Separated Rows structure of vortex streets behind triangular objects

TL;DR

This paper investigates two distinct vortex street structures behind triangular objects, revealing conditions for the exotic separated rows structure and analyzing their stability and decay mechanisms.

Contribution

It introduces the separated rows vortex structure in a soap film setup and identifies boundary layer thickness as a key factor for its formation.

Findings

Separated rows structure appears when boundary layer thickness is less than 40% of separation distance.

Conventional mushroom structure decays due to viscosity.

Separated rows structure is hydrodynamically unstable.

Abstract

We discuss two distinct spatial structures of vortex streets. The `conventional mushroom' structure is commonly discuss in many experimental studies, but the exotic `separated rows' structure is characterized by a thin irrotational fluid between two rows of vortices. In a two-dimensional soap film channel, we generated the exotic vortex arrangement by using triangular objects. This setup allows us to vary the thickness of boundary layers and their separation distance independently. We find that the separated rows structure appears only when the boundary layer thickness is less than 40% of the separation distance. We also discuss two physical mechanisms of the breakdown of vortex structures. The conventional mushroom structure decays due to the action of viscosity, and the separated rows structure decays because its arrangement is hydrodynamically unstable.