Sound radiation from a finite length unflanged circular duct with uniform axial flow. II. Computed radiation characteristics

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Abstract
Computed numerical results are presented for the sound radiation from a finite length unflanged hard wall circular duct with uniform axial flow both inside and outside the duct. The development of the necessary theory is outlined in part I of this report. In the present report, some of the finite duct effects are quantitatively presented for the simplest plane-wave excitation case, It is shown that the finite duct radiation problem exhibits two important physical phenomena. Firstly, length resonance effects lead to the creation of standing waves on either side of the source plane, in the duct interior. Secondly, the diffracted sound waves propagating from each duct end, interfere in the farfield producing a modified radiation directivity (relative to the semi-infinite duct radiation).

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