Switching phenomenon of conical vortices on various flat roofs

The conical vortices formed over a flat roof of cubic-type buildings have been considered to consist of a pair of vortices with mutually anti-angular velocity. However, the authors have recently found an interesting phenomenon that the conical vortices do not appear in the form of a pair of vortices but in the form of a single vortex. The phenomenon that when the conical vortex exists on one side it disappears on the other side is seen to be randomly repeated and therefore is called the ‘switching phenomenon*. In this paper, simultaneous multi-pressure measurements on cubic-type buildings and the POD analysis for the pressure measurements were performed along with the flow visualization technique effective for the vortical flow, to investigate and to clarify the mechanism of the switching phenomenon.