Exotic vortex streets created behind triangular objects

We discuss two distinct spatial structures of von Karman vortex streets. The ‘conventional mushroom’ structure is commonly discussed in many experimental studies, but the exotic ‘separated rows’ structure is characterized by a thin irrotational fluid between two rows of vortices. In our experimental studies in two-dimensional soap films, we show that these spatial structures are determined by the ratio between the boundary layers and their separation distance. The spatial structures then determines the physical mechanism for the decay of vortex streets. We find that the conventional mushroom structure decays due to the mixing, and the separated rows structure decays because its arrangement is hydrodynamically unstable.