  We study droplet-impact problems in a three-dimensional cylindrical or
equivalent two-dimensional Cartesian geometry. Such structures do have an
approximate experimental realization, and they are often simulated a test-bed
for computational methods. We focus on droplet impact on a smooth homogeneous
surface as well as head-on collision of two droplets. We perform an
energy-budget analysis and introduce a correlation which predicts the maximum
spreading radius as a function of Reynolds number and Weber number. We show how
the dissipation term in this analysis can be decomposed into boundary-layer
dissipation in the droplet lamella (where applicable), and head loss. We use
existing results in the literature (simulations and experiments), as well as
our own simulation results to validate the correlation. Dissipation by head
loss is a key term in the analysis: only by modeling it accurately can one
obtain good agreement between the simulations and the theory.
