We consider rotating Rayleigh-B\'enard convection of a fluid with a Prandtl number of $Pr = 0.8$ in a cylindrical cell with an aspect ratio $\Gamma = 1/2$. Direct numerical simulations were performed for the Rayleigh number range $10^5 \leq Ra \leq 10^9$ and the inverse Rossby number range $0 \leq 1/Ro \leq 20$. We propose a method to capture regime transitions based on the decomposition of the velocity field into toroidal and poloidal parts. We identify four different regimes. First, a buoyancy dominated regime occurring as long as the toroidal energy $e_{ tor}$ is not affected by rotation and remains equal to that in the non-rotating case, $e^0_{ tor}$. Second, a rotation influenced regime, starting at rotation rates where $e_{ tor} > e^0_{ tor}$ and ending at a critical inverse Rossby number $1/Ro_{ cr}$ that is determined by the balance of the toroidal and poloidal energy, $e_{ tor} = e_{ pol}$. Third, a rotation dominated regime, where the toroidal energy $e_{ tor}$ is larger than both, $e_{ pol}$ and $e^0_{ tor}$. Fourth, a geostrophic turbulence regime for high rotation rates where the toroidal energy drops below the value of non-rotating convection.
Categories: physics.flu-dyn