  Studies of liquid jet impacts onto a deep liquid pool are of great
significance for a multitude of engineering and environmental applications.
During jet impact, the free surface of the pool deforms and a cavity is
generated. Simultaneously, the free surface of the cavity extends radially
outward and forms a rim. Eventually the cavity collapses by means of gas
inertia and surface tension. In this work we study numerically such cavity
collapse, under different impact velocities and ambient gas density conditions.
An axisymmetric numerical model, based on the volume of fluid method is
constructed in Basilisk C. This model is validated by qualitative and
quantitative comparison with theory and experiments, in a parameter range that
has not been previously explored. Our results show two distinct regimes in the
cavity collapse mechanism. By considering forces pulling along the interface,
we derive scaling arguments for the time of closure and maximum radius of the
cavity, based on the Weber number. For jets with uniform constant velocity from
tip to tail and $We \leq 150$ the cavity closure is capillary dominated and
happens below the surface (deep seal). In contrast, for $We \geq 200$ the
cavity closure happens above the surface (surface seal) and is dominated by the
gas entrainment and the pressure gradient that it causes. Our results provide
information for understanding pollutant transport during droplet impacts on
large bodies of water, and other engineering application, like additive
manufacturing, lithography and needle-free injections.
