A finite-length instability of vortex tubes

We show that vortex tubes of finite length have an instability which destroys the vorticity structure quickly. Axial flows develop within the core of the vortex structure, directed inwards from both ends of the vortex tube. The converging axial flows cause the core at the midpoint in length of the vortex tube to expand rapidly, disrupting the vortex structure. Examples of this instability are shown by simulation, and the properties of the instability are derived. In order for the concentrated vorticity structures of turbulence to survive this instability they must be embedded in an external how which compensates for the self-generated axial flow. This emphasizes the importance of considering the environment of the vortex structures and not just the structures in isolation. (C) Elsevier, Paris.