This study describes the methods and results of a new approach toward positively iden¬tifying the apparent location and strength of the sound source in a subsonic jet The Green's function technique is applied to regenerate the three-dimensional distribution of the acoustic far field from measured data on a two-dimensional plane The apparent sound-source loca¬tion is also determined by using geometrical ray acoustics The results revealed a number of features of the subsonic jet noise mechanisms. They show that the apparent sound source is highly localized within the jet flow and that the spontaneous noise emission from such a compact source volume is in the fashion of a narrow beam with random directions These observable properties of the sound field offer the basis for a beam pattern concept of sub¬sonic jet noise radiation This study not only provides the immediate benefit of new insight into the mechanisms of subsonic noise radiation but also verifies a powerful and accurate technique of aerodynamic noise measurements This technique is expected to have impor¬tant applications in the development of jet noise reduction technology.
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