Mechanism underlying Kármán vortex street breakdown preceding secondary vortex street formation

Abstract

The Kármán street that develops behind a bluff body transforms in the far wake into a secondary vortex street of lower frequency and stronger vortices. Before this transformation, the primary street decays. This interesting phenomenon was investigated in a number of experimental and theoretical studies. Much of that work is devoted to studying the reasons for the formation of the secondary street and its frequency characteristics. Reasons for the decay of the primary street are not well understood. In this work, the mechanism underlying the breaking of the primary vortex street is studied. A qualitative explanation of this process is presented wherein a region of heightened density of the dipole moment forms. This region moves relative to the Kármán vortices so that its distance from the body remains constant. In this region, the Kármán vortex street collapses.