Dynamo action driven by a periodically perturbed Beltrami-flow.

We apply kinematic simulations of the induction equations in order to examine the ability of a Beltrami flow (with curl(V) ~V) generating dynamo action. In the basic state we find a surprisingly complex behavior of the leading azimuthal modes that have a wavenumber up to m=3. Depending on the relation of poloidal to toroidal flow the eigenmodes show slow amplitude modulations and a azimuthal drift of the field pattern.

In a more complex model we add a non-axisymmetric time-dependent flow perturbation. In extension of a previous study we change the (azimuthal) pattern and amplitude of the perturbation flow. Consequently, the magnetic field growth rates are enhanced when the frequency of the perturbation is in the appropriate regime. We find small windows of perturbation frequencies with strong enhancement of the growth rates as well as broader regimes for rather fast drifting perturbations when the perturbation amplitude is sufficient to alter structure of the basic axisymmetric flow.

The effect may be relevant for forthcoming dynamo experiments conducted in Madison or in the precession dynamo experiment at HZDR, where, however, the basic flow will look quite different.