Acoustic Treatment Design Scaling Methods. Volume 1; Overview, Results, and Recommendations
Acoustic Treatment Design Scaling Methods. Volume 1; Overview, Results, and Recommendations

Author: National Aeronautics and Space Administration (NASA)

Publisher: Createspace Independent Publishing Platform

Published: 2018-06-15

Total Pages: 40

ISBN-13: 9781721182558

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Scale model fan rigs that simulate new generation ultra-high-bypass engines at about 1/5-scale are achieving increased importance as development vehicles for the design of low-noise aircraft engines. Testing at small scale allows the tests to be performed in existing anechoic wind tunnels, which provides an accurate simulation of the important effects of aircraft forward motion on the noise generation. The ability to design, build, and test miniaturized acoustic treatment panels on scale model fan rigs representative of the fullscale engine provides not only a cost-savings, but an opportunity to optimize the treatment by allowing tests of different designs. The primary objective of this study was to develop methods that will allow scale model fan rigs to be successfully used as acoustic treatment design tools. The study focuses on finding methods to extend the upper limit of the frequency range of impedance prediction models and acoustic impedance measurement methods for subscale treatment liner designs, and confirm the predictions by correlation with measured data. This phase of the program had as a goal doubling the upper limit of impedance measurement from 6 kHz to 12 kHz. The program utilizes combined analytical and experimental methods to achieve the objectives. Kraft, R. E. and Yu, J. Glenn Research Center; Langley Research Center NASA/CR-1999-209120/VOL1, NAS 1.26:209120/VOL1

Acoustic Treatment Design Scaling Methods. Volume 4; Numerical Simulation of the Nonlinear Acoustic Impedance of a Perforated Plate Single-Degree-Of-Freedom Resonator Using a Time-Domain Finite Difference Method
Acoustic Treatment Design Scaling Methods. Volume 4; Numerical Simulation of the Nonlinear Acoustic Impedance of a Perforated Plate Single-Degree-Of-Freedom Resonator Using a Time-Domain Finite Difference Method

Author: National Aeronautics and Space Administration (NASA)

Publisher: Createspace Independent Publishing Platform

Published: 2018-08-27

Total Pages: 50

ISBN-13: 9781726170833

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Single-degree-of-freedom resonators consisting of honeycomb cells covered by perforated facesheets are widely used as acoustic noise suppression liners in aircraft engine ducts. The acoustic resistance and mass reactance of such liners are known to vary with the intensity of the sound incident upon the panel. Since the pressure drop across a perforated liner facesheet increases quadratically with the flow velocity through the facesheet, this is known as the nonlinear resistance effect. In the past, two different empirical frequency domain models have been used to predict the Sound Pressure Level effect of the incident wave on the perforated liner impedance, one that uses the incident particle velocity in isolated narrowbands, and one that models the particle velocity as the overall velocity. In the absence of grazing flow, neither frequency domain model is entirely accurate in predicting the nonlinear effect that is measured for typical perforated sheets. The time domain model is developed in an attempt to understand and improve the model for the effect of spectral shape and amplitude of multi-frequency incident sound pressure on the liner impedance. A computer code for the time-domain finite difference model is developed and predictions using the models are compared to current frequency-domain models.Kraft, R. E.Glenn Research Center; Langley Research CenterDEGREES OF FREEDOM; NOISE REDUCTION; PRESSURE EFFECTS; SOUND INTENSITY; HONEYCOMB STRUCTURES; AIRCRAFT ENGINES; GRAZING FLOW; NOISE (SOUND); FLOW VELOCITY; MATHEMATICAL MODELS; RESONATORS; SOUND PRESSURE; NONLINEARITY...

Civil Jet Aircraft Design
Civil Jet Aircraft Design

Author: Lloyd R. Jenkinson

Publisher: Elsevier Limited

Published: 1999

Total Pages: 440

ISBN-13:

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There is an increasing emphasis in aeronautical engineering on design. Concentrating on large scale commercial jet aircraft, this textbook reflects areas of growth in the aircraft industry and the procedures and practices of civil aviation design.

Acoustic Characteristics of Perforated Dissipative and Hybrid Silencers
Acoustic Characteristics of Perforated Dissipative and Hybrid Silencers

Author: Iljae Lee

Publisher:

Published: 2005

Total Pages:

ISBN-13:

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Abstract: Acoustic characteristics of silencers filled with fibrous material (hence dissipative) are investigated. Following a theoretical and experimental analysis of a single-pass, perforated, dissipative concentric silencer, the study is extended to a hybrid silencer designed by combining dissipative and reflective (Helmholtz resonator) components. The ability to model these silencers relies heavily on the understanding of the acoustic behavior of the fibrous material and the perforations. Therefore, the present study has developed two experimental setups to measure: (a) the complex characteristic impedance and the wavenumber of the fibrous material with varying filling density and texturization conditions, and (b) the acoustic impedance of perforations in contact with the fibrous material, and with and without the mean flow. New empirical expressions are then provided for the acoustic impedance of perforations with varying porosity, hole diameter, wall thickness, mean flow rate, and the fiber characteristics. The experimental results illustrate that the presence of absorbent significantly increases both the resistance and reactance of the perforation impedance. The addition of mean flow is also shown in general to increase the resistance, while decreasing the reactance particularly at low porosities. The empirical expressions for the fiber acoustic properties and the perforation impedance are then integrated into the predictions of transmission loss. These predictions are based primarily on a three-dimensional boundary element method (BEM) developed in the present study, due to its ability to treat silencers with complex internals, in addition to one- and two-dimensional analytical approaches also introduced. Comparisons of predictions with the acoustic attenuation experiments support the proposed relationships for the properties of fibrous material and the perforation impedance. The influence of the internal geometry modifications of dissipative silencers, such as baffles and extended inlet/outlet, and the impact of connecting duct length between a pair of silencers, are investigated with BEM. Hence, the contributions of the present study include the development of methodologies for the measurement of acoustic properties of the fibrous material and the impedance of perforations, particularly in contact with the absorbent along with the resulting empirical expressions, thereby assisting towards analytical and computational design tools for the dissipative and hybrid silencers.