Coherent structure and sound production in the helical mode of a screeching axisymmetric jet

Edgington-Mitchell, Daniel; Oberleithner, Kilian; Honnery, Damon; Soria, Julio

doi:10.1017/jfm.2014.173

Cited by 115 publications

(96 citation statements)

References 42 publications

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“…This method is only applicable if a pair of POD modes can be identified that span the subspace of the oscillatory motion. The same method was previously applied to reconstruct the dominant coherent structures in supersonic jets (Edgington-Mitchell et al 2014) and in jets with swirl (Oberleithner et al 2011;Stöhr et al 2011;Oberleithner et al 2012). In the present study, the fundamental and higher order harmonics clearly pair in POD space with stepwise decreasing energy content.…”

Section: Decomposition Of the Velocity Fieldsupporting

confidence: 55%

Mean flow stability analysis of oscillating jet experiments

2014

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Linear stability analysis is applied to the mean flow of an oscillating round jet with the aim to investigate the robustness and accuracy of mean flow stability wave models. The jet's axisymmetric mode is excited at the nozzle lip through a sinusoidal modulation of the flow rate at amplitudes ranging from 0.1 % to 100 %. The instantaneous flow field is measured via particle image velocimetry and decomposed into a mean and periodic part utilizing proper orthogonal decomposition. Local linear stability analysis is applied to the measured mean flow adopting a weakly nonparallel flow approach. The resulting global perturbation field is carefully compared to the measurements in terms of spatial growth rate, phase velocity, and phase and amplitude distribution. It is shown that the stability wave model accurately predicts the excited flow oscillations during their entire growth phase and during a large part of their decay phase. The stability wave model applies over a wide range of forcing amplitudes, showing no pronounced sensitivity to the strength of nonlinear saturation. The upstream displacement of the neutral point and the successive reduction of gain with increasing forcing amplitude is very well captured by the stability wave model. At very strong forcing (> 40%), the flow becomes essentially stable to the axisymmetric mode. For these extreme cases, the prediction deteriorates from the measurements due to an interaction of the forced wave with the geometric confinement of the nozzle. Moreover, the model fails far downstream in a region where energy is transferred from the oscillation back to the mean flow. This study supports previously conducted mean flow stability analysis of self-excited flow oscillations in the cylinder wake and in the vortex breakdown bubble and extends the methodology to externally forced convectively unstable flows. The high accuracy of mean flow stability wave models as demonstrated here is of great importance for the analysis of coherent structures in turbulent shear flows.

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Section: Decomposition Of the Velocity Fieldsupporting

confidence: 55%

Mean flow stability analysis of oscillating jet experiments

2014

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“…The largest cross-sectional velocity fluctuation intensity, however, is found near the jet axis. Furthermore, it should be mentioned that the current turbulence intensity distributions show a strong similarity to those observed in the measurement of a screeching axisymmetric jet in the helical C mode [32], where Proper orthogonal decomposition (POD) method was used to separate the coherent structure from the random axial stresses.…”

