Michele Buzzicotti
University of Rome "Tor Vergata", Italy

Transition from 3D to 2D turbulence by Fourier space decimation

The transition between two and three dimensional flows is a central problem in turbulence. In this work we study this transition by changing the number of active degrees of freedom (DOF) in Fourier space without changing the aspect ratio of the 3D volume in real space. Following this approach we perform a decimation of DOF that smoothly interpolates from a fully 3D Fourier skeleton to a set of three mutually orthogonal 2D planes. The extreme decimation on a subset of DOF living only on one plane in Fourier space, i.e. kx=0, produces a 2D3C flow with the usual 2D inverse energy cascade. Relaxing the level of decimation allowing the DOF to live on a set of perpendicular planes allows the system to move towards a three dimensional behavior. To complete the transition to 3D turbulence we need to further activate a small percentage of DOF in the Fourier volume enhancing the coupling between the set of 2D planes. In this work we investigate the role of helicity in the energy transfer mechanisms. We observe that the contributions coming from the homohelical triads are always dominant in the formation of an inverse energy cascade.