Computational Analysis of the Flow and Acoustic Effects of Jet-Pylon Interaction

Hunter, Craig A.; Thomas, Russell H.; Pao, S. Paul; Elmiligui, Alaa A.; Massey, Steven J.; Aeronautics, Eagle

doi:10.2514/6.2005-3083

Cited by 17 publications

(14 citation statements)

References 7 publications

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“…NASA and industry had already developed considerable experience that gave NASA the confidence that this key assumption could be realized. This understanding had been developed through a series of extensive experimental and computational studies beginning in 2002 through 2005 on the fundamental effects of jet noise reduction and jet noise source re-distribution with chevron and pylon effects [3][4][5][6][7][8][9][10][11] . Building on this information by 2009, ERA had already developed a technical path for an HWB concept to reach the noise goal.…”

Section: Introductionmentioning

confidence: 99%

High Bypass Ratio Jet Noise Reduction and Installation Effects Including Shielding Effectiveness

Thomas

Czech

Doty

2013

51st AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition

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An experimental investigation was performed to study the propulsion airframe aeroacoustic installation effects of a separate flow jet nozzle with a Hybrid Wing Body aircraft configuration where the engine is installed above the wing. Prior understanding of the jet noise shielding effectiveness was extended to a bypass ratio ten application as a function of nozzle configuration, chevron type, axial spacing, and installation effects from additional airframe components. Chevron types included fan chevrons that are uniform circumferentially around the fan nozzle and T-fan type chevrons that are asymmetrical circumferentially. In isolated testing without a pylon, uniform chevrons compared to T-fan chevrons showed slightly more low frequency reduction offset by more high frequency increase. Phased array localization shows that at this bypass ratio chevrons still move peak jet noise source locations upstream but not to nearly the extent, as a function of frequency, as for lower bypass ratio jets. For baseline nozzles without chevrons, the basic pylon effect has been greatly reduced compared to that seen for lower bypass ratio jets. Compared to Tfan chevrons without a pylon, the combination with a standard pylon results in more high frequency noise increase and an overall higher noise level. Shielded by an airframe surface 2.17 fan diameters from nozzle to airframe trailing edge, the T-fan chevron nozzle can produce reductions in jet noise of as much as 8 dB at high frequencies and upstream angles. Noise reduction from shielding decreases with decreasing frequency and with increasing angle from the jet inlet. Beyond an angle of 130 degrees there is almost no noise reduction from shielding. Increasing chevron immersion more than what is already an aggressive design is not advantageous for noise reduction. The addition of airframe control surfaces, including vertical stabilizers and elevon deflection, showed only a small overall impact. Based on the test results, the best overall nozzle configuration design was selected for application to the N2A Hybrid Wing Body concept that will be the subject of the NASA Langley 14 by 22 Foot Subsonic Tunnel high fidelity aeroacoustic characterization experiment. The best overall nozzle selected includes T-fan type chevrons, uniform chevrons on the core nozzle, and no additional pylon of the type that created a strong acoustic effect at lower bypass ratios. The T-fan chevrons are oriented azimuthally away from the ground observer locations. This best overall nozzle compared to the baseline nozzle was assessed, at equal thrust, to produce sufficient installed noise reduction of the jet noise component to enable the N2A HWB to meet NASA's noise goal of 42 dB cumulative below Stage 4. = total temperature ratio of the secondary fan stream θ = polar directivity angle, degrees, jet axis at 180 degrees ψ = azimuthal directivity angle, degrees

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Section: Introductionmentioning

confidence: 99%

High Bypass Ratio Jet Noise Reduction and Installation Effects Including Shielding Effectiveness

Thomas

Czech

Doty

2013

51st AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition

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“…8 In this study, Jet3D is utilized to produce noise source maps which are correlated to the local flow features. This approach was recently successfully applied to separate flow nozzles with an isolated pylon by Hunter et al 9 The computational domain extends six core diameters upstream from the fan exit, 30 downstream and eight radially. Transitions from boundary to shear layer grids are smoothed to aid convergence.…”

Section: Methodsmentioning

confidence: 99%

“…5,6,9,19 The additional resolution is aimed at better resolving the complex flow initiated by both fan and core chevrons. All surfaces are gridded and run as viscous with the exception of the very small tip region of the plug and the very thin nozzle trailing edges.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Computational Analysis of a Chevron Nozzle Uniquely Tailored for Propulsion Airframe Aeroacoustics

Massey¹,

Elmiligui

Hunter

et al. 2006

12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference)

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A computational flow field and predicted jet noise source analysis is presented for asymmetrical fan chevrons on a modern separate flow nozzle at take off conditions. The propulsion airframe aeroacoustic asymmetric fan nozzle is designed with an azimuthally varying chevron pattern with longer chevrons close to the pylon. A baseline round nozzle without chevrons and a reference nozzle with azimuthally uniform chevrons are also studied. The intent of the asymmetric fan chevron nozzle was to improve the noise reduction potential by creating a favorable propulsion airframe aeroacoustic interaction effect between the pylon and chevron nozzle. This favorable interaction and improved noise reduction was observed in model scale tests and flight test data and has been reported in other studies. The goal of this study was to identify the fundamental flow and noise source mechanisms. The flow simulation uses the asymptotically steady, compressible Reynoldsaveraged Navier-Stokes equations on a structured grid. Flow computations are performed using the parallel, multi-block, structured grid code PAB3D. Local noise sources were mapped and integrated computationally using the Jet3D code based upon the Lighthill Acoustic Analogy with anisotropic Reynolds stress modeling. In this study, trends of noise reduction were correctly predicted. Jet3D was also utilized to produce noise source maps that were then correlated to local flow features. The flow studies show that asymmetry of the longer fan chevrons near the pylon work to reduce the strength of the secondary flow induced by the pylon itself, such that the asymmetric merging of the fan and core shear layers is significantly delayed. The effect is to reduce the peak turbulence kinetic energy and shift it downstream, reducing overall noise production. This combined flow and noise prediction approach has yielded considerable understanding of the physics of a fan chevron nozzle designed to include propulsion airframe aeroacoustic interaction effects. Nomenclature AxiAxisymmetric fan and core nozzle configuration bb Baseline nozzle configuration with pylon and without chevrons D Core exit diameter k Mass averaged non-dimensional turbulence intensity, see equation (1) k Turbulence kinetic energy per unit mass (TKE)

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“…PAA technology options were selected based on prior PAA research of interest for conventional configurations, specifically the acoustic effect of the engine pylon [6][7][8][9][10][11] and unique chevron nozzles that were designed to interact favorably with the effect of the pylon [12][13][14] . In a study by Nesbitt et al 15 it was reported that chevrons also impact jet noise source locations and their significance in the context of far-field extrapolation.…”

mentioning

confidence: 99%

Propulsion Airframe Aeroacoustic Integration Effects for a Hybrid Wing Body Aircraft Configuration

Thomas

Czech

Elkoby

2010

16th AIAA/CEAS Aeroacoustics Conference

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An extensive experimental investigation was performed to study the propulsion airframe aeroacoustic effects of a high bypass ratio engine for a hybrid wing body aircraft configuration where the engine is installed above the wing. The objective was to provide an understanding of the jet noise shielding effectiveness as a function of engine gas condition and location as well as nozzle configuration. A 4.7% scale nozzle of a bypass ratio seven engine was run at characteristic cycle points under static and forward flight conditions. The effect of the pylon and its orientation on jet noise was also studied as a function of bypass ratio and cycle condition. The addition of a pylon yielded significant spectral changes lowering jet noise by up to 4dB at high polar angles and increasing it by 2 to 3dB at forward angles. In order to assess jet noise shielding, a planform representation of the airframe model, also at 4.7% scale was traversed relative to the jet nozzle from downstream to several diameters upstream of the wing trailing edge. Installations at two fan diameters upstream of the wing trailing edge provided only limited shielding in the forward arc at high frequencies for both the axisymmetric and a conventional round nozzle with pylon. This was consistent with phased array measurements suggesting that the high frequency sources are predominantly located near the nozzle exit and, consequently, are amenable to shielding. The mid to low frequencies sources were observed further downstream and shielding was insignificant. Chevrons were designed and used to impact the distribution of sources with the more aggressive design showing a significant upstream migration of the sources in the mid frequency range. Furthermore, the chevrons reduced the low frequency source levels and the typical high frequency increase due to the application of chevron nozzles was successfully shielded. The pylon was further modified with a technology that injects air through the shelf of the pylon which was effective in reducing low frequency noise and moving jet noise sources closer to the nozzle exit. In general, shielding effectiveness varied as a function of cycle condition with the cutback condition producing higher shielding compared to sideline power. The configuration with a more strongly immersed chevron and a pylon oriented opposite to the microphones produced the largest reduction in jet noise. In addition to the jet noise source, the shielding of a broadband point noise source was documented with up to 20 dB of noise reduction at directivity angles directly under the shielding surface. Nomenclature

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Computational Analysis of the Flow and Acoustic Effects of Jet-Pylon Interaction

Cited by 17 publications

References 7 publications

High Bypass Ratio Jet Noise Reduction and Installation Effects Including Shielding Effectiveness

High Bypass Ratio Jet Noise Reduction and Installation Effects Including Shielding Effectiveness

Computational Analysis of a Chevron Nozzle Uniquely Tailored for Propulsion Airframe Aeroacoustics

Propulsion Airframe Aeroacoustic Integration Effects for a Hybrid Wing Body Aircraft Configuration

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