Vortex stretching

In fluid dynamics, vortex stretching is the lengthening of vortices in three-dimensional fluid flow, associated with a corresponding increase of the component of vorticity in the stretching direction—due to the conservation of angular momentum.

For example, vorticity transport in an incompressible inviscid flow is governed by where D/Dt is the material derivative.

In general, in turbulence fluid elements are more lengthened than squeezed, on average.

For incompressible flow—due to volume conservation of fluid elements—the lengthening implies thinning of the fluid elements in the directions perpendicular to the stretching direction.

Finally, at the small scales of the order of the Kolmogorov microscales, the turbulence kinetic energy is dissipated into heat through the action of molecular viscosity.