Shear-layer acoustic radiation in an excited subsonic jet: experimental study |
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Authors: | Vincent Fleury Christophe Bailly Daniel Juvé |
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Institution: | Laboratoire de mécanique des fluides et d''acoustique, UMR CNRS 5509 & École centrale de Lyon, 36 avenue Guy de Collongue, 69134 Ecully cedex, France |
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Abstract: | The subharmonic acoustic radiation of a tone excited subsonic jet shear-layer has been investigated experimentally. Two jet velocities and were studied. For , the natural boundary-layer at the nozzle exit is laminar. When the perturbation is applied, the fluctuations of the first and the second subharmonics of the excitation frequency are detected in the shear-layer. In addition, the first subharmonic near pressure field along the spreading jet is constituted of two strong maxima of sinusoidal shape. The far-field directivity pattern displays two lobes separated by an extinction angle at around 85° from the jet axis. These observations follow the results of Bridges about the vortex pairing noise. On the other hand, for , the initial boundary-layer is transitional and only the first subharmonic is observed in the presence of the excitation. The near pressure field is of Gaussian shape in the jet periphery and the acoustic far-field is superdirective as observed by Laufer and Yen. The state of the initial shear-layer seems to be the key feature to distinguish these two different radiation patterns. To cite this article: V. Fleury et al., C. R. Mecanique 333 (2005). |
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Keywords: | Fluid mechanics Excited jet Subharmonic Pairing noise Superdirective radiation Mécanique des fluides Jet excité Sous-harmonique Bruit d'appariement Rayonnement superdirectif |
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