On the Coherence of the Sound Field in a Circular Duct with Uniform Mean Flow

ISSN： 0022-460X

Source： Journal of Sound and Vibration, Vol.190, Iss.2, 1996-02, pp. : 261-271

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Abstract

The sound pressure generated by a point mass monopole with arbitrary time dependence in a circular duct with uniform mean flow has been derived in the time domain. In a further step, the cross-correlation function and the cross-spectral density of the sound pressure between two microphone positions have been calculated. It is found that the coherence function of the sound pressure generated by a single source is unity. This is different when the sound pressure is generated by two different uncorrelated sources. Then the coherence function can be smaller than unity, indicating that the sound field in this case is not completely coherent. Furthermore, a method has been proposed to check whether or not the sound field in a circular duct is completely coherent. The theoretical results have been verified by measurements in a circular duct without mean flow.