Two interacting vortex ring pairs and their sound generation

This paper reports a numerical study of the interactions of two coaxial thi n vortex ring pairs and their far-field sound generation. Out of the differ ent varieties of widely differing near-field vortex patterns, four basic ty pes of interactions with their associated different degrees of amplificatio n and attenuation of the far-field sound are identified. These four types a re 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 attenu ation of sound. The initial and continuous rapid and intense interactions w ith either vortex rings of the control pair are responsible for the moderat e 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 result s of intense amplification, the results generally agree with coaxial jets o f normal and inverted mean velocity profiles.