Two interacting vortex ring pairs and their sound generation

This paper reports a numerical study of the interactions of two coaxial thin vortex ring pairs and their far-field sound generation. Out of the different varieties of widely differing near-field vortex patterns, four basic types of interactions with their associated different degrees of amplification and attenuation of the far-field sound are identified. These four types are found to depend on the circulation ratio, radius ratio, separation ratio, and phase. The suppression of the interaction, caused by the introduction of the control vortex ring pair, results in the slight and moderate attenuation of sound. The initial and continuous rapid and intense interactions with either vortex rings of the control pair are responsible for the moderate amplification and intense amplification, respectively. This study, thus, establishes the importance of the understanding of the interaction dynamics and their patterns on the far-field sound generated. Except for the results of intense amplification, the results generally agree with coaxial jets of normal and inverted mean velocity profiles.