Direct Computation of Sound Generation by the Symmetric Vortex Merger

It is significant to understand the sound-generating processes in the merging of two co-rotating vortex pair. In this paper, we use CCS scheme to direct numerical compute the nearfield dynamics and far-field acoustics of co-rotating vortex pair. The results show that the acoustic source is a rotating quadrupole, and the acoustic waves is a double spiral cylindrical pattern. The sound pressure increase in both frequency and amplitude towards merger. The acoustic wave has a peak in amplitude at the moment of vortex merger. The sound pressure shows an increase in frequency and a decrease in amplitude after vortex merger.