Radiated Pressure to Sound Power Ratio in Unflanged Circular Ducts

摘要

Theoretical expressions for sound radiation from a single incident duct mode, arriving at the open end of a semi-infinite circular unflanged duct with rigid walls, were used to obtain numerical results for the multimode far-field directivity factor. The modes are assumed to be incoherently excited, and a weighting model is adopted which includes equal power permode (above cutoff), and excitation by incoherent monopoles and axial dipoles uniformly distributed over a duct cross section as special cases. The findings have practical applications to sound power measurement from tall exhaust stacks.