Acoustics and Thrust of Quiet Separate-Flow High-Bypass-Ratio Nozzles

Saiyed, Naseem H.; Mikkelsen, Kevin L.; Bridges, Jackie

doi:10.2514/2.1986

Cited by 95 publications

(33 citation statements)

References 5 publications

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“…Since then, considerable efforts have led to the currently implemented solution based on serrations in the nozzle exit called chevrons. Chevron effects were notably described in [2][3][4], with an evaluation of the thrust loss due to this passive device which provides nonnegligeable cumulative effects on long trips. To limit the thrust penalty, control systems have to be activated only when needed.…”

mentioning

confidence: 99%

Jet-Noise Reduction by Impinging Microjets: an Acoustic Investigation Testing Microjet Parameters

et al. 2008

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A system of 36 impinging microjets was implemented on a round jet of Mach number 0.9, and the noise reduction was studied as a function of the microinjection mass flux, the number of microjets blowing, the layout of the blowing microjets, and the microjet diameter. Depending on the microinjection flux parameters, overall jet-noise reduction varied from 0 to 1.5 dB, showing some nonmonotonic behavior due to the change between subsonic to supersonic microjet regimes. The study of the microjet layout showed that the noise reduction decreased when the microjets were too close to each other and that certain configurations of microjet pairs could be favorable; this can be related to the flow structures induced by the microjets. Spectral analysis disclosed different control mechanisms, with highfrequency regeneration for high-injection flux, local control behavior at midfrequencies, and global behavior at low frequencies.

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confidence: 99%

Jet-Noise Reduction by Impinging Microjets: an Acoustic Investigation Testing Microjet Parameters

et al. 2008

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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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“…Despite this, passive methods have found wide application, particularly for aerospace engine applications, and many investigations have been described [27][28][29][30][31][32][33][34][35][36]. Related reviews have been given by Gutmark and Grinstein [26], and Zaman, Bridges and Huff [25].…”

Section: Control Methodsmentioning

confidence: 99%

“…Ibrahim et al [41], for example, made experiments on a compressible jet and gained a measure of control through the action of a series of pulsed micro-jets located around the periphery of the nozzle. In complete contrast, Saiyed et al [47] examined the steady-flow performance of a number of high-bypass-ratio nozzles used in aero-engines.…”

Section: Control Methodsmentioning

confidence: 99%

On the development of a turbulent jet subjected to aerodynamic excitation in the helical mode

Zhang

Turner

2016

Experimental Thermal and Fluid Science

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Aerodynamic excitation has been used to introduce energy into the free shear layer at the outer edges of an axisymmetric free jet by injecting a pulsating secondary jet through a thin annular nozzle that surrounds and is concentric with the primary nozzle. In the present study, it has been found that the rate of mixing can be increased if the pulsations are applied in a sequential fashion around the circumference of the jet, so as to create helical vortices in the region close to the nozzle exit plane. Flow visualisation confirms the helical nature of the vortices and shows how these vortices are convected downstream with the main flow, strongly influencing the development of the primary jet. Two-component laser Doppler anemometry (LDA) was used to make measurements of the flow distributions in the developing jet for a number of flow conditions. These results have been analysed to extract various measures of the turbulent mixing, including the time averaged velocity distributions, and the higher order moments and spectral distributions of the turbulent velocity fluctuations.The present data confirm that introducing the excitation in a helical mode leads to an increased rate of entrainment and more rapid mixing, when compared with the toroidal excitation used in previous studies. These changes significantly increase the rate of development of the jet in the axial direction.

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Acoustics and Thrust of Quiet Separate-Flow High-Bypass-Ratio Nozzles

Cited by 95 publications

References 5 publications

Jet-Noise Reduction by Impinging Microjets: an Acoustic Investigation Testing Microjet Parameters

Jet-Noise Reduction by Impinging Microjets: an Acoustic Investigation Testing Microjet Parameters

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

On the development of a turbulent jet subjected to aerodynamic excitation in the helical mode

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