Turbulence generation through an iterative cascade of the elliptical instability

Turbulent flows are notoriously difficult to study due to the lack of a mechanistic framework that encapsulates how vortices interact, break down, and form new vortices, driving the cascade of energy down to the dissipative scale. We demonstrate the existence of a novel mechanism in which two counter-rotating vortices violently collide and break down, leading to the rapid development of a turbulent energy cascade mediated by iterations of the elliptical instability. We probe the full 3D dynamics of this complex breakdown by conducting both experimental flow visualizations and numerical simulations of colliding vortex rings. The onset of the elliptical instability generates an ordered array of secondary vortex filaments that are perpendicular to the original cores. Adjacent secondary filaments counter-rotate and interact with each other. In the high-Reynolds number limit, we observe another iteration of this instability, whereby even smaller tertiary filaments form in the same manner. The energy spectrum of this breakdown exhibits Kolmogorov scaling, E(k) ~ k^(-5/3), a hallmark of homogeneous isotropic turbulence. Clear evidence of this mechanism of vortex generation has also been recently observed over many length scales in recent numerical simulations of forced turbulence.