Late dynamics of large-scale vortices in periodic two-dimensional flows

The inverse cascade in freely decaying two-dimensional flows with periodic boundary conditions will lead to a quasi-steady long-term system of vortices, which has not been well investigated in literature. By performing a series of direct numerical simulations, we focus on the late dynamics of these large-scale vortices. It is found that the theories of point vortices can be also approximately employed for both quadrate and hexagonal periodic conditions, however, in real flows the dynamics can switch among different motions, which differs from the theory of point vortices. It is observed as a special case of the wandering motions that the weakest vortex can migrate among different periods, with the other two vortices co-rotating. This phenomenon can be analogical to the physics of current flow. In addition, the merging procedure of large-scale vortices can be described by using the skewness of vorticity. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

In this study, the late dynamics of large-scale vortices in freely decaying two-dimensional flows with periodic boundary conditions have been investigated through direct numerical simulations. It was found that the theories of point vortices can be approximately applied to various periodic conditions, but the dynamics in real flows can switch among different motions. This study also observed a unique wandering motion phenomenon in which the weakest vortex can migrate among different periods while the other two vortices co-rotate, similar to the physics of current flow. Additionally, the merging process of large-scale vortices can be described using the skewness of vorticity.