Parametric resonance in a periodically perturbed von-Karman flow

We have performed numerical simulations of the kinematic induction equation in order to examine the dynamo efficiency of an axisymmetric von-Karman-like flow suct to time-dependent non-axisymmetric velocity perturbations. The numerical model is based on the setup of the French Von-Karman-Sodiuynamo and the flow measurements from a model water experiment conducted at the University of Navarra in Pamplona,ain. We find two distinct regimes of dynamo action that depend on the azimuthal drift of an (m=2) vortex like floerturbation. For comparatively slowly drifting vortices we observe a narrow window with enhanced growth-rates anddrift of the magnetic eigenmode that is synchronized with the flow perturbation drift. For larger vortex drift an abrupt transition to independently drifting magnetic eigenmode occurs and the field amplitude is modulated with twice the vortex driftequency. The sudden change between the resonant regime and the modulated regime is identified as an spectral exceonal point where eigenvalues and eigenfunctions of two previously independent modes collapse.