Far-Field Acoustic Investigation into Chevron Nozzle Mechanisms and Trends

Callender, Bryan; Gutmark, Ephraim; Martens, Steven

doi:10.2514/1.6150

Cited by 181 publications

(71 citation statements)

References 14 publications

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“…The growth and decay for the pressure wavepackets have been clearly demonstrated. Moreover, it is found that the noise is produced from the region near the end of the potential core, and mainly radiates towards shallow polar angles, which are in agreement with experimental and LES results [2,16]. In general, the beam patterns produced by the wavepackets in two jets show no qualitative difference.…”

Section: Acoustic Efficiency Of Linear Wavepacketssupporting

confidence: 78%

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Instability waves and low-frequency noise radiation in the subsonic chevron jet

Ran

Wan

et al. 2017

Acta Mech. Sin.

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Spatial instability waves associated with lowfrequency noise radiation at shallow polar angles in the chevron jet are investigated and are compared to the round counterpart. The Reynolds-averaged Navier-Stokes equations are solved to obtain the mean flow fields, which serve as the baseflow for linear stability analysis. The chevron jet has more complicated instability waves than the round jet, where three types of instability modes are identified in the vicinity of the nozzle, corresponding to radial shear, azimuthal shear, and their integrated effect of the baseflow, respectively. The most unstable frequency of all chevron modes and round modes in both jets decrease as the axial location moves downstream. Besides, the azimuthal shear effect related modes are more unstable than radial shear effect related modes at low frequencies. Compared to a round jet, a chevron jet reduces the growth rate of the most unstable modes at downstream locations. Moreover, linearized Euler equations are employed to obtain the beam pattern of pressure generated by spatially evolving instability waves at a dominant low frequency St = 0.3, and the acoustic efficiencies of these linear wavepackets are evaluated for both jets. It is found that the acoustic efficiency of linear wavepacket is able to be reduced greatly in the chevron jet, compared to the round jet.

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Section: Acoustic Efficiency Of Linear Wavepacketssupporting

confidence: 78%

“…Refs. [1,2], the influence of chevron parameters and the reduction mechanisms of dominant low-frequency noise at shallow polar angles are still poorly understood, which imposes serious problems on design and optimization of parameters of a chevron nozzle. The main evaluation methods, i.e.…”

Section: Introductionmentioning

confidence: 99%

Instability waves and low-frequency noise radiation in the subsonic chevron jet

Ran

Wan

et al. 2017

Acta Mech. Sin.

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“…For instance, if one aims at investigating the effects of devices such as chevrons, tabs or microjets, it should be required to ensure that the uncertainties due to the inflow conditions are lower than the variations of the sound pressure levels around −3 dB expected according to experiments. [40][41][42][43] For practical applications, vortex pairing noise appears in particular to be attenuated, which has motivated the developments of LES of initially turbulent jets. 12,44 especially to Jean-Michel Dupays for his technical assistance.…”

Section: Discussionmentioning

confidence: 99%

Influence of the Nozzle-Exit Boundary-Layer Thickness on the Flow and Acoustic Fields of Initially Laminar Jets

Bailly

2009

15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)

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Round jets originating from a pipe nozzle are computed by Large-Eddy Simulations (LES) to investigate the effects of the nozzle-exit conditions on the flow and sound fields of initially laminar jets. The jets are at Mach number 0.9 and Reynolds number 10 5 , and exhibit exit boundary layers characterized by Blasius velocity profiles, maximum rootmean-square axial velocity fluctuations between 0.2% and 1.9% of the jet velocity, and momentum thicknesses varying from 0.003 to 0.023 times the jet radius. The far-field noise is determined from the LES data on a cylindrical surface by solving the acoustic equations. Jets with thinner boundary layer develop earlier but at a slower rate, yielding longer potential cores and lower centerline turbulent intensities comparing well with measurements at high Reynolds numbers. In all jets the shear-layer transition is dominated by vortex rolling-ups and pairings, which generate strong components in the noise spectra. Just adding random disturbances of low magnitude in the nozzle however leads to weaker rolling-up and pairing processes, thus significantly reducing their contributions to the sound field. This high sensitivity to the initial conditions is in good agreement with experimental observations.

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“…14 indicates that limited SPL increases at Strouhal numbers greater than 2. In the past, chevrons have been shown to increase small scale mixing noise as a result of increased near nozzle small scale turbulence production in both the subsonic and supersonic regimes [56,8]. Consequently, any observed increases in high frequency noise at Φ¼150°is a combined result of the increase of BSAN frequency and this redistribution of large scale structures into smaller scales [5].…”

Section: Acoustic Fieldmentioning

confidence: 99%