A FINITE-LENGTH INSTABILITY OF VORTEX TUBES

We show that vortex tubes of finite length have an instability which d estroys the vorticity structure quickly. Axial flows develop within th e core of the vortex structure, directed inwards from both ends of the vortex tube. The converging axial flows cause the core at the midpoin t in length of the vortex tube to expand rapidly, disrupting the vorte x structure. Examples of this instability are shown by simulation, and the properties of the instability are derived. In order for the conce ntrated vorticity structures of turbulence to survive this instability they must be embedded in an external how which compensates for the se lf-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.