Section: Noise Sources Of Screech Tonesmentioning

confidence: 71%

Numerical Study of Noise Characteristics in Overexpanded Jet Flows

Liu¹,

Corrigan²,

Kailasanath³

et al. 2015

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Standard Form 298 (Rev. 8-98)Prescribed by ANSI Std. Z39.18Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Noise characteristics in shock-containing jets at an overexpanded jet condition have been investigated. Total temperature ratios of 1.0 (cold), 2.0, and 3.0 are considered. The cold jet is a highly screeching jet. Frequency-wavenumber Fourier analysis is employed to examine the wave characteristics of pressure waves along the lip line and also along a near-field conical surface. It is found that the radiating portion of the pressure wave intensity increases with the jet temperature, but the hydrodynamic portion is much less sensitive to the change of the jet temperature. The near-field noise intensity associated with the Mach wave radiation is observed over a large axial distance, and the Mach wave radiation extends to much higher frequencies in heated jets. The peak radiation direction in the cold jet is dominated by the axisymmetric mode, but the directions around the sideline show a much weaker azimuthal dependence. Furthermore, the axial locations of lip-line pressure peak intensities at the screech frequency are near the axial locations of shock-cell tips. A reinforcing loop between upstream/downstream propagating waves and the induced shock-cell coherent oscillatory motion is observed in the highly screeching jet. The formation of this reinforcing loop requires a match of the peak phase velocities between upstream and downstream propagating waves. This phase velocity match exists in the highly screeching cold jet, but not in the weakly screeching heated jets. It appears that the phase velocity match that sustains the reinforcing loop is important to the screech generation, and the phase velocity mismatch in heated jets is believed to be an important cause of the screech intensity reduction. REPORT TYPE 1. REPORT DATE (DD-MM-YYYY) TITLE AND SUBTITLE AUTHOR(S) PERFORMING ORGANIZATION REPORT NUMBER PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) SPONSOR / MONITOR'S ACRONYM(S) 9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) SPONSOR / MONITOR'S REPORT NUMBER(S)

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“…8a have been previously identified as representative of a B type flapping instability mode (Edgington-Mitchell et al 2014). Figure 8b, c shows two-point correlation results for the single tab case.…”

Section: Instability Mode Of a Tabbed Jetmentioning

confidence: 87%

“…The microphone was placed 10D from the target position at x=D ¼ 4, an estimate of the dominant screech sound source location for the range of NPR covered. This estimate is based on previous publications suggesting that the dominant acoustic sources in the jet are shock cells three and four (Edgington-Mitchell et al 2014;Shen and Tam 2002;Umeda and Ishii 2002;Gao and Li 2010). It should be noted that the location of the dominant acoustic features of the jet do not correspond with the image field-of-view presented in Table 1.…”

Section: Effect Of Tabs On Acoustic Fieldmentioning

confidence: 97%

“…When the shear layer at the nozzle lip is excited by an acoustic disturbance, instability waves are introduced to the jet that travel downstream in the form of coherent shear layer vortices (Suzuki and Lele 2003) that grow larger and more influential as they convect further downstream. Where the vortices produce large fluctuations in shear layer vorticity, the shocks within the jet can transmit energy through the jet boundary in the form of an acoustic wave (Edgington-Mitchell et al 2014). These waves propagate upstream outside the jet mixing region to again excite the shear layer and close the feedback loop.…”

Section: Introductionmentioning

confidence: 99%

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Visualisation of underexpanded jet flowfields in the presence of an intrusive tab

Johnston

Edgington-Mitchell

2015

J Vis

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This paper investigates the influence of a single intrusive tab has on the flowfield of a supersonic jet. When a tab is added to the jet, an increase in the fundamental screech frequency is observed in acoustic spectra. High resolution schlieren imaging reveals alteration of both the shock structure and preferred instability mode in the jet. Two-point spatial correlation of schlieren images shows the transition from a lateral flapping mode to a punctuated toroid screech mode. This change in dominant instability mode produces a change in coherent structure wavelength that correlates well to the observed screech frequency shift in the acoustic data. The high quality of the schlieren images also allows the counter-rotating vortex pair produced by an individual tab to be identified. Images of the radial density gradient are used to estimate vortex pair location, and a statistical estimate for the trajectory of the vortex pair is produced. The vortex pair path identification technique shows that the path of the vortex pair is constrained close to the exit of the nozzle and increasingly variant in space with greater downstream distance. The vortex trajectory is shown to alter the sonic line and thus the spatial extent of the embedded shock structures.

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Coherent structure and sound production in the helical mode of a screeching axisymmetric jet

Cited by 115 publications

References 42 publications

Mean flow stability analysis of oscillating jet experiments

Mean flow stability analysis of oscillating jet experiments

Numerical Study of Noise Characteristics in Overexpanded Jet Flows

Visualisation of underexpanded jet flowfields in the presence of an intrusive tab

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