Abstract
In this report, it was discussed by the digital image processing that the characteristics of the discrete frequency noise for subsonic jets were closely related to the structure and behavior of vortex rings. The vortex rings released from nozzle with exit divergent angle, were visualized by Schlieren method or a high-speed video camera included its system. It was clarified that the interaction of vortex rings were classified into phenomena of chasing, merging and rolling up and so on, and those phenomena had characteristic frequency distributions of noise respectively.
