Bandpass filtering of the flow and sound was performed in order to gain further insight into the role of coherent structures in subsonic jet noise generation. The bandpass filtering procedure was conducted on the data obtained from a well-resolved large eddy simulation of sound radiation from an unheated, Mach 0.9 jet at Re_D = 400,000. Results from the bandpass filtering of the pressure field suggest two dominant mechanisms of sound radiation in unheated subsonic jets that can occur in all scales of turbulence. The first mechanism is the stretching and the distortion of coherent vortical structures. For large scale structures, i.e. low frequency radiation, this mechanism is dominant close to the termination of the potential core. This mechanism appears quadrupolar in nature, and is responsible for strong sound radiation at aft angles. The second sound generation mechanism appears to be the transverse vibration of the shear-layer interface within the ambient quiescent flow. This mechanism is believed to be responsible for sound radiation along the sideline directions.
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