Intermittent modal coupling in screeching underexpanded circular twin jets

Bell, Graham; Cluts, Jordan D.; Samimy, Mo; Soria, Julio; Edgington-Mitchell, Daniel

doi:10.1017/jfm.2020.909

Cited by 18 publications

(23 citation statements)

References 61 publications

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“…Nevertheless, modelling screech intermittency may not be very straightforward. For example, recent studies of intermittent screech tones generated by under-expanded twin round jets [58] suggested that this erratic behavior of screech tones were attributed to a competition between two global modes of the flow system, which are a function of the inter-nozzle spacing and NPR.…”

Section: Discussionmentioning

confidence: 99%

Aeroacoustics of Twin Rectangular Jets Including Screech: Large-eddy Simulations with Experimental Validation

Jeun,

Karnam,

et al. 2021

Preprint

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High-fidelity large-eddy simulations (LES) are performed to investigate aeroacoustic characteristics of jets issuing from twin rectangular nozzles with an aspect ratio of 2:1 at two over-expanded conditions and the design condition. For all three jet conditions simulated, LES predicts qualitatively similar near-field flow statistics to those measured at the University of Cincinnati. Using the Ffowcs Williams-Hawkings method, LES captures the fundamental screech tone and its harmonics fairly well at multiple observer locations in the far-field. Intense jet flapping motions in the near-field along the minor axis, which are enhanced by jetto-jet interactions, are found to correspond to those frequencies. Moreover, the overall sound pressure levels are within 1-2 dB difference from the experimental measurements. However, the screech tones appear to be intermittent, as the twin-jet interaction pattern varies irregularly. To extract dominant flow structures at the screech frequencies and identify the twin-jet coupling modes, spectral proper orthogonal decomposition (SPOD) analysis is used. SPOD analysis recovers energetic peaks at the screech frequencies, and the corresponding leading modes indicate strong upstream radiation originating from the fifth/sixth shock-cells. For the two over-expanded conditions, the leading modes show anti-symmetric coupling in the minor axis at the fundamental screech frequencies. In contrast, the two jets behave symmetrically with respect to each other in the major axis, in line with the absence of jet flapping in this direction. Furthermore, the leading SPOD eigenvalues turn out to be, at least, two orders of magnitude larger than higher-order eigenvalues, suggesting potential of reduced-order models for the twin-jet screech.

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Section: Discussionmentioning

confidence: 99%

Aeroacoustics of Twin Rectangular Jets Including Screech: Large-eddy Simulations with Experimental Validation

Jeun,

Karnam,

et al. 2021

Preprint

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“…At specific nozzle spacings and Mach numbers, the coupling behaviour can become erratic, leading to periods where the jet can switch between symmetric or antisymmetric modes or uncouple entirely (Bell et al. 2021). This has been suggested to be the result of a competition between global modes of the flow, which is supported by the fact that different coupling symmetries exhibit similar growth rates and wavenumbers for the Kelvin–Helmholtz instability (Nogueira & Edgington-Mitchell 2021).…”

Section: Introductionmentioning

confidence: 99%

“…The aforementioned study by Bell et al. (2021) on twin round jets used modal decomposition of particle image velocimetry (PIV) data alongside time-frequency analysis of acoustic data to demonstrate that at some operating conditions the coupling between jets was steady, and at other conditions was highly intermittent. In rectangular twin jets intermittency has been observed both experimentally (Ghassemi Isfahani, Webb & Samimy 2021 b ) and numerically (Jeun, Wu & Lele 2021 a ; Jeun et al.…”

Section: Introductionmentioning

confidence: 99%

“…In Bell et al. (2021) similar round nozzles were studied in two facilities; while both facilities produced identifiable regions of steady and unsteady coupling, the transitions between these regions occurred at different NPR values. The results of any study of resonant coupling between twin jets will thus be specific to the boundary conditions of the simulation or experiment in question.…”

Section: Introductionmentioning

confidence: 99%

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Steady and unsteady coupling in twin weakly underexpanded round jets

Wong,

Stavropoulos,

Beekman

et al. 2023

J. Fluid Mech.

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We investigate the intermittency of the coupling behaviour in screeching twin round supersonic jets at low Mach numbers across a range of nozzle spacings. Application of proper orthogonal decomposition combined with time-frequency wavelet analysis and spectral proper orthogonal decomposition shows that intermittency can manifest in twin jets as either a competition between the two symmetries, or the jets uncoupling and recoupling. The time scales on which symmetry switching occurs can vary strongly, ranging from $O(10^2)$ to $O(10^3)$ screech cycles. A transition from one symmetry to another is accompanied by a slight change in the screech frequency ranging from 0.30 % to 0.63 %. It was observed that complete uncoupling occurred only at the largest nozzle spacing of $s/D=6$ and at Mach numbers close to modal staging. When the jets are uncoupled they screech at slightly different frequencies, with a disparity of approximately 0.6 %. The coupling is particularly intermittent in the transition from the A1 to A2 branch, where the A2 mode is first observed, and tends toward steady coupling with increasing Mach number.

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“…In the last 5 years, twin jets screech is still a research field. Coupling modes are investigated experimentally by Kuo [16], Knast [17] or Bell [18]. On this topic, numerical simulations of previous studies start to arise (Goparaju [19] on Kuo's setup [16], Gao [20] or Anh [21] on Walker's setup [10]).…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation of the Noise Radiated by Free Hot Supersonic Twin Jets

Troyes

Vincent

2022

28th AIAA/CEAS Aeroacoustics 2022 Conference

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Numerical simulation of the noise radiated by free hot supersonic twin jets is conducted by combining different numerical tools. These are based on the one hand on a high fidelity LES (Large Eddy Simulation) computation with geometric triggering of the turbulence in the nozzle convergents and on the other hand on the use of a CAA code, coupled with the CFD code, to properly propagate at a lower cost the high level acoustic waves from the jet near field towards the far field microphones. This methodology has demonstrated its benefits by producing very satisfactory results. Numerical velocity profiles are shown in very good agreement with the experimental measurements for several diameters downstream of the nozzle outlets. These results show that marked interactions between the two jets only occurs several diameters after the nozzle outlets. Regarding acoustics, the results are very encouraging. Considering the far field OASPL, the numerical vs. experimental deviation ranges from 0 to 3 dB. Higher levels in the azimuths perpendicular to the two jets with respect to the levels in the azimuths coplanar to the two jets are well recovered by the computation. These higher levels do not exactly reach the theoretical addition of two single jets noise, which suggests that acoustics source efficiency is reduced by interaction effects while lower levels in the coplanar plane traduce a probable masking effect.

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Intermittent modal coupling in screeching underexpanded circular twin jets

Abstract: Abstract

Cited by 18 publications

References 61 publications

Aeroacoustics of Twin Rectangular Jets Including Screech: Large-eddy Simulations with Experimental Validation

Aeroacoustics of Twin Rectangular Jets Including Screech: Large-eddy Simulations with Experimental Validation

Steady and unsteady coupling in twin weakly underexpanded round jets

Numerical Simulation of the Noise Radiated by Free Hot Supersonic Twin Jets

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