Transitional and weakly turbulent flow in a rotating magnetic field

The early stage of the turbulent flow driven by a rotating magnetic field is studied via direct numerical simulations and electric potential measurements for the case of a cyindrical geometry. The numerical results show that the undisturbed flow remains stable up to the linear stability limit, wheras small perturbations may initiate nonlinear transition at subcritical Taylor numbers. The observed instabilities occur randomly as isolated pairs of Taylor-Görtler vortices, which grow from spots to long tubes until they are dissipated in the lid boundary layers. At 7.5 times the critical Taylor number, the flow is governed by large-scale 3D fluctuations and may be characterized as weakly turbulent. Taylor-Görtler vortices provide the major turbulence mechanism, apart from oscillations of the rotation axis. As the vortices tend to align with the azimuthal direction, they result in a locally two-dimensional turbulence pattern.