Steady and unsteady coupling in twin weakly underexpanded round jets

Wong, Tsz Y.M.; Stavropoulos, Michael N.; Beekman, Jayson R.; Towne, Aaron; Nogueira, Petrônio A.S.; Weightman, Joel; Edgington-Mitchell, Daniel

doi:10.1017/jfm.2023.275

Cited by 11 publications

(4 citation statements)

References 51 publications

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Section: Resultsmentioning

confidence: 99%

“…Work is currently underway to further characterize the intermittency observed in overexpanded cases. Variations in coupling strength and phase in underexpanded round twin jets have been explored in detail in a recent publication by Wong et al (2023). To gain a better insight of the baseline coupling and the effects of excitation, one M j (1.35, NPR = 2.97) case will be analysed in depth, as the other M j values have shown similar trends.…”

Section: Baselinementioning

confidence: 99%

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Active control of coupling and its effect on near-field pressure fluctuations in supersonic rectangular twin jets

Leahy,

Esfahani,

Webb

et al. 2023

Flow

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Supersonic rectangular twin jets (SRTJ) are of interest for current and future generations of tactical aircraft. However, the adverse effects of screech-loop coupling have previously been documented to significantly increase the near-field (NF) pressure fluctuations. These high-amplitude pressure fluctuations have the potential to fatigue and damage nearby aft components of the aircraft. Previous studies have documented that the NF pressure fluctuation level depends on the coupling of the jets: in-phase coupling along the twin jets’ minor axes produces stronger NF pressure fluctuations than that of out-of-phase coupling. The objective of this work is to further investigate the effects of coupling modes on NF pressure fluctuations in SRTJ and to mitigate the adverse effects of coupling using active flow control. Localized arc filament plasma actuators are employed to alter the SRTJs’ coupling mode by leveraging natural flow instabilities with minimal power input. A NF microphone array is used for simultaneous coupling and NF pressure fluctuation measurements. Schlieren imaging and spectral proper orthogonal decomposition are used to assess the effects of control on the flow field. The effect of excitation at various frequencies and actuation patterns on coupling and NF pressure fluctuations in different flow regimes are explored and discussed.

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Section: Resultsmentioning

confidence: 99%

Section: Baselinementioning

confidence: 99%

Active control of coupling and its effect on near-field pressure fluctuations in supersonic rectangular twin jets

Leahy,

Esfahani,

Webb

et al. 2023

Flow

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show abstract

“…Recent investigations have employed this technique to study the screech resonance mechanism in single round jets with very satisfactory results [18,34]. For twin-jet configurations, the application of SPOD to experimental schlieren datasets has also been successful to describe screech resonances [20,39,41,45,73], where the associated coherent structures are composed of waves which, within each jet, feature a spatial structure analogous to a single azimuthal mode in the equivalent isolated jet. Conversely, at other frequencies where mixing-layer noise is the dominant mechanism, SPOD based on schlieren images is not well suited for separating the toroidal and flapping modes of oscillation of the twin-jet system.…”

Section: Introductionmentioning

confidence: 99%

Eduction of coherent structures from schlieren images of twin jets using SPOD informed with momentum potential theory in the spectral domain

Padilla-Montero,

Rodríguez,

Jaunet

et al. 2024

Theor. Comput. Fluid Dyn.

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This work presents a methodology to extract coherent structures from high-speed schlieren images of turbulent twin jets which are more physically interpretable than those obtained with currently existing techniques. Recently, Prasad and Gaitonde (J Fluid Mech 940:1–11, 2022) introduced an approach which employs the momentum potential theory of Doak (J Sound Vib 131(1):67–90, 1989) to compute potential (acoustic and thermal) energy fluctuations from the schlieren images by solving a Poisson equation, and combines it with spectral proper orthogonal decomposition (SPOD) to educe coherent structures from the momentum potential field instead of the original schlieren field. While the latter field is dominated by a broad range of vortical fluctuations in the turbulent mixing region of unheated high-speed jets, the momentum potential field is governed by fluctuations which are intimately related to acoustic emission, and its spatial structure in the frequency domain is very organized. The proposed methodology in this paper improves the technique of Prasad and Gaitonde (J Fluid Mech 940:1–11, 2022) in three new ways. First, the solution of the Poisson equation is carried out in the frequency-wavenumber domain instead of the time-space domain, which simplifies and integrates the solution of the Poisson equation within the SPOD framework based on momentum potential fluctuations. Second, the issue of solving the Poisson equation on a finite domain with ad hoc boundary conditions is explicitly addressed, identifying and removing those unphysical harmonic components introduced in the solution process. Third, the solution of the SPOD problem in terms of momentum potential fluctuations is used to reconstruct schlieren SPOD fields associated with each mode, allowing the visualization of the obtained coherent structures also in terms of the density gradient. The method is applied here to schlieren images of a twin-jet configuration with a small jet separation at two supersonic operation conditions: a perfectly-expanded and an overexpanded one. The SPOD modes based on momentum potential fluctuations retain the wavepacket structure including the direct Mach-wave radiation, together with upstream- and downstream-traveling acoustic waves, similar to SPOD modes based on the schlieren images. However, for the same dataset, they result in a lower-rank decomposition than schlieren-based SPOD and provide an effective separation of twin-jet fluctuations into independent toroidal and flapping oscillations that are recovered as different SPOD modes. These coherent structures are more consistent with twin-jet wavepacket models available in the literature than those originally obtained with direct schlieren-based SPOD, facilitating their interpretation and comparison against theoretical analyses. Graphical abstract

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“…Recent investigations have employed this technique to study the screech resonance mechanism in single round jets with very satisfactory results [16,30]. For twin-jet configurations, the application of SPOD to experimental Schlieren data sets has also been successful to describe screech resonances [33,62,35], where the associated coherent structures are composed of waves which, within each jet, feature a spatial structure analogous to a single azimuthal mode in the equivalent isolated jet. Conversely, at other frequencies where mixing-layer noise is the dominant mechanism, SPOD based on Schlieren images is not well suited for separating the toroidal and flapping modes of oscillation of the twin-jet system.…”

Section: Introductionmentioning

confidence: 99%

Mean Flow and Linear Stability Analysis of Twin Supersonic Jets

Montero

Rodríguez

Jaunet

et al. 2023

AIAA AVIATION 2023 Forum

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This work proposes a methodology to improve the extraction of coherent structures associated with the generation of acoustic fluctuations in turbulent jets from high-speed Schlieren images. This methodology employs the momentum potential theory of Doak [14,24] to compute potential (acoustic and thermal) energy fluctuations from the Schlieren images by solving a Poisson equation, in the manner introduced by Prasad & Gaitonde [38]. The calculation of momentum potential fluctuations is then combined with the spectral proper orthogonal decomposition (SPOD) technique: the cross-spectral density is defined based on the momentum potential field, instead of the Schlieren images. While the latter are dominated by a broad range of vortical fluctuations in the turbulent mixing region of unheated high-speed jets, the momentum potential field is governed by acoustic fluctuations and its spatial structure in the frequency domain is remarkably coherent. This approach is applied here to Schlieren visualizations of a twin-jet configuration with a small jet separation and two supersonic operation conditions: a perfectly-expanded and a overexpanded one. The SPOD modes based on momentum potential fluctuations retain the wavepacket structure including the direct Mach-wave radiation together with upstream-and downstream-traveling acoustic waves, similar to SPOD modes based on the Schlieren images. However, they result in a remarkably lower-rank decomposition than Schlieren-based SPOD and, as opposed to the latter, provide an effective separation of twin-jet fluctuations into independent toroidal and flapping oscillations that are recovered as different SPOD modes.

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Steady and unsteady coupling in twin weakly underexpanded round jets

Cited by 11 publications

References 51 publications

Active control of coupling and its effect on near-field pressure fluctuations in supersonic rectangular twin jets

Active control of coupling and its effect on near-field pressure fluctuations in supersonic rectangular twin jets

Eduction of coherent structures from schlieren images of twin jets using SPOD informed with momentum potential theory in the spectral domain

Mean Flow and Linear Stability Analysis of Twin Supersonic Jets

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