Aerodynamics of Wedge-Shaped Deflectors for Jet Noise Reduction

Papamoschou, Dimitri; Vu, A.T.; Johnson, Andrew

doi:10.2514/6.2006-3655

Cited by 9 publications

(12 citation statements)

References 7 publications

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“…Surface pressure distributions on an external fan flow deflection (FFD) wedge were measured by Papamoschou et al [15]. Figure 18 summarizes their experimental configuration and key findings.…”

Section: A General Overviewmentioning

confidence: 99%

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Pylon-Based Jet Noise Suppressors

Papamoschou

2009

AIAA Journal

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This experimental investigation examined the potential of pylon-based deployable flaps to reduce jet noise of separate-flow turbofan engines with a bypass ratio of eight. The main function of the flap deflectors is to thicken the low-speed region surrounding the core jet in the downward and sideline directions. The study encompassed acoustic measurements, noise-source imaging, mean-velocity surveys, and aerodynamic estimates. Three types of deflectors were tested: solid flaps, porous flaps made of coarse perforation, and porous flaps made of fine perforation. It is shown that all the deflectors reduce noise sources near the end of the primary potential core. However, the solid flaps create excess noise in the vicinity of their location that can overwhelm this noise benefit, particularly at large polar angles. Porous flaps significantly reduce velocity gradients that cause excess noise. Noise generation from the perforations themselves can be shifted to very high frequency (rapidly attenuated by atmospheric absorption) by reducing the size of the perforation. Accordingly, the fine-perforation flaps provided superior acoustic results yielding effective perceived noise level benefits of 2.1 dB in the downward direction and 1.0 dB in the sideline direction. The static-thrust loss of these flaps is estimated at 0.7%.= fan nozzle exit height r = radial coordinate S = autospectrum of acoustic pressure Sr = Strouhal number U p = primary (core) exit velocity U s = secondary (fan) exit velocity u = axial mean velocity x = axial coordinate from exit of core nozzle y = transverse coordinate on symmetry plane z = transverse coordinate normal to symmetry plane = flap angle = polar angle from jet axis s = density of exit fan flow = azimuth angle measured from downward vertical = noise-source distribution

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Section: A General Overviewmentioning

confidence: 99%

“…In the aerodynamics experiments of [15], each half of the wedge was treated like an airfoil producing lift (side force) and drag. The sectional lift and drag coefficients were based on the chord length c of the wedge.…”

Section: B Drag Estimatementioning

confidence: 99%

Pylon-Based Jet Noise Suppressors

Papamoschou

2009

AIAA Journal

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“…Following the diagram in Fig. 16, the (7) where ix is illumination angle with respect to the u component of velocity and is identical to the illumination angle defined with respect to the freestream velocity ix = i . Combining Eqs.…”

Section: Body Force Model Formulation and Validationmentioning

confidence: 99%

“…6 Past experiments on large-scale FFD wedges have shown the local flow field to be highly three-dimensional with a strong localized upwash. 7 This behavior is explained using inviscid treatment of the flow approaching the wedge apex, as illustrated on the diagram of Fig. 3.…”

Section: Introductionmentioning

confidence: 99%

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Modeling of Wedge-Shaped Porous Flaps for Jet Noise Reduction

Xiong

Johnson

Liu

et al. 2011

49th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition

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RANS Analyses of Turbofan Nozzles With Internal Wedge Deflectors for Noise Reduction

DeBonis

2009

Journal of Fluids Engineering

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Computational fluid dynamics (CFD) was used to evaluate the flow field and thrust performance of a promising concept for reducing the noise at take-off of dual-stream turbofan nozzles. The concept, offset stream technology, reduces the jet noise observed on the ground by diverting (offsetting) a portion of the fan flow below the core flow, thickening and lengthening this layer between the high-velocity core flow and the ground observers. In this study a wedge placed in the internal fan stream is used as the diverter. Wind, a Reynolds averaged Navier–Stokes (RANS) code, was used to analyze the flow field of the exhaust plume and to calculate nozzle performance. Results showed that the wedge diverts all of the fan flow to the lower side of the nozzle, and the turbulent kinetic energy on the observer side of the nozzle is reduced. This reduction in turbulent kinetic energy should correspond to a reduction in noise. However, because all of the fan flow is diverted, the upper portion of the core flow is exposed to the freestream, and the turbulent kinetic energy on the upper side of the nozzle is increased, creating an unintended noise source. The blockage due to the wedge reduces the fan mass flow proportional to its blockage, and the overall thrust is consequently reduced. The CFD predictions are in very good agreement with experimental flow field data, demonstrating that RANS CFD can accurately predict the velocity and turbulent kinetic energy fields. While this initial design of a large scale wedge nozzle did not meet noise reduction or thrust goals, this study identified areas for improvement and demonstrated that RANS CFD can be used to improve the concept.

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Aerodynamics of Wedge-Shaped Deflectors for Jet Noise Reduction

Cited by 9 publications

References 7 publications

Pylon-Based Jet Noise Suppressors

Pylon-Based Jet Noise Suppressors

Modeling of Wedge-Shaped Porous Flaps for Jet Noise Reduction

RANS Analyses of Turbofan Nozzles With Internal Wedge Deflectors for Noise Reduction

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