  Within the incompressible three-dimensional Euler equations, we study the
pancake-like high vorticity regions, which arise during the onset of developed
hydrodynamic turbulence. We show that these regions have an internal fine
structure consisting of three vortex layers. Such a layered structure, together
with the power law of self-similar evolution of the pancake, prevents
development of the Kelvin-Helmholtz instability.
