Energy transfer in turbulence under rotation.

It is known that rapidly rotating turbulent flows are characterized by the emergence of simultaneous upscale and downscale energy transfer. Indeed, both numerics and experiments show the formation of large-scale anisotropic vortices together with the development of small-scale dissipative structures. However the organization of interactions leading to this complex dynamics remains unclear. Two different mechanisms are known to be able to transfer energy upscale in a turbulent flow. The first is characterized by 2-dimensional interactions amongst triads lying on the 2D3C/slow manifold, namely on the Fourier-plane perpendicular to the rotation axis. The second mechanism is 3-dimensional and consists of interactions between triads with the same sign of helicity (homo-chiral). Here, we present a detailed numerical study of rotating flows using a suite of high Reynolds number direct numerical simulations (DNS) within different parameter regimes to analyze both upscale and downscale cascade ranges. We find that the upscale cascade at wave-numbers close to the forcing scale is generated by increasingly dominant homo-chiral interactions which couple the 3-dimensional bulk and the 2D3C plane. This coupling produces an accumulation of energy in the 2D3C plane, which then transfers energy to smaller wave-numbers thanks to the 2-dimensional mechanism. In the forward cascade range, we find that the energy transfer is dominated by hetero-chiral triads and is dominated primarily by interaction within the fast manifold where $k_z\ne 0$. We further analyze the energy transfer in different regions in the real-space domain. In particular we distinguish high-strain from high-vorticity regions and we uncover that while the mean transfer is produced inside regions of strain, the rare but extreme events of energy transfer occur primarily inside the large-scale column vortices.