Acoustic performance of inlet suppressors on an engine generating a single mode

Heidelberg, Laurence J.; Rice, E. J.; Homyak, L.

doi:10.2514/6.1981-1965

Cited by 9 publications

(21 citation statements)

References 3 publications

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“…The attenuation is relatively large at mode cut-on, and this is seen both in the measured and the FEM results. It had been noted in a previous study by Heidelberg et al 4 that the performance of a liner improves at mode cut-on. This is felt to be due to the fact that the axial particle velocity approaches zero at mode cut-on and the liner has more time to extract energy from the wave as it passes over the liner.…”

Section: A Plane Wave and Higher Order Mode Excitation In The Duct Wmentioning

confidence: 99%

“…Thus the finite element results are therefore post-processed to determine the axial acoustic particle velocity. The acoustic pressure and axial particle velocity are coupled, as shown in Equation (4). The finite element solution in the downstream section, p m (x,y,z d ), is expanded into rigid wall duct modes as in Equation (1) and the mode amplitudes in the section are extracted numerically.…”

Section: A Mnmentioning

confidence: 99%

“…Heidelberg, et al 4 investigated the effect that mode shape has on acoustic performance of a locally reacting liner.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of Liner Characteristics in the NASA Langley Curved Duct Test Rig

Gerhold

Brown

Watson

et al. 2007

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

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The Curved Duct Test Rig (CDTR), which is designed to investigate propagation of sound in a duct with flow, has been developed at NASA Langley Research Center. The duct incorporates an adaptive control system to generate a tone in the duct at a specific frequency with a target Sound Pressure Level and a target mode shape. The size of the duct, the ability to isolate higher order modes, and the ability to modify the duct configuration make this rig unique among experimental duct acoustics facilities. An experiment is described in which the facility performance is evaluated by measuring the sound attenuation by a sample duct liner. The liner sample comprises one wall of the liner test section. Sound in tones from 500 to 2400 Hz, with modes that are parallel to the liner surface of order 0 to 5, and that are normal to the liner surface of order 0 to 2, can be generated incident on the liner test section. Tests are performed in which sound is generated without axial flow in the duct and with flow at a Mach number of 0.275. The attenuation of the liner is determined by comparing the sound power in a hard wall section downstream of the liner test section to the sound power in a hard wall section upstream of the liner test section. These experimentally determined attenuations are compared to numerically determined attenuations calculated by means of a finite element analysis code. The code incorporates liner impedance values educed from measured data from the NASA Langley Grazing Incidence Tube, a test rig that is used for investigating liner performance with flow and with (0,0) mode incident grazing. The analytical and experimental results compare favorably, indicating the validity of the finite element method and demonstrating that finite element prediction tools can be used together with experiment to characterize the liner attenuation.

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Section: A Plane Wave and Higher Order Mode Excitation In The Duct Wmentioning

confidence: 99%

Section: A Mnmentioning

confidence: 99%

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Investigation of Liner Characteristics in the NASA Langley Curved Duct Test Rig

Gerhold

Brown

Watson

et al. 2007

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

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“…To determine far field directivity, it is, therefore, necessary to extend the numerical solution to the far field. Currently, the Kirchhoff method and the Ffowcs Williams and Hawkings method 36 (see also Pilon and Lyrintzis 37 and Lyrintzis 38 ) are the two most popular methods for extending near field results to the far field. To use these methods, one encloses the near field by a matching surface.…”

Section: Extension To the Far Fieldmentioning

confidence: 99%

Physics of Acoustic Radiation from Jet Engine Inlets

Tam

Parrish

Envia

et al. 2012

18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)

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Numerical simulations of acoustic radiation from a jet engine inlet are performed using advanced computational aeroacoustics (CAA) algorithms and high-quality numerical boundary treatments. As a model of modern commercial jet engine inlets, the inlet geometry of the NASA Source Diagnostic Test (SDT) is used. Fan noise consists of tones and broadband sound. This investigation considers the radiation of tones associated with upstream propagating duct modes. The primary objective is to identify the dominant physical processes that determine the directivity of the radiated sound. Two such processes have been identified. They are acoustic diffraction and refraction. Diffraction is the natural tendency for an acoustic wave to follow a curved solid surface as it propagates. Refraction is the turning of the direction of propagation of sound waves by mean flow gradients. Parametric studies on the changes in the directivity of radiated sound due to variations in forward flight Mach number and duct mode frequency, azimuthal mode number, and radial mode number are carried out. It is found there is a significant difference in directivity for the radiation of the same duct mode from an engine inlet when operating in static condition and in forward flight. It will be shown that the large change in directivity is the result of the combined effects of diffraction and refraction.

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“…Various methods to measure noise in the engine and decompose it into the modal structure have been developed; including a rotating rake of microphones 6 , surface-mounted microphones in the inlet 7 , or a duct extension. 8 Heidelberg, et al 9 investigated the effect that modeshape has on acoustic performance of a liner. They found that the liner performance improves significantly near a mode cut on.…”

Section: Introductionmentioning

confidence: 99%

Development of an Experimental Rig for Investigation of Higher Order Modes in Ducts

Gerhold¹,

Cabell

Brown

2006

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

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Continued progress to reduce fan noise emission from high bypass ratio engine ducts in aircraft increasingly relies on accurate description of the sound propagation in the duct. A project has been undertaken at NASA Langley Research Center to investigate the propagation of higher order modes in ducts with flow. This is a two-pronged approach, including development of analytic models (the subject of a separate paper) and installation of a laboratory-quality test rig. The purposes of the rig are to validate the analytical models and to evaluate novel duct acoustic liner concepts, both passive and active. The dimensions of the experimental rig test section scale to between 25% and 50% of the aft bypass ducts of most modern engines. The duct is of rectangular cross section so as to provide flexibility to design and fabricate test duct liner samples. The test section can accommodate flow paths that are straight through or offset from inlet to discharge, the latter design allowing investigation of the effect of curvature on sound propagation and duct liner performance. The maximum air flow rate through the duct is Mach 0.3. Sound in the duct is generated by an array of 16 high-intensity acoustic drivers. The signals to the loudspeaker array are generated by a multi-input/multi-output feedforward control system that has been developed for this project. The sound is sampled by arrays of flush-mounted microphones and a modal decomposition is performed at the frequency of sound generation. The data acquisition system consists of two arrays of flush-mounted microphones, one upstream of the test section and one downstream. The data are used to determine parameters such as the overall insertion loss of the test section treatment as well as the effect of the treatment on a modal basis such as mode scattering. The methodology used for modal decomposition is described, as is a description of the mode generation control system. Data are presented which demonstrate the performance of the controller to generate the desired mode while suppressing all other cut on modes in the duct.

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Acoustic performance of inlet suppressors on an engine generating a single mode

Cited by 9 publications

References 3 publications

Investigation of Liner Characteristics in the NASA Langley Curved Duct Test Rig

Investigation of Liner Characteristics in the NASA Langley Curved Duct Test Rig

Physics of Acoustic Radiation from Jet Engine Inlets

Development of an Experimental Rig for Investigation of Higher Order Modes in Ducts

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