Rotating turbulence is central in many contexts, e.g. astrophysical, geophysical and industrial flows. A background rotation about a fixed axis introduces anisotropy in the turbulent dynamics through both linear and nonlinear mechanisms.
The flow regime can be characterized by two independent non-dimensional parameters, e.g. the Reynolds and Rossby numbers or, equivalently, the ratio of the integral scale to the Kolmogorov scale L/eta, and the ratio lZ/L, where lZ=sqrt(epsilon/Omega^3) is the Zeman scale, epsilon is the mean energy dissipation rate and Omega is the rotation rate. The Zeman scale is the scale l at which the inertial timescale (l^2/epsilon)^(1/3) equals the rotation timescale 1/Omega, and thus, if the Reynolds number is large, scales much larger than lZ are mainly affected by rotation while scales much smaller than lZ are dominated by the nonlinear dynamics and are expected to recover isotropy.

In this work, we perform high resolution pseudo-spectral direct numerical simulations of non-helical and helical forced rotating turbulence at high Reynolds number in a 3D periodic domain. The scale-dependence of anisotropy is characterized through energy and helicity direction-dependent spectra in the Fourier space. We focus on the low rotation regime, in which the large scale separation permits to study the anisotropic features of scales much smaller than the Zeman scale. We evidence the existence of a highly anisotropic small-wavenumber range and of a weakly anisotropic large-wavenumber range. Importantly, it is observed that the anisotropy level is still significant at the smallest resolved scales (although it decreases as the Rossby number increases), in contrast with recent numerical results, but in agreement with some experiments. Finally, we estimate the value of the threshold wavenumber between large-anisotropy wavenumbers and low-anisotropy wavenumbers, and provide a physical interpretation for it.