The physical mechanism of symmetric vortex merger: A new viewpoint
Journal
Physics of Fluids
Journal Volume
17
Journal Issue
7
Pages
1-7
Date Issued
2005
Author(s)
Abstract
The physical mechanism of symmetric vortex merger is investigated in use of a resurrected core-spreading vortex method. By taking advantage of the Lagrangian characteristics of the vortex method, both Eulerian and Lagrangian flow structures are obtained and used to explore the cause of merger. The simulation results suggest that a complete merging process is as follows: the vortices deform first due to the mutually induced straining; the deformation results in elliptical vortices and an angle between the major axis of each elliptical vortex and the line joining the two vortices, which in turn cause an attraction of fluid particles from one vortex to the other; sheetlike vortex structures are thus formed; and finally the velocity field induced by these sheetlike structures readily pushes two vortex cores together. This study suggests that the competition between the self-induced rotation and mutual attraction of vortices governs the formation of the sheetlike structures, and consequently the merger. When the flow is viscous, the separation between vortices reduces and the mutual attraction increases with time by diffusion. As the mutual attraction dominates over the self-induced rotation, sheetlike structures are formed gradually and merger eventually occurs. The onset time of merger is thus found to depend not only on the initial separation but also on the Reynolds number. The former determines when the mutual attraction will become dominant and the latter controls the speed at which sheetlike structures grow.
Publisher
American Institute of Physics Inc.
Type
journal article