  In this article, we present direct numerical simulation results for the
expansion of spherical cap bubbles attached to a rigid wall due to a sudden
drop in the ambient pressure. The critical pressure drop beyond which the
bubble growth becomes unstable is found to match well with the predictions from
classical theory of heterogeneous nucleation imposing a quasi-static bubble
evolution. When the pressure drop is significantly higher than the critical
value, a liquid microlayer appears between the bubble and the wall. In this
regime, the interface outside the microlayer grows at an asymptotic velocity
that can be predicted from the Rayleigh--Plesset equation, while the contact
line evolves with another asymptotic velocity that scales with a
visco-capillary velocity that obeys the Cox--Voinov law. In general, three
distinctive regions can be distinguished: the region very close to the contact
line where dynamics is governed by visco-capillary effects, an intermediate
region controlled by inertio-viscous effects away from the contact line yet
inside the viscous boundary layer, and the region outside the boundary layer
dominated by inertial effects. The microlayer forms in a regime where the
capillary effects are confined in a region much smaller than the viscous
boundary layer thickness. In this regime, the global capillary number takes
values much larger then the critical capillary number for bubble nucleation,
and the microlayer height is controlled by viscous effects and not surface
tension.
