Azimuthal Decomposition of the Noise of a Dual-Stream Coaxial Jet

Azimuthal decomposition was used to study the azimuthal composition of noise of a jet issuing from a coaxial nozzle. Various combinations of the velocities of the core and bypass jets are considered. The features observed in the spectral characteristics and in the shapes of the directivity patterns of individual azimuthal modes are analyzed, in particular, the excess noise of a coaxial jet over the noise of an equivalent fully mixed jet when there is a significant difference in velocities in the outer and inner ducts. It is also shown that the difference between them occurs in all three azimuthal modes, and the main problem for noise simulation is the coaxial jet transition zone.