ANALYTICAL AND NUMERICAL STUDY OF A SWIRLING SUBMERGED JET FLOW

摘要

The present study is conducted to investigate the details and characteristics of swirling submerged jets when transferred into a system of helical vortices downstream in a bathtub-like flow. Both analytical and numerical results are presented. In the analytical solution, upstream flow is considered to be two-dimensional with piecewise-constant vorticity profile. The instability of such a flow leads to the formation of two-dimensional dipolar or tripolar vortical structures. It is shown that the size of the vortexless annular area inside the initial vortex is a critical parameter in the two dipolar unstable or tripolar stable structure formations, and that such tripolar flow transforms downstream to a three-dimensional steady helical vortex system, which rotates as a whole and propagates in the downstream direction. The mechanism of screwing vortex filaments into a steady system of helical vortices is also presented. The numerical simulations also confirm the initiation and generation of dipolar vortex structures.