  Dynamo action owing to helically forced turbulence and large-scale shear is
studied using direct numerical simulations. The resulting magnetic field
displays propagating wave-like behavior. This behavior can be modelled in terms
of an \alpha\Omega dynamo. In most cases super-equipartition fields are
generated. By varying the fraction of helicity of the turbulence the
regeneration of poloidal fields via the helicity effect (corresponding to the
\alpha-effect) is regulated. The saturation level of the magnetic field in the
numerical models is consistent with a linear dependence on the ratio of the
fractional helicities of the small and large-scale fields, as predicted by a
simple nonlinear mean-field model. As the magnetic Reynolds number (Rm) based
on the wavenumber of the energy-carrying eddies is increased from 1 to 180, the
cycle frequency of the large-scale field is found to decrease by a factor of
about 6 in cases where the turbulence is fully helical. This is interpreted in
terms of the turbulent magnetic diffusivity, which is found to be only weakly
dependent on Rm.
