  We present nonlinear mean-field alpha-Omega dynamo simulations in spherical
geometry with simplified profiles of kinematic alpha effect and shear. We take
magnetic helicity evolution into account by solving a dynamical equation for
the magnetic alpha effect. This gives a consistent description of the quenching
mechanism in mean-field dynamo models. The main goal of this work is to explore
the effects of this quenching mechanism in solar-like geometry, and in
particular to investigate the role of magnetic helicity fluxes, specifically
diffusive and Vishniac-Cho (VC) fluxes, at large magnetic Reynolds numbers
(Rm). For models with negative radial shear or positive latitudinal shear, the
magnetic alpha effect has predominantly negative (positive) sign in the
northern (southern) hemisphere. In the absence of fluxes, we find that the
magnetic energy follows an Rm^-1 dependence, as found in previous works. This
catastrophic quenching is alleviated in models with diffusive magnetic helicity
fluxes resulting in magnetic fields comparable to the equipartition value even
for Rm=10^7. On the other hand, models with a shear-driven Vishniac-Cho flux
show an increase of the amplitude of the magnetic field with respect to models
without fluxes, but only for Rm<10^4. This is mainly a consequence of assuming
a vacuum outside the Sun which cannot support a significant VC flux across the
boundary. However, in contrast with the diffusive flux, the VC flux modifies
the distribution of the magnetic field. In addition, if an ill-determined
scaling factor in the expression for the VC flux is large enough, subcritical
dynamo action is possible that is driven by the action of shear and the
divergence of current helicity flux.
