The objective of this study is to numerically simulate the experimentally observed merging process of vortex rings induced by acoustic excitation in a jet at a Reynolds number of 5000. The excited non-dimensional frequency (Strouhal number, St) was set to three values: 0.3, corresponding to the preferred mode frequency; 0.6, twice that frequency; and 1.2, at which four vortex rings merged in the experiment. The numerical results showed that at St = 0.3 and 0.6, no vortex rings merged, and the upstream vortex ring overtook the downstream one. At St = 1.2, two vortex rings merged, but the merging of four vortex rings was not observed, in contrast to the experimental results. Furthermore, the differences between vortex ring merging and overtaking were investigated by the induced velocity of a vortex ring.
HOSHI et al. (Wed,) studied this question.