Measurement of the Acoustic Velocity by Laser Doppler Anemometry
Abstract:This study concerns the use of Laser Doppler Anemometry (L.D.A.) for direct measurement of the amplitude and frequency of the acoustic velocity in air within a standing wave pipe. This technique is uncommon in acoustics, although it allows important possibilities of velocity measurements in difficult situations in comparison to usual techniques. The major advantages of this velocity measurement technique are its non-intrusiveness and capacity to compensate for inversions of instantaneous velocity. However, non-uniform time interval sampling of the signal delivered by this measurement procedure requires appropriate data processing. In fact, random sampling depends directly on the presence of microparticles contained within the fluid and used as a tracer. The paper concerns also the data-processing techniques we used in this field. Our study confirms that L.D.A. is suitable for direct measurement of the acoustic velocity. It is shown that data derived from the L.D.A. measurement system and sampled in a random manner require appropriate processing, with special attention to the calculation procedures used. The amplitude spectrum calculation used here provides the frequency and amplitude of the velocity of the standing acoustic wave superimposed on mean flow, which was controlled to maintain the homogenization of microparticle sowing of the fluid studied. The presentation of the processing procedure used includes an analysis of the different parameters capable of influencing the technique of direct measurement of instantaneous velocity. Our experimental results showed that the restoration of instantaneous changes in flow velocity was also of excellent quality with this technique. Pressure measurement values were comparable, indicating the feasibility of applying this L.D.A. technique elsewhere, notably at the pipe ends.
Document Type: Research Article
Publication date: November 1, 1997
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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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