Acoustic and Flow-Field Characteristics of Shock-cell Noise from Dual Flow Nozzles

Bhat, Thonse R. S.; Ganz, Ulrich; Guthrie, Ann

doi:10.2514/6.2005-2929

Cited by 15 publications

(13 citation statements)

References 7 publications

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“…Their results indicate that the peaks associated with the higher order waveguide modes become more pronounced with increasing freestream Mach number. Bhat et al 10 documented model scale shockcell noise measurements in the Boeing Low Speed Aeroacoustic Facility and showed that shockcell noise resulting from a dual flow co-annular jet rig does not monotonically increase with jet Mach number but is a complex function of the Mach numbers of the two jets.…”

Section: Rr R-core Chevron R-fan Chevronmentioning

confidence: 99%

Flight Test Results for Uniquely Tailored Propulsion Airframe Aeroacoustic Chevrons: Shockcell Noise

Mengle

Ganz

Nesbitt

et al. 2006

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

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Azimuthally varying chevrons (AVC) which have been uniquely tailored to account for the asymmetric propulsion-airframe aeroacoustic interactions have recently shown significant reductions in jet-related community noise at low-speed take-off conditions in scale model tests of coaxial nozzles with high bypass ratio. There were indications that such AVCs may also provide shockcell noise reductions at high cruise speeds. This paper describes the flight test results when one such AVC concept, namely, the T-fan chevrons with enhanced mixing near the pylon, was tested at full-scale on a modern large twin-jet aircraft (777-300ER) with focus on shockcell noise at mid-cruise conditions. Shockcell noise is part of the interior cabin noise at cruise conditions and its reduction is useful from the viewpoint of passenger comfort. Noise reduction at the source, in the exhaust jet, especially, at low frequencies, is beneficial from the perspective of reduced fuselage sidewall acoustic lining. Results are shown in terms of unsteady pressure spectra both on the exterior surface of the fuselage at several axial stations and also microphone arrays placed inside the fuselage aft of the engine. The benefits of T-fan chevrons, with and without conventional chevrons on the core nozzle, are shown for several engine operating conditions at cruise involving supersonic fan stream and subsonic or supersonic core stream. The T-fan AVC alone provides up to 5 dB low-frequency noise reduction on the fuselage exterior skin and up to 2 dB reduction inside the cabin. Addition of core chevrons appears to increase the higher frequency noise. This flight test result with the previous model test observation that the Tfan AVCs have hardly any cruise thrust coefficient loss (< 0.05%) make them viable candidates for reducing interior cabin noise in high bypass ratio engines. Nomenclature

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Section: Rr R-core Chevron R-fan Chevronmentioning

confidence: 99%

Flight Test Results for Uniquely Tailored Propulsion Airframe Aeroacoustic Chevrons: Shockcell Noise

Mengle

Ganz

Nesbitt

et al. 2006

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

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“…Broadband shock noise resulting from interactions between stream disturbances and shock waves in the jet tends to dominate the acoustic spectra at upstream and broadside observation angles 1,2,3 . In dual stream jets, the production of broadband shock noise depends on the fan pressure relative to the core pressure due to the complicated shock cell structure in the flow 4,5 . Screech tones are commonly observed in acoustic spectra acquired at upstream and broadside observation angles of cold laboratory jets.…”

Section: Introductionmentioning

confidence: 99%

Impact of Azimuthally Controlled Fluidic Chevrons on Jet Noise

Henderson

Norum

2008

14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference)

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The impact of azimuthally controlled air injection on broadband shock noise and mixing noise for single and dual stream jets was investigated. The single stream experiments focused on noise reduction for low supersonic jet exhausts. Dual stream experiments included high subsonic core and fan conditions and supersonic fan conditions with transonic core conditions. For the dual stream experiments, air was injected into the core stream. Significant reductions in broadband shock noise were achieved in a single jet with an injection mass flow equal to 1.2% of the core mass flow. Injection near the pylon produced greater broadband shock noise reductions than injection at other locations around the nozzle periphery. Air injection into the core stream did not result in broadband shock noise reduction in dual stream jets. Fluidic injection resulted in some mixing noise reductions for both the single and dual stream jets. For subsonic fan and core conditions, the lowest noise levels were obtained when injecting on the side of the nozzle closest to the microphone axis.

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“…Computationally, the surface porosity has been modeled very effectively with boundary conditions extensively in previous studies by Elmiligui et al 11 and others. Bhat et al 12 recently conducted experiments with a model-scale axisymmetric separate flow nozzle. Results indicated a strong relationship between the amplitude of the shock-cell structures and the radiated noise.…”

Section: Introductionmentioning

confidence: 99%

“…Results indicated a strong relationship between the amplitude of the shock-cell structures and the radiated noise. Given this proven relationship between shock cell strength and broadband shock associated noise intensity, 3,12 this study will only address shock cell strength rather than the predicted noise of the shock cells.…”

Section: Introductionmentioning

confidence: 99%

Computational Analysis of the Effect of Porosity on Shock Cell Strength at Cruise

Massey¹,

Elmiligui

Thomas

et al. 2006

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

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A computational flow field analysis is presented of the effect of core cowl porosity on shock cell strength for a modern separate flow nozzle at cruise conditions. The goal of this study was to identify the primary physical mechanisms by which the application of porosity can reduce shock cell strength and hence the broadband shock associated noise. The flow is simulated by solving the asymptotically steady, compressible, Reynoldsaveraged Navier-Stokes equations on a structured grid using an implicit, up-wind, flux-difference splitting finite volume scheme. The standard two-equation k − ε turbulence model with a linear stress representation is used with the addition of a eddy viscosity dependence on total temperature gradient normalized by local turbulence length scale. Specific issues addressed in this study were the optimal area required to weaken a shock impinging on the core cowl surface and the optimal level of porosity and placement of porous areas for reduction of the overall shock cell strength downstream. Two configurations of porosity were found to reduce downstream shock strength by approximately 50%.

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Acoustic and Flow-Field Characteristics of Shock-cell Noise from Dual Flow Nozzles

Cited by 15 publications

References 7 publications

Flight Test Results for Uniquely Tailored Propulsion Airframe Aeroacoustic Chevrons: Shockcell Noise

Flight Test Results for Uniquely Tailored Propulsion Airframe Aeroacoustic Chevrons: Shockcell Noise

Impact of Azimuthally Controlled Fluidic Chevrons on Jet Noise

Computational Analysis of the Effect of Porosity on Shock Cell Strength at Cruise

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