  Numerical solutions of high-speed microdroplet impact onto a smooth solid
surface are computed, using the interFoam VoF solver of the OpenFOAM CFD
package. Toward the solid surface, the liquid microdroplet is moving with an
impinging gas flow, simulating the situation of ink droplets being deposited
onto substrate with a collimated mist jet in the Optomec Aerosol Jet printing
process. The computed values of maximum spread factor, for the range of
parameters of practical interest to Aerosol Jet printing, were found in very
good agreement with some of the correlation formulas proposed by previous
authors in the literature. Combining formulas selected from different authors
with appropriate modifications yields a maximum spread factor formula that can
be used for first-order evaluations of deposited in droplet size during the
Aerosol Jet technology development. The computational results also illustrate
droplet impact dynamics with lamella shape evolution throughout the spreading,
receding-relaxation, and wetting equilibrium phases, consistent with that
observed and described by many previous authors. This suggests a
scale-invariant nature of the basic droplet impact behavior such that
experiments with larger droplets at the same nondimensional parameter values
may be considered for studying microdroplet impact dynamics. Significant free
surface oscillations can be observed when the droplet viscosity is relatively
low. The border line between periodic free surface oscillations and aperiodic
creeping to capillary equilibrium free surface shape appears at the value of
Ohnesorge number around 0.25. Droplet bouncing after receding is prompted with
large contact angles at solid surface (as consistent with findings reported in
the literature), but can be suppressed by increasing the droplet viscosity.
