Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 13 of 13 for “"acoustic liners"”.
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Numerical investigation of slat noise attenuation using acoustic liners
… of attenuating slat noise using absorptive acoustic liners in the slat/main element gap is explored using a time domain computational aeroacoustic (CAA) technique. The aims of the development and application of the computational method are to reveal the mechanism of the slat noise generation …
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Direct numerical investigation and reduced-order modeling of 3-D honeycomb acoustic liners
Single degree-of-freedom conventional acoustic liners are widely installed in jet engines to reduce internal engine noise. They work by converting acoustic energy into vorticity-bound fluctuations. Despite being widely used, effective design-stage models of acoustic liners placed in high sound …
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Damping Parameter Study of a Perforated Plate with Bias Flow
… is the dynamic instability also known as thermo-acoustic instability. Concerns with this ongoing problem have grown with the introduction of Lean Premixed Combustion (LPC) systems developed to address the environmental concerns associated with the conventional combustion systems.</p><p>The most …
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Investigating the Feasibility and Stability for Modeling Acoustic Wave Scattering Using a Time-Domain Boundary Integral Equation with Impedance Boundary Condition
… objective in the field of computational aeroacoustics. When designing next generation quiet and environmentally friendly aircraft, it is important to be able to accurately and efficiently predict the acoustic scattering by an aircraft body from a given noise source. Acoustic liners are an …
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Improvement In Acoustic Liner Attenuation In Turbofan Engines By Means Of Plasma Synthetic Jet Actuator
… to reduce noise emissions. Turbofan engine acoustic liners are efficient attenuators of engine noise. Plasma actuators have been used as flow control devices in other settings and will now be studied as an enhancement for acoustic liners. A plasma actuator can excite oscillatory flow or a …
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Theoretical Modeling with Validation of a Combined HQ-Liner System for Turbofan Engine Noise Control
The combination of traditional passive acoustic liners with Herschel-Quincke (HQ) waveguides is proposed in this work as a device for Turbofan Engine Noise Control. The approach consists of installing circumferential arrays of HQ tubes on the lined sector of the inlet of a turbofan engine. A …
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Advanced Trailing Edge Blowing Concepts for Fan Noise Control: Experimental Validation
… spectral shape increases the performance of acoustic liners used in conjunction with trailing edge blowing. This thesis presents numerical predictions performed to estimate the sound power reductions due to these concepts, as well as experimental results taken on the ANCF rig at NASA Glenn …
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Acoustic and thermal packaging of small gas turbines for portable power
… gas turbine engine poses major challenges in the acoustic treatment that is required to attenuate the broadband and tonal noise of the high-speed turbomachinery. The challenge in the thermal management is the relatively large required cooling mass flow and the short flow mixing length, constrained …
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Acoustic optimisation and prediction of sound propagation in turbofan engine ducts
… optimisation of noise attenuation<br/>by using acoustic liners. A commercial FE/IE code ACTRAN/TM is used<br/>within two shell programs; B-induct for bypass ducts and ANPRORAD for intake ducts.<br/><br/>An automated liner impedance capability has been demonstrated by exploiting an …
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Experiments and Impedance Modeling of Liners Including The Effect of Bias Flow
The study of normal impedance of perforated plate acoustic liners including the effect of bias flow was studied. Two impedance models were developed, by modeling the internal flows of perforate orifices as infinite tubes with the inclusion of end corrections to handle finite length effects. These …
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Broadband Acoustic Liner Optimization Study Using Novel Poro-elastic Materials
… aircraft engine noise, there is need for acoustic liner configurations that target broadband performance. This thesis experimentally and analytically investigates passive noise control methods to improve broadband frequency attenuation through various acoustic liner designs. The inclusion …
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Prediction and control of sound propagation in turbofan engine bypass ducts
… research into the propagation of sound in acoustically lined ducts<br/>with flow. The motivation for this work is the requirement to predict the sound attenuation of<br/>acoustic liners in the bypass duct of modern turbofan aeroengines. The liners provide the most<br/>effective means with …