Jet Noise Containing Discrete Frequency : 2nd Report, Effect of Structure and Behavior of Vortex Ring

Abstract

The effect of the structure and behavior of vortex rings on jet noise containing discrete frequency has been studied by digital image processing. In particular, the behavior of a series of vortex rings released from a nozzle with divergent exit angle was clarified by a high-speed video camera including Schlieren systems. The structures of vortex rings were classified into the following phenomena : chasing phenomenon in which a leading vortex ring was chased by a released vortex ring, merging phenomenon in which a released vortex ring merged after passing-through to a leading vortex ring, and rolling up phenomenon in which the main flow was rapidly rolled up after contraction. It was found that the discrete frequency was affected considerably by the vortex structure and behavior, and the characteristic frequency distributions for the above phenomena were presented. Furthermore, in spite of considerably lower pressure, violent discrete frequency and screech noise such as that generated by a supersonic jet were generated.