Vortex ring with swirl: A numerical study

In this paper, we use a lattice Boltzmann method to study the effect of swirl on the dynamics of an isolated three-dimensional vortex ring in a viscous incompressible fluid. We focus on a fixed Reynolds number of 800 and vary swirl magnitude and vortex core size. Results show that increasing swirl for a fixed core size or increasing core size for a fixed swirl causes vortex ring to slow down or even travel backward initially. A simplified physical explanation for this dynamic behavior is proposed. Our results further show that while a weak swirl causes vortex filaments to undergo helical winding, a sufficiently strong swirl transforms these windings into convoluted three-dimensional vortex structure with vortex loops trailing behind it. Each of these vortex loops may reconnect with itself, through the process of vortex reconnection, to form a ringlet. (C) 2010 American Institute of Physics. [doi:10.1063/1.3478976]