Finite length tuning for low frequency lining design

Unruh, James F.

doi:10.1016/0022-460x(76)90663-5

Cited by 36 publications

(14 citation statements)

References 1 publication

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“…Since the liner is quite short the higher radial modes contribute significantly to the overall suppression. This effect is very pronounced at low frequencies [17] and, as shown herein, for higher order modes which have relatively long axial wave lengths (similar to low frequency sound propagation).…”

Section: Discussion Of Resultsmentioning

confidence: 58%

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Finite Element-Integral Acoustic Simulation of JT15D Turbofan Engine

Baumeister

Horowitz

1984

Journal of Vibration and Acoustics

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An .iterative finite element-integral technique is used to predict the sound field radlatedfrom the JTl5D turbofan inlet. The soundfield is divided into two regions: the sound field within and near the inlet which is computed using the finite element method, and the radiation field beyond the inlet which is calculated using an integral solution technique. The velocity potential formulation of the acoustic wave equation was employed in the program. For some single mode JTJ5D datil, the theory and experiment are in good agreement for the far field radiation pattern as well as suppressor attenuation. Also, the computer program is used to simulate flight effects that cannot be performed on a ground static test stand.

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Section: Discussion Of Resultsmentioning

confidence: 58%

“…Generally, as shown by Unruh [17] the optimum resistance for a finite length liner will be lower than the single mode value due to the generation of higher order modes. Individually, the higher order modes have lower optimum impedance.…”

Section: Discussion Of Resultsmentioning

confidence: 98%

Finite Element-Integral Acoustic Simulation of JT15D Turbofan Engine

Baumeister

Horowitz

1984

Journal of Vibration and Acoustics

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“…This type of axially segmented liner is of interest because it could be used to increase the attenuation of fan tones at high supersonic fan speeds. J. F. Unruh (1976) first examined how the liner's length, as well as its impedance, may be tuned to optimize attenuation. Also, both K. J.…”

Section: Acoustic Linermentioning

confidence: 99%

Main Fan Noise Mitigation Technologies in Turbofan Engines

Ommi

Azimi

2014

Aviation

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abstract. Aircraft noise and emissions have been of concern since the beginning of commercial aviation. The continuing growth in air traffic and increasing public awareness have made environmental considerations one of the most critical aspects of commercial aviation today. To deal with this problem, aircraft manufacturers and public establishments are engaged in research on technical and theoretical approaches for noise reduction concepts that should be applied to new aircraft. While jet noise was the dominating contributor in the early jet engine designs, the noise emitted by the fan has become important with the reduction in jet speed and its control requiring an immense research effort. This paper concerns the main fan noise mitigation technologies in turbofan engines.

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“…Needless to say multimode broadband calculations of this type require a large amount of computer processing time and as a result do not lend themselves to rapid, convenient optimization routines. Elsewhere, another method that has arisen for the mode-matching process between liners is based on the Galerkin Method of Weighted Residuals 9 . This involves matching the pressure and velocity differences across the interfaces via an integration so that the modal constants can be set appropriately.…”

Section: Introductionmentioning

confidence: 99%

Optimization of Annular and Cylindrical Liners for Mixed Exhaust Aeroengines

Law

2007

13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference)

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The increase in bypass ratios for modern day turbofan engines has led to fan rearward broadband noise emerging as one of the principal aircraft noise sources. The most widespread method for mitigating this noise source is the installation of acoustic liners in the ducting downstream of the fan. Mixed exhaust designs have the potential to be quieter than a three quarter cowl aeroengine due to the additional surface available for liner application. As a result, the Silent Aircraft concept design contains an embedded distributed propulsion system to exploit this opportunity. This paper outlines a suitable method for optimizing the annular and cylindrical liners that make up the exhaust system. To gain maximum benefit, liners should be designed to absorb the modal disturbances that are the most significant for an observer on the ground. The optimization uses an advanced noise footprint cost function to achieve this. Consequently, the liners and the length of the installation have been chosen to meet the aggressive noise target set for the aircraft. In addition, we explore the effect that modal scattering between axial liner junctions can have on the acoustic performance of the system. We find that energy interchange between radial modes will often have a detrimental effect on the overall attenuation, although this can be addressed by selecting the order of the liners in a more considered way. The assumption that scattering between liners can be neglected during optimization to allow design of the individual components therefore appears to be valid in this case. However, subsequent attention has to be directed to the order in which they are placed. Current and next generation mixed exhaust aeroengines will be restricted to smaller liner segment lengths than the Silent Aircraft. This analysis suggests that scattering and hence liner order is likely to more important for these designs.

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Finite length tuning for low frequency lining design

Cited by 36 publications

References 1 publication

Finite Element-Integral Acoustic Simulation of JT15D Turbofan Engine

Finite Element-Integral Acoustic Simulation of JT15D Turbofan Engine

Main Fan Noise Mitigation Technologies in Turbofan Engines

Optimization of Annular and Cylindrical Liners for Mixed Exhaust Aeroengines

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