Zigzag instability of the Karman vortex street in stratified and rotating fluids

Abstract : We investigate the three-dimensional stability of the Karman vortex street in a stratified and rotating fluid by means of an asymptotic theory for long-vertical wavelength and well-separated vortices. It is found that the Karman street with close rows is unstable to the zigzag instability when the fluid is strongly stratified independently of the background rotation. The zigzag instability bends the vortices with almost no internal deformation. The results are in excellent agreement with direct numerical stability analyses and may explain the formation of layers commonly observed in stratified flows.