An Active Anechoic Termination for Low Frequencies with Mean Flow
This paper deals with the behavior of an active anechoic termination for low frequencies (<150 Hz) in the presence of mean flow. The auxiliary source is an oscillating valve positioned within the flow which can be considered as an acoustic source in series with a primary source. This system was previously used to eliminate flow periodic fluctuations in exhaust from reciprocating engines. The modeling (briefly recalled here) is based on the propagation of plane waves in flow, the principle of the superposition of linear acoustics, and electroacoustic analogies. It is first shown that the reflection coefficient can be minimized for a uniform duct in the case of a fixed valve positioned in incidence. It is then demonstrated that the reflection coefficient can be controlled by oscillating the valve to provide an active anechoic termination. This active method allows the passive influence of the valve to be reduced in an acoustic circuit through limitation of head-loss. The theoretical study was validated by an experimental application confirming the viability of this low-frequency termination. A 5% lower reflection coefficient was obtained from 40 to 110 Hz, with a Mach number of around 0.05.
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Document Type: Research Article
Publication date: 1997-01-01
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- Acta Acustica united with Acustica, published together with the European Acoustics Association (EAA), is an international, peer-reviewed journal on acoustics. It publishes original articles on all subjects in the field of acoustics, such as general linear acoustics, nonlinear acoustics, macrosonics, flow acoustics, atmospheric sound, underwater sound, ultrasonics, physical acoustics, structural acoustics, noise control, active control, environmental noise, building acoustics, room acoustics, acoustic materials, acoustic signal processing, computational and numerical acoustics, hearing, audiology and psychoacoustics, speech, musical acoustics, electroacoustics, auditory quality of systems. It reports on original scientific research in acoustics and on engineering applications. The journal considers scientific papers, technical and applied papers, book reviews, short communications, doctoral thesis abstracts, etc. In irregular intervals also special issues and review articles are published.
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