  Micro-bubbles are of significant interest due to the long-living signature
they leave behind naval ships. In order to numerically model and predict these
bubbles in naval applications, subgrid-scale models are required because of the
extreme separation of length- and time-scales between the macroscopic
geometries and the physical processes leading to the formation of these
bubbles. Yet, there is much that is unknown about the mechanism behind the
entrainment of such bubbles. Furthermore, quantitative information regarding
their size distribution and dependence on flow parameters is very limited.
Impact events are hypothesized to be the main contributor to the generation of
micro-bubbles. This is due to a phenomenon known as Mesler entrainment, which
has been observed in the context of the drop-pool impact problem. Namely, when
a water droplet with diameter of $\mathcal{O}(1mm)$ impacts a deep water pool
with an impact velocity of $\mathcal{O}(1m/s)$, hundreds of air micro-bubbles
are entrained into the pool. These bubbles have been found to be remnants of a
very thin air film entrapped between the two liquid bodies. These films have
extremely high aspect ratios and after being punctured, shed micro-bubbles
while retracting on time scales much shorter than the outer flow time scales.
This separation of time-scales, along with a lacking of studies on retracting
thin gas films has motivated us to study this fundamental problem with
numerical simulations in two and three dimensions. Using a diffuse interface
method, we perform two-phase simulations of retracting thin gas films in
initially static liquid backgrounds to gain understanding regarding this
problem and gather statistics that can be potentially used in a subgrid-scale
model to predict micro-bubble shedding from a thin gas film. Coupling a model
like this to a model that predicts the thin film characteristics ...
