When a bubble collapses mildly the interior pressure field is spatially uniform; this is
an assumption often made to close the Rayleigh–Plesset equation of bubble dynamics.
The present work is a study of the self-consistency of this assumption, particularly
in the case of violent collapses. To begin, an approximation is developed for a
spatially non-uniform pressure field, which in a violent collapse is inertially driven.
Comparisons of this approximation show good agreement with direct numerical
solutions of the compressible Navier–Stokes equations with heat and mass transfer.
With knowledge of the departures from pressure uniformity in strongly forced bubbles,
one is in a position to develop criteria to assess when pressure uniformity is a
physically valid assumption, as well as the significance of wave motion in the gas.
An examination of the Rayleigh–Plesset equation reveals that its solutions are quite
accurate even in the case of significant inertially driven spatial inhomogeneity in the
pressure field, and even when wave-like motions in the gas are present. This extends
the range of utility of the Rayleigh–Plesset equation well into the regime where the
Mach number is no longer small; at the same time the theory sheds light on the
interior of a strongly forced bubble.