelvin–Helmholtz wavepacket with not only the primary shock wavenumber peak, but also suboptimal peaks; interaction with suboptimals is shown to be responsible for closing the resonance loop in multiple stages of jet screech. A consideration of the full spectral representation of the shocks reconciles several of the classical models and results for jet screech that had heretofore been paradoxical. It is demonstrated that there are multiple standing waves present in the near field of screeching jets, corresponding to the superposition of the various waves active in these jets. Multimodal behaviour is explored for jets in a range of conditions, demonstrating that multiple peaks in the frequency spectra can be due to either changes in which peak of the shock spectra the Kelvin–Helmholtz wavepacket is interacting with, or a change in azimuthal mode, or both. The absence of modal staging in high-aspect-ratio non-axisymmetric jets is also explained in the context of the aforementioned mechanism. The paper closes with a new proposed theory for frequency selection in screeching jets, based on the observation that these triadic interactions appear to underpin selection of the guided-jet mode wavelength in all measured cases.

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The source localization and dynamical evolution of axisymmetric screech modes in underexpanded supersonic jets

Luo

Han

et al. 2023

Aerospace Science and Technology

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Variation of shock-spacing during screech stage-jumps

Cited by 5 publications

References 30 publications

Experimental characterisation of the screech feedback loop in underexpanded round jets

Experimental characterisation of the screech feedback loop in underexpanded round jets

A unifying theory of jet screech

The source localization and dynamical evolution of axisymmetric screech modes in underexpanded supersonic jets

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