Are there two regimes in strongly rotating turbulence?

We describe numerical experiments of freely decaying, rapidly rotating turbulence in which the Rossby number varies from Ro = O(1) down to Ro similar to 0.02. Our central premise is that there exists two distinct dynamical regimes; one for Ro > 0.3 -> 0.4, which is typical of most laboratory experiments, and another corresponding to Ro < 0.3, which covers most previous numerical studies. The case of Ro > 0.3. 0.4 is reported in Baqui and Davidson [A phenomenological theory of rotating turbulence, Phys. Fluids 27, 025107 (2015)] and is characterised by: (i) a growth of the parallel integral scale according to l(parallel to) similar to l(perpendicular to)Omega t; (ii) a dissipation law which is quite different from that predicted by weak-turbulence theories, specifically epsilon = beta u(3)/l(parallel to) where the pre-factor beta is a constant of order unity; and (iii) an inertial-range energy spectrum for both the parallel and perpendicular wavenumbers which scales as k(-5/3), a scaling that has nothing to do with Kolmogorov's law in non-rotating turbulence. (Here, l(parallel to) is the integral length-scale parallel to the rotation vector Omega, l(perpendicular to) the integral length-scale perpendicular to Omega, u the integral scale velocity, and epsilon the viscous dissipation rate per unit mass.) By contrast, in the low-Ro regime, we find that l(parallel to) similar to l(perpendicular to)Omega t is replaced by l(parallel to) similar to ut and there is no power-law scaling of the inertial range energy spectrum. While the dissipation law epsilon = beta u(3)/l(parallel to) continues to hold at low Ro, at least approximately, the value of beta now depends on Ro. It appears, therefore, that the dynamics of these two regimes are very different, and this may help explain why experimentalists and theoreticians sometimes present rather different interpretations of rotating turbulence. (C) 2016 AIP Publishing LLC.