| 摘要 |
PROBLEM TO BE SOLVED: To provide a measurement system for correctly obtaining the position of the acoustic source of jet noise (screech) produced by a supersonic jet stream. SOLUTION: High-speed sampling is performed while shifting a measurement point by the use of a high-speed optical sensor in a schlieren-optical system. Changes in values acquired by the sampling are produced as a result of bending of an optical path by a density gradient produced in an arc shape from the center of the jet stream. Discrete Fourier transform is applied to these values, to decompose the noise into frequency components constituting it. Subsequently, Abel conversion is applied concerning data belonging to a specific frequency to obtain a density gradient in a radial direction from the center of the jet stream. The position of the acoustic source and the state of the stream can be acquired in detail by visualizing the obtained density gradient by graphic display. COPYRIGHT: (C)2009,JPO&INPIT
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