Kinetic-magnetic energy exchanges in rotating magnetohydrodynamic turbulence

Abstract

ABSTRACTWe use direct numerical simulations to study the dynamics of incompressible homogeneous turbulence subjected to a uniform magnetic field in a rotating frame with rotation vector . We consider two cases: and . The initial state is homogeneous isotropic hydrodynamic turbulence with Reynolds number The magnetic Prandtl number and the Elsasser number , 0.9 or 2. For both the cases and the total energy decays as for and 0.9, and as for . In the spectral range 2 < k < 20, the kinetic energy spectrum scales as where p increases with time (). This scaling is similar to that observed in quasi-static MHD. The two rotating MHD flow cases differ mainly in how kinetic and magnetic fluctuations exchange energy, with a mechanism mostly driven by the dynamics of the spectral buffer layer around . At the inertial and Alfvén waves frequencies vanish when , but only the inertial waves frequency vanishes when . When , rotation results in an increased reduction of magnetic fluctuations generation. In terms of anisotropy, we show that the elongated structures occurring in rapidly non-magnetised rotating flows are distorted or inhibited for , and weakened for